Re: [postgis-devel] Geog/Geom Hack
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Re: [postgis-devel] Geog/Geom Hack
by Paragon Corporation-2
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Paul,
For what its worth, here is another reason why I don't like this idea and I think we should at least think about its ramifications more so should put it off for consideration until 2.0. In geometry processing, its common practice to apply a lot of functions in succession process1(process2(process3(geometry/geography) With your hackish approach -- the unsuspecting novice user will be incurring a lot of transformation rounding errors with each process The advanced user, won't know if this is okay or not -- because they can't tell by looking at the function call the hidden transformations going on. If these did not exist, they would transform once before the processes and once after) and incurr much less penalty But if they both exist, they will treat them as being on equal footing ST_Buffer(geometry) and ST_Buffer(geography) So your approach while well-meaning gives a questionable benefit to novices and is putting experienced users at a disadvantage. Thanks, Regina -----Original Message----- From: postgis-devel-bounces@... [mailto:postgis-devel-bounces@...] On Behalf Of Paragon Corporation Sent: Friday, October 30, 2009 11:54 PM To: 'PostGIS Development Discussion' Cc: 'PostGIS Users Discussion' Subject: Re: [postgis-devel] Geog/Geom Hack Paul, I suppose we can't just put this decision off till 2.0. Isn't this a bit of scope creep? I'm not absolutely sure which way is better, but I know the cost of rolling back the change is more. If you are going to do this, how many functions are you planning to do this for? I'm cc'ing the postgis users group too to get more of an opinion on this topic. So the question is it it a good idea to introduce a hack that transforms a geography into what we call BestSRID to perform geometry operations on and then transform back. My concern is that this is a silent operation that gives the impression that these functions are natively done in spheroid space just for the benefit of catering to less technical users. http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.c#L541 So you can't really tell by looking the penalty Main examples of this as shown for ST_Buffer CREATE OR REPLACE FUNCTION _ST_BestSRID(geography, geography) 530 RETURNS integer 531 AS 'MODULE_PATHNAME','geography_bestsrid' 532 LANGUAGE 'C' IMMUTABLE STRICT; 533 534 -- Availability: 1.5.0 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) 536 RETURNS integer 537 AS 'SELECT _ST_BestSRID($1,$1)' 538 LANGUAGE 'SQL' IMMUTABLE STRICT; 539 540 -- Availability: 1.5.0 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) 542 RETURNS geography 543 AS 'SELECT geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), _ST_BestSRID($1)), $2), 4326))' 544 LANGUAGE 'SQL' IMMUTABLE STRICT; 545 Thanks, Regina -----Original Message----- From: postgis-devel-bounces@... [mailto:postgis-devel-bounces@...] On Behalf Of Paul Ramsey Sent: Friday, October 30, 2009 11:07 PM To: PostGIS Development Discussion Subject: Re: [postgis-devel] Geog/Geom Hack We're going to have to agree to disagree on this one, Regina. Catering to the less technical users is what this exercise is all about, to my mind, and that includes allowing easy flipping into geometry for calculations that aren't supported in geography yet. Oracle does this too. What do other folks think? P. On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation <lr@...> wrote: > Paul, > Hmm when I am comparing distance of two geometries in different > spatial refs which I do a lot. > > I still don't like the hack even if you disregard the above or if you > must hack -- don't give it the same name as the non-hacked functions. > > the whole idea of picking BestSRID for a person to cater to less > technical users I find extremely annoying as I can think of 20 > "BestSRID" depending on what I am doing. If they get to that level of > sophistication, I would rather have them think a little more and > understand the implications of those decisions. > > We must learn to crawl before we can learn to walk,because walking > without understanding will just get you into trouble in the long run. > > > Thanks, > Regina > > -----Original Message----- > From: postgis-devel-bounces@... > [mailto:postgis-devel-bounces@...] On Behalf Of > Paul Ramsey > Sent: Friday, October 30, 2009 9:47 PM > To: PostGIS Development Discussion > Subject: Re: [postgis-devel] Geog/Geom Hack > > You *can*, but I strongly doubt you *will*. Because there's nothing in > geography that isn't already in geometry. So you as a primary geometry > user are going to have no working need to cast things to geography. > > On the other hand, the very first question from users of geography > will be "how can I access <geometry function N>?" So having a > relatively full set of functions already available in geography makes > sense to me, even if they are hacked in with a planar trick. > > P. > > On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation <lr@...> wrote: >> Paul, >> I can put a functional geography index on can't I and take advantage >> of geography index bindings? >> >> Lets say I have a large network of tables broken out by region so I >> know a specific table has one srid. >> >> For many queries, I may go to that table directly or if I'm doing >> single geometry processing, really don't care what srid as long as >> its in utm or whatever - so I can use the full power of GEOS. >> >> For my across the board distance checks and so forth, I would want to >> use geography and I could use a geography index if I put a functional >> geography index on my geometry correct? Though that needs some more > testing. >> >> >> So in short if 90% of my workload involves geometry processing, I >> will want to keep my data in geometry >> >> But the 10% I would want to convert to geography on the fly. >> >> Thanks, >> Regina >> >> -----Original Message----- >> From: postgis-devel-bounces@... >> [mailto:postgis-devel-bounces@...] On Behalf Of >> Paul Ramsey >> Sent: Friday, October 30, 2009 8:34 PM >> To: PostGIS Development Discussion >> Subject: Re: [postgis-devel] Geog/Geom Hack >> >> I'm not sure I understand why you would ever convert a geometry to a >> geography as part of a query on a geometry table. I fully expect >> geography to be used as a storage type, because of the utility of >> having the correct spherical indexes, which are not available when >> you're just converting in via a cast. Since there's no functions >> available on geography that are not already available on geometry, >> why would you ever do a geometry->geography cast unless you are (a) >> testing geography or (b) bulk converting a table into geography for > storage in that type. >> >> P. >> >> >> >> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation <lr@...> wrote: >>> Paul, >>> I would rather you didn't for 2 reasons >>> >>> 1) I'm lazy and for each of these things we'd have to apply the text >>> additional function proto hack to prevent from it breaking geometry. >>> which we will probably end up taking out anyway. >>> >>> 2) I don't like the hiddenness of it since it becomes especially >>> annoying if you have your native in geometry and you are converting >>> to geography for a special usecase, then you end up with a slower >>> implementation >>> >>> as you would really end up doing accidentally >>> >>> geometry -> geography -> geometry ->operation (and why do I want my >>> calcs done in UTM?) >>> >>> Instead of the more efficient >>> >>> geometry -> operation >>> >>> Thanks, >>> Regina >>> >>> -----Original Message----- >>> From: postgis-devel-bounces@... >>> [mailto:postgis-devel-bounces@...] On Behalf Of >>> Paul Ramsey >>> Sent: Friday, October 30, 2009 8:16 PM >>> To: PostGIS Development Discussion >>> Subject: [postgis-devel] Geog/Geom Hack >>> >>> I'm interested to know what the general opinion is of the trick I've >>> used on >>> ST_Buffer(geography): >>> >>> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in. >>> c >>> #L541 >>> >>> I ask because I could apply the same idea to the larger suite of OGC >>> SFSQL predicates before release. Is half-a-loaf better than no loaf >>> in >> this case? >>> (Note that there will be failure cases for really large geometry, >>> like a polygon of "Asia" or "Russia" that have polygons over the >>> dateline.) >>> >>> P. >>> _______________________________________________ >>> postgis-devel mailing list >>> postgis-devel@... >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>> >>> >>> >>> _______________________________________________ >>> postgis-devel mailing list >>> postgis-devel@... >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>> >> _______________________________________________ >> postgis-devel mailing list >> postgis-devel@... >> http://postgis.refractions.net/mailman/listinfo/postgis-devel >> >> >> >> _______________________________________________ >> postgis-devel mailing list >> postgis-devel@... >> http://postgis.refractions.net/mailman/listinfo/postgis-devel >> > _______________________________________________ > postgis-devel mailing list > postgis-devel@... > http://postgis.refractions.net/mailman/listinfo/postgis-devel > > > _______________________________________________ > postgis-devel mailing list > postgis-devel@... > http://postgis.refractions.net/mailman/listinfo/postgis-devel > postgis-devel mailing list postgis-devel@... http://postgis.refractions.net/mailman/listinfo/postgis-devel _______________________________________________ postgis-devel mailing list postgis-devel@... http://postgis.refractions.net/mailman/listinfo/postgis-devel _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: [postgis-devel] Geog/Geom Hack
by Stephen Woodbridge
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Hi All,
For whatever its worth: 1) I really like the fact that we are addressing usability for the masses. Just making it do the intuitive thing is good. 2) As someone that has invested a lot of time to learn the ins and outs, I'm not sure I like the fact that all my functions may start behaving differently as this thread seems to be implying. I like having control over how my queries are evaluated and optimized. 3) Without knowing all the nuances of this thread, I would be in favor of Nicklas' suggestion of add new function names for the hacks. Before reading his response, I was thinking we could name all these functions STT_... again the extra T for transform. Its all goodness in my book, and I appreciate all the work everyone is doing on this and look forward to a future release where I can try it out. Best regards, -Steve W Paragon Corporation wrote: > > Nicklas and Paul, > > Yap that's the main point. To add > > I'm not really in disagreement with Paul. I see his point too. I'm > just prodding him to think about all his use cases a little more because > I don't feel he has. > > My feelings to sum up > 1) We have not thought about the complete ramifications of this hack and > I'm really concerned about the novice that transitions to an expert > rather than just getting them hooked on PostGIS. Perhaps I'm being > overly silly with that and even said, Paul's approach might be an easier > to transition solution. > > 2) My concern is the penalty of putting it in and having to take it out > later might be very great (both from a code, testing, as well as a > mindset perspective). I just feel it needs more thought and testing and > really if we want to make our December deadline, I don't want it rushed > in so lightly. > > Unless of course Paul -- you want to wait till January or February to > release 1.5? > > Now the ST_Max_Distance is a separate issue. I would put in the > ST_ConvexHull hack in place. The reason being is that it just improves > performance any way I can think you slice it and an experienced user > would do exactly the same thing always and when you finally incorporate > it into the core function, there is no change in existing code just a > speed improvement. So to me its basically our ST_DWithin hack -- a very > tried and trued obvious answer. Its an implementation detail with no > clear leaky effects. > > With that said, there are some clear functions in geometry that are safe > to put a geography cover over. Those ones where there is clearly only > one answer and don't involve transformation. > > like ST_X, ST_Y etc. That don't require transformation so no screw up > in data. Also observe that even the geometry(geography .... in these > there is no penalty becuase the geometry/geography isn't changing so the > planner can cache the geometry to geography conversion. The > ST_Transformation ones however, the geometry/geography is changing > slightly at each step since ST_Tranformation is a lossy operation so you > are not only incurring overhead (because these answers can't be cached), > but also adding in extra errors . > > To me this is a bleeding abstraction and that is the main reason I don't > like it. > > So getting back to you Paul, > > What functions exactly are you planning to put a veil over? ST_Buffer > well that one is used so much and is not as exact anyway that I suppose > I can grudgingly accept that as okay. > > Thanks, > Regina > > > *From:* postgis-devel-bounces@... > [mailto:postgis-devel-bounces@...] *On Behalf Of > *nicklas.aven@... > *Sent:* Saturday, October 31, 2009 10:04 AM > *To:* PostGIS Development Discussion > *Subject:* Re: [postgis-devel] Geog/Geom Hack > > Hallo > > I can see the points from both of you. I think the most important > argument from you Regina is that it is not transparent enough. A > skillfull user trying postgis might be disapointed when realizing that > the nested functions caused an unnecessary big rounding-error. > But if it is obvious that it is a "special" function at least for the > experienced user knowing about common function-names I don't think it is > a big problem and might work as an easy shortcut at least during the > process of learning. > > As I understand it this could be a solution for using many functions > against geography so, why not note it in the function name like: > ST_tBuffer for transformed buffer. Then when time is to introduse a > "real" variant of the function they can coexist and it will not change > the bahavior inside an application without someone consciously changes > the function name and remove the t. > > the t would be independent of geography-geometry in semantics and just > indicate that it is a lower-precision variant. I fit was commonly used > it would work as a warning to experienced users. > > I have a similar question about st_max_distance. The function gets very > much more effective when ran together with convexhull. I saw the trick > in ST_MinimumBoundingCircle and id makes a big difference to do : > st_max_distance(st_convexhull(the_geom)) instead of just > st_max_distance(the_geom). > The question is: Should that be put in the sql-function? > My opinion now is that we just tell about it in the documentation and > aims at doing that trick internally in C in the future. Maybe together > with moving the whole convexhull to postgis-native from geos. It didn't > look that impossible fromthe JTS-code. > > /Nicklas > > > 2009-10-31 Paul Ramsey wrote: > > I still think I'm right :) Honestly, I've got to a lot of trouble to > >make this stuff for newbies, and I don't think "learn how it works" is > >the right answer for them. They had that option before, but taking GIS > >101 is not an option for these people, they need something that "just > >works". It's easier to teach the experienced people the pitfalls than > >the inexperienced people the basics. > > > >BTW, I just upgraded distance_sphere and distance_spheroid to be as > >powerful (handling point/line/polygon) as the geography variants, > >removing excuses for transforming geometries into geographies for > >processing purposes. > > > >P. > > > >On Fri, Oct 30, 2009 at 9:15 PM, Paragon Corporation wrote: > >> Paul, > >> For what its worth, here is another reason why I don't like this > idea and I > >> think we should at least think about its ramifications more so > should put it > >> off for consideration until 2.0. > >> > >> In geometry processing, its common practice to apply a lot of > functions in > >> succession > >> > >> process1(process2(process3(geometry/geography) > >> > >> With your hackish approach -- the unsuspecting novice user will be > incurring > >> a lot of transformation rounding errors with each process > >> > >> The advanced user, won't know if this is okay or not -- because they > can't > >> tell by looking at the function call the hidden transformations > going on. > >> > >> If these did not exist, they would transform once before the > processes and > >> once after) and incurr much less penalty > >> > >> But if they both exist, they will treat them as being on equal footing > >> > >> ST_Buffer(geometry) and ST_Buffer(geography) > >> > >> > >> So your approach while well-meaning gives a questionable benefit to > novices > >> and is putting experienced users at a disadvantage. > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf Of > Paragon > >> Corporation > >> Sent: Friday, October 30, 2009 11:54 PM > >> To: 'PostGIS Development Discussion' > >> Cc: 'PostGIS Users Discussion' > >> Subject: Re: [postgis-devel] Geog/Geom Hack > >> > >> Paul, > >> I suppose we can't just put this decision off till 2.0. Isn't this > a bit of > >> scope creep? I'm not absolutely sure which way is better, but I > know the > >> cost of rolling back the change is more. > >> > >> If you are going to do this, how many functions are you planning to > do this > >> for? > >> > >> I'm cc'ing the postgis users group too to get more of an opinion on this > >> topic. > >> > >> So the question is it it a good idea to introduce a hack that > transforms a > >> geography into what we call BestSRID to perform geometry operations > on and > >> then transform back. My concern is that this is a silent operation that > >> gives the impression that these functions are natively done in spheroid > >> space just for the benefit of catering to less technical users. > >> > >> > http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.c#L541 > >> > >> So you can't really tell by looking the penalty > >> > >> Main examples of this as shown for ST_Buffer > >> > >> CREATE OR REPLACE FUNCTION _ST_BestSRID(geography, geography) > >> 530 RETURNS integer > >> 531 AS 'MODULE_PATHNAME','geography_bestsrid' > >> 532 LANGUAGE 'C' IMMUTABLE STRICT; > >> 533 > >> 534 -- Availability: 1.5.0 > >> 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) > >> 536 RETURNS integer > >> 537 AS 'SELECT _ST_BestSRID($1,$1)' > >> 538 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 539 > >> 540 -- Availability: 1.5.0 > >> 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) > >> 542 RETURNS geography > >> 543 AS 'SELECT > >> geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), > >> _ST_BestSRID($1)), $2), 4326))' > >> 544 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 545 > >> > >> > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf Of Paul > >> Ramsey > >> Sent: Friday, October 30, 2009 11:07 PM > >> To: PostGIS Development Discussion > >> Subject: Re: [postgis-devel] Geog/Geom Hack > >> > >> We're going to have to agree to disagree on this one, Regina. > Catering to > >> the less technical users is what this exercise is all about, to my > mind, and > >> that includes allowing easy flipping into geometry for calculations that > >> aren't supported in geography yet. Oracle does this too. > >> > >> What do other folks think? > >> > >> P. > >> > >> On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation wrote: > >>> Paul, > >>> Hmm when I am comparing distance of two geometries in different > >>> spatial refs which I do a lot. > >>> > >>> I still don't like the hack even if you disregard the above or if you > >>> must hack -- don't give it the same name as the non-hacked functions. > >>> > >>> the whole idea of picking BestSRID for a person to cater to less > >>> technical users I find extremely annoying as I can think of 20 > >>> "BestSRID" depending on what I am doing. If they get to that level of > >>> sophistication, I would rather have them think a little more and > >>> understand the implications of those decisions. > >>> > >>> We must learn to crawl before we can learn to walk,because walking > >>> without understanding will just get you into trouble in the long run. > >>> > >>> > >>> Thanks, > >>> Regina > >>> > >>> -----Original Message----- > >>> From: postgis-devel-bounces@... > >>> [mailto:postgis-devel-bounces@...] On Behalf Of > >>> Paul Ramsey > >>> Sent: Friday, October 30, 2009 9:47 PM > >>> To: PostGIS Development Discussion > >>> Subject: Re: [postgis-devel] Geog/Geom Hack > >>> > >>> You *can*, but I strongly doubt you *will*. Because there's nothing in > >>> geography that isn't already in geometry. So you as a primary geometry > >>> user are going to have no working need to cast things to geography. > >>> > >>> On the other hand, the very first question from users of geography > >>> will be "how can I access ?" So having a > >>> relatively full set of functions already available in geography makes > >>> sense to me, even if they are hacked in with a planar trick. > >>> > >>> P. > >>> > >>> On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation wrote: > >>>> Paul, > >>>> I can put a functional geography index on can't I and take advantage > >>>> of geography index bindings? > >>>> > >>>> Lets say I have a large network of tables broken out by region so I > >>>> know a specific table has one srid. > >>>> > >>>> For many queries, I may go to that table directly or if I'm doing > >>>> single geometry processing, really don't care what srid as long as > >>>> its in utm or whatever - so I can use the full power of GEOS. > >>>> > >>>> For my across the board distance checks and so forth, I would want to > >>>> use geography and I could use a geography index if I put a functional > >>>> geography index on my geometry correct? Though that needs some more > >>> testing. > >>>> > >>>> > >>>> So in short if 90% of my workload involves geometry processing, I > >>>> will want to keep my data in geometry > >>>> > >>>> But the 10% I would want to convert to geography on the fly. > >>>> > >>>> Thanks, > >>>> Regina > >>>> > >>>> -----Original Message----- > >>>> From: postgis-devel-bounces@... > >>>> [mailto:postgis-devel-bounces@...] On Behalf Of > >>>> Paul Ramsey > >>>> Sent: Friday, October 30, 2009 8:34 PM > >>>> To: PostGIS Development Discussion > >>>> Subject: Re: [postgis-devel] Geog/Geom Hack > >>>> > >>>> I'm not sure I understand why you would ever convert a geometry to a > >>>> geography as part of a query on a geometry table. I fully expect > >>>> geography to be used as a storage type, because of the utility of > >>>> having the correct spherical indexes, which are not available when > >>>> you're just converting in via a cast. Since there's no functions > >>>> available on geography that are not already available on geometry, > >>>> why would you ever do a geometry->geography cast unless you are (a) > >>>> testing geography or (b) bulk converting a table into geography for > >>> storage in that type. > >>>> > >>>> P. > >>>> > >>>> > >>>> > >>>> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation wrote: > >>>>> Paul, > >>>>> I would rather you didn't for 2 reasons > >>>>> > >>>>> 1) I'm lazy and for each of these things we'd have to apply the text > >>>>> additional function proto hack to prevent from it breaking geometry. > >>>>> which we will probably end up taking out anyway. > >>>>> > >>>>> 2) I don't like the hiddenness of it since it becomes especially > >>>>> annoying if you have your native in geometry and you are converting > >>>>> to geography for a special usecase, then you end up with a slower > >>>>> implementation > >>>>> > >>>>> as you would really end up doing accidentally > >>>>> > >>>>> geometry -> geography -> geometry ->operation (and why do I want my > >>>>> calcs done in UTM?) > >>>>> > >>>>> Instead of the more efficient > >>>>> > >>>>> geometry -> operation > >>>>> > >>>>> Thanks, > >>>>> Regina > >>>>> > >>>>> -----Original Message----- > >>>>> From: postgis-devel-bounces@... > >>>>> [mailto:postgis-devel-bounces@...] On Behalf Of > >>>>> Paul Ramsey > >>>>> Sent: Friday, October 30, 2009 8:16 PM > >>>>> To: PostGIS Development Discussion > >>>>> Subject: [postgis-devel] Geog/Geom Hack > >>>>> > >>>>> I'm interested to know what the general opinion is of the trick I've > >>>>> used on > >>>>> ST_Buffer(geography): > >>>>> > >>>>> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in. > >>>>> c > >>>>> #L541 > >>>>> > >>>>> I ask because I could apply the same idea to the larger suite of OGC > >>>>> SFSQL predicates before release. Is half-a-loaf better than no loaf > >>>>> in > >>>> this case? > >>>>> (Note that there will be failure cases for really large geometry, > >>>>> like a polygon of "Asia" or "Russia" that have polygons over the > >>>>> dateline.) > >>>>> > >>>>> P. > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>>> > >>>>> > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >_______________________________________________ > >postgis-devel mailing list > >postgis-devel@... > >http://postgis.refractions.net/mailman/listinfo/postgis-devel > > > > > > > ------------------------------------------------------------------------ > > _______________________________________________ > postgis-users mailing list > postgis-users@... > http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: [postgis-devel] Geog/Geom Hack
by Paragon Corporation-2
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Steve,
My sentiments exactly. The only issue I can see with introducing STT is that it does add potentially a lot of functions we would need to possibly deprecate or remove in future versions. Its almost better to just throw these out there as contrib functions and let people pick the ones they need. Here is yet another example of why I think Paul's hack is a bleeding abstraction Lets suppose you have a huge mass like a continent that no current spatial ref effectively covers What exactly does the magical BestSRID function return? In a true ST_buffer for geography its a non-issue, but since this is a hack, the answer is clearly wrong and advanced users would approach it differently perhaps by dicing it,buffer each add union the individual back to geography. Of course I suppose you could say -- well It's clearly wrong now (for that 1% case), but we can fix it easily under the covers later without people having to change their code -- which I can only guess is what Paul is thinking thus my complaints of the effort to take it out he sees as a non-issue. To me its covering a baby horse in a big horse costume and passing it off as a grown up. You'll start showing it horse porn and it will start doing ridiculous things with it :) Then there is the agg ST_Union (how would you do that?) when you can span so many BEST SRIDs. Thanks, Regina -----Original Message----- From: postgis-users-bounces@... [mailto:postgis-users-bounces@...] On Behalf Of Stephen Woodbridge Sent: Saturday, October 31, 2009 12:47 PM To: PostGIS Users Discussion Cc: 'PostGIS Development Discussion' Subject: Re: [postgis-users] [postgis-devel] Geog/Geom Hack Hi All, For whatever its worth: 1) I really like the fact that we are addressing usability for the masses. Just making it do the intuitive thing is good. 2) As someone that has invested a lot of time to learn the ins and outs, I'm not sure I like the fact that all my functions may start behaving differently as this thread seems to be implying. I like having control over how my queries are evaluated and optimized. 3) Without knowing all the nuances of this thread, I would be in favor of Nicklas' suggestion of add new function names for the hacks. Before reading his response, I was thinking we could name all these functions STT_... again the extra T for transform. Its all goodness in my book, and I appreciate all the work everyone is doing on this and look forward to a future release where I can try it out. Best regards, -Steve W Paragon Corporation wrote: > > Nicklas and Paul, > > Yap that's the main point. To add > > I'm not really in disagreement with Paul. I see his point too. I'm > just prodding him to think about all his use cases a little more > because I don't feel he has. > > My feelings to sum up > 1) We have not thought about the complete ramifications of this hack > and I'm really concerned about the novice that transitions to an > expert rather than just getting them hooked on PostGIS. Perhaps I'm > being overly silly with that and even said, Paul's approach might be > an easier to transition solution. > > 2) My concern is the penalty of putting it in and having to take it > out later might be very great (both from a code, testing, as well as > a mindset perspective). I just feel it needs more thought and testing > and really if we want to make our December deadline, I don't want it > rushed in so lightly. > > Unless of course Paul -- you want to wait till January or February to > release 1.5? > > Now the ST_Max_Distance is a separate issue. I would put in the > ST_ConvexHull hack in place. The reason being is that it just > improves performance any way I can think you slice it and an > experienced user would do exactly the same thing always and when you > finally incorporate it into the core function, there is no change in > existing code just a speed improvement. So to me its basically our > ST_DWithin hack -- a very tried and trued obvious answer. Its an > implementation detail with no clear leaky effects. > > With that said, there are some clear functions in geometry that are > safe to put a geography cover over. Those ones where there is clearly > only one answer and don't involve transformation. > > like ST_X, ST_Y etc. That don't require transformation so no screw up > in data. Also observe that even the geometry(geography .... in these > there is no penalty becuase the geometry/geography isn't changing so > the planner can cache the geometry to geography conversion. The > ST_Transformation ones however, the geometry/geography is changing > slightly at each step since ST_Tranformation is a lossy operation so > you are not only incurring overhead (because these answers can't be > cached), but also adding in extra errors . > > To me this is a bleeding abstraction and that is the main reason I > don't like it. > > So getting back to you Paul, > > What functions exactly are you planning to put a veil over? ST_Buffer > well that one is used so much and is not as exact anyway that I > suppose I can grudgingly accept that as okay. > > Thanks, > Regina > > > *From:* postgis-devel-bounces@... > [mailto:postgis-devel-bounces@...] *On Behalf Of > *nicklas.aven@... > *Sent:* Saturday, October 31, 2009 10:04 AM > *To:* PostGIS Development Discussion > *Subject:* Re: [postgis-devel] Geog/Geom Hack > > Hallo > > I can see the points from both of you. I think the most important > argument from you Regina is that it is not transparent enough. A > skillfull user trying postgis might be disapointed when realizing that > the nested functions caused an unnecessary big rounding-error. > But if it is obvious that it is a "special" function at least for the > experienced user knowing about common function-names I don't think it > is a big problem and might work as an easy shortcut at least during > the process of learning. > > As I understand it this could be a solution for using many functions > against geography so, why not note it in the function name like: > ST_tBuffer for transformed buffer. Then when time is to introduse a > "real" variant of the function they can coexist and it will not change > the bahavior inside an application without someone consciously changes > the function name and remove the t. > > the t would be independent of geography-geometry in semantics and just > indicate that it is a lower-precision variant. I fit was commonly used > it would work as a warning to experienced users. > > I have a similar question about st_max_distance. The function gets > very much more effective when ran together with convexhull. I saw the > trick in ST_MinimumBoundingCircle and id makes a big difference to do : > st_max_distance(st_convexhull(the_geom)) instead of just > st_max_distance(the_geom). > The question is: Should that be put in the sql-function? > My opinion now is that we just tell about it in the documentation and > aims at doing that trick internally in C in the future. Maybe together > with moving the whole convexhull to postgis-native from geos. It > didn't look that impossible fromthe JTS-code. > > /Nicklas > > > 2009-10-31 Paul Ramsey wrote: > > I still think I'm right :) Honestly, I've got to a lot of trouble to > >make this stuff for newbies, and I don't think "learn how it works" > is >the right answer for them. They had that option before, but > taking GIS > >101 is not an option for these people, they need something that > "just >works". It's easier to teach the experienced people the > pitfalls than >the inexperienced people the basics. > > > >BTW, I just upgraded distance_sphere and distance_spheroid to be as > >powerful (handling point/line/polygon) as the geography variants, > >removing excuses for transforming geometries into geographies for > >processing purposes. > > > >P. > > > >On Fri, Oct 30, 2009 at 9:15 PM, Paragon Corporation wrote: > >> Paul, > >> For what its worth, here is another reason why I don't like this > idea and I >> think we should at least think about its ramifications > more so should put it >> off for consideration until 2.0. > >> > >> In geometry processing, its common practice to apply a lot of > functions in >> succession >> >> > process1(process2(process3(geometry/geography) > >> > >> With your hackish approach -- the unsuspecting novice user will be > incurring >> a lot of transformation rounding errors with each > process >> >> The advanced user, won't know if this is okay or not > -- because they can't >> tell by looking at the function call the > hidden transformations going on. > >> > >> If these did not exist, they would transform once before the > processes and >> once after) and incurr much less penalty >> >> But > if they both exist, they will treat them as being on equal footing >> > >> ST_Buffer(geometry) and ST_Buffer(geography) >> >> >> So your > approach while well-meaning gives a questionable benefit to novices > >> and is putting experienced users at a disadvantage. > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf > Of Paragon >> Corporation >> Sent: Friday, October 30, 2009 11:54 PM > >> To: 'PostGIS Development Discussion' > >> Cc: 'PostGIS Users Discussion' > >> Subject: Re: [postgis-devel] Geog/Geom Hack >> >> Paul, >> I > suppose we can't just put this decision off till 2.0. Isn't this a > bit of >> scope creep? I'm not absolutely sure which way is better, > but I know the >> cost of rolling back the change is more. > >> > >> If you are going to do this, how many functions are you planning > to do this >> for? > >> > >> I'm cc'ing the postgis users group too to get more of an opinion > on this >> topic. > >> > >> So the question is it it a good idea to introduce a hack that > transforms a >> geography into what we call BestSRID to perform > geometry operations on and >> then transform back. My concern is > that this is a silent operation that >> gives the impression that > these functions are natively done in spheroid >> space just for the > benefit of catering to less technical users. > >> > >> > http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.c > #L541 > >> > >> So you can't really tell by looking the penalty >> >> Main > examples of this as shown for ST_Buffer >> >> CREATE OR REPLACE > FUNCTION _ST_BestSRID(geography, geography) > >> 530 RETURNS integer > >> 531 AS 'MODULE_PATHNAME','geography_bestsrid' > >> 532 LANGUAGE 'C' IMMUTABLE STRICT; > >> 533 > >> 534 -- Availability: 1.5.0 > >> 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) > >> 536 RETURNS integer > >> 537 AS 'SELECT _ST_BestSRID($1,$1)' > >> 538 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 539 > >> 540 -- Availability: 1.5.0 > >> 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) > >> 542 RETURNS geography > >> 543 AS 'SELECT > >> geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), > >> _ST_BestSRID($1)), $2), 4326))' > >> 544 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 545 > >> > >> > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf > Of Paul >> Ramsey >> Sent: Friday, October 30, 2009 11:07 PM >> To: > PostGIS Development Discussion >> Subject: Re: [postgis-devel] > Geog/Geom Hack >> >> We're going to have to agree to disagree on > this one, Regina. > Catering to > >> the less technical users is what this exercise is all about, to my > mind, and >> that includes allowing easy flipping into geometry for > calculations that >> aren't supported in geography yet. Oracle does > this too. > >> > >> What do other folks think? > >> > >> P. > >> > >> On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation wrote: > >>> Paul, > >>> Hmm when I am comparing distance of two geometries in different > >>> spatial refs which I do a lot. > >>> > >>> I still don't like the hack even if you disregard the above or if > you >>> must hack -- don't give it the same name as the non-hacked > >>> > >>> the whole idea of picking BestSRID for a person to cater to less > >>> technical users I find extremely annoying as I can think of 20 > >>> "BestSRID" depending on what I am doing. If they get to that > level of >>> sophistication, I would rather have them think a little > more and >>> understand the implications of those decisions. > >>> > >>> We must learn to crawl before we can learn to walk,because > walking >>> without understanding will just get you into trouble in the long run. > >>> > >>> > >>> Thanks, > >>> Regina > >>> > >>> -----Original Message----- > >>> From: postgis-devel-bounces@... > >>> [mailto:postgis-devel-bounces@...] On Behalf > Of >>> Paul Ramsey >>> Sent: Friday, October 30, 2009 9:47 PM >>> > To: PostGIS Development Discussion >>> Subject: Re: [postgis-devel] > Geog/Geom Hack >>> >>> You *can*, but I strongly doubt you *will*. > Because there's nothing in >>> geography that isn't already in > geometry. So you as a primary geometry >>> user are going to have no > working need to cast things to geography. > >>> > >>> On the other hand, the very first question from users of > geography >>> will be "how can I access ?" So having a >>> > relatively full set of functions already available in geography makes > >>> sense to me, even if they are hacked in with a planar trick. > >>> > >>> P. > >>> > >>> On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation wrote: > >>>> Paul, > >>>> I can put a functional geography index on can't I and take > advantage >>>> of geography index bindings? > >>>> > >>>> Lets say I have a large network of tables broken out by region > so I >>>> know a specific table has one srid. > >>>> > >>>> For many queries, I may go to that table directly or if I'm > doing >>>> single geometry processing, really don't care what srid as > long as >>>> its in utm or whatever - so I can use the full power of > >>>> > >>>> For my across the board distance checks and so forth, I would > want to >>>> use geography and I could use a geography index if I put > a functional >>>> geography index on my geometry correct? Though > that needs some more >>> testing. > >>>> > >>>> > >>>> So in short if 90% of my workload involves geometry processing, > I >>>> will want to keep my data in geometry >>>> >>>> But the 10% > I would want to convert to geography on the fly. > >>>> > >>>> Thanks, > >>>> Regina > >>>> > >>>> -----Original Message----- > >>>> From: postgis-devel-bounces@... > >>>> [mailto:postgis-devel-bounces@...] On Behalf > Of >>>> Paul Ramsey >>>> Sent: Friday, October 30, 2009 8:34 PM > >>>> To: PostGIS Development Discussion >>>> Subject: Re: > [postgis-devel] Geog/Geom Hack >>>> >>>> I'm not sure I understand > why you would ever convert a geometry to a >>>> geography as part of > a query on a geometry table. I fully expect >>>> geography to be used > as a storage type, because of the utility of >>>> having the correct > spherical indexes, which are not available when >>>> you're just > converting in via a cast. Since there's no functions >>>> available > on geography that are not already available on geometry, >>>> why > would you ever do a geometry->geography cast unless you are (a) >>>> > testing geography or (b) bulk converting a table into geography for > >>> storage in that type. > >>>> > >>>> P. > >>>> > >>>> > >>>> > >>>> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation wrote: > >>>>> Paul, > >>>>> I would rather you didn't for 2 reasons >>>>> >>>>> 1) I'm > lazy and for each of these things we'd have to apply the text >>>>> > additional function proto hack to prevent from it breaking geometry. > >>>>> which we will probably end up taking out anyway. > >>>>> > >>>>> 2) I don't like the hiddenness of it since it becomes > especially >>>>> annoying if you have your native in geometry and you > are converting >>>>> to geography for a special usecase, then you end > up with a slower >>>>> implementation >>>>> >>>>> as you would > really end up doing accidentally >>>>> >>>>> geometry -> geography > -> geometry ->operation (and why do I want my >>>>> calcs done in > UTM?) >>>>> >>>>> Instead of the more efficient >>>>> >>>>> > geometry -> operation >>>>> >>>>> Thanks, >>>>> Regina >>>>> > >>>>> -----Original Message----- >>>>> From: > postgis-devel-bounces@... > >>>>> [mailto:postgis-devel-bounces@...] On > Behalf Of >>>>> Paul Ramsey >>>>> Sent: Friday, October 30, 2009 > 8:16 PM >>>>> To: PostGIS Development Discussion >>>>> Subject: > [postgis-devel] Geog/Geom Hack >>>>> >>>>> I'm interested to know > what the general opinion is of the trick I've >>>>> used on >>>>> > ST_Buffer(geography): > >>>>> > >>>>> > >>>>> c > >>>>> #L541 > >>>>> > >>>>> I ask because I could apply the same idea to the larger suite > of OGC >>>>> SFSQL predicates before release. Is half-a-loaf better > than no loaf >>>>> in >>>> this case? > >>>>> (Note that there will be failure cases for really large > geometry, >>>>> like a polygon of "Asia" or "Russia" that have > polygons over the >>>>> dateline.) >>>>> >>>>> P. > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>>> > >>>>> > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >_______________________________________________ > >postgis-devel mailing list > >postgis-devel@... > >http://postgis.refractions.net/mailman/listinfo/postgis-devel > > > > > > > ---------------------------------------------------------------------- > -- > > _______________________________________________ > postgis-users mailing list > postgis-users@... > http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: [postgis-devel] Geog/Geom Hack
by Jose Carlos Martinez
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Hi everyone,
Maybe I did not understand all the chat about Geographic coordinates but if you guys are planning to use geographic coordinates in PostGIS in a wide way then what is going to happen with all the spatial predicates (DE9IM) and the spatial operators based on GEOS/JTS? Please correct me if I am wrong but I think GEOS/JTS are based on 'the shortest line between 2 points is a line so they are using lineal interpolation' and not a geodesic line (sphere or ellipsoid) as we need to work with geographic coordinates. Theses libraries should be rewritten taking into account this fact, dont you think so?..In fact right now if you intersect two lines with GEOS/JTS (geographic coordinates) the result is wrong (even if GEOS had a sphere approach since it would keep being wrong in rigorous point of view). The approach about projecting the geographic coordinates before calling GEOS to a projection with the smallest errors and choosing the right type (equivalent projections, conforming projection) could be the 'only' approach now? Thanks, Jose Carlos Martinez Paragon Corporation wrote: > Nicklas and Paul, > > Yap that's the main point. To add > > I'm not really in disagreement with Paul. I see his point too. I'm > just prodding him to think about all his use cases a little more > because I don't feel he has. > > My feelings to sum up > 1) We have not thought about the complete ramifications of this hack > and I'm really concerned about the novice that transitions to an > expert rather than just getting them hooked on PostGIS. Perhaps I'm > being overly silly with that and even said, Paul's approach might be > an easier to transition solution. > > 2) My concern is the penalty of putting it in and having to take it > out later might be very great (both from a code, testing, as well as > a mindset perspective). I just feel it needs more thought and testing > and really if we want to make our December deadline, I don't want it > rushed in so lightly. > > Unless of course Paul -- you want to wait till January or February to > release 1.5? > > Now the ST_Max_Distance is a separate issue. I would put in the > ST_ConvexHull hack in place. The reason being is that it just > improves performance any way I can think you slice it and an > experienced user would do exactly the same thing always and when > you finally incorporate it into the core function, there is no change > in existing code just a speed improvement. So to me its basically our > ST_DWithin hack -- a very tried and trued obvious answer. Its an > implementation detail with no clear leaky effects. > > With that said, there are some clear functions in geometry that are > safe to put a geography cover over. Those ones where there is clearly > only one answer and don't involve transformation. > > like ST_X, ST_Y etc. That don't require transformation so no screw up > in data. Also observe that even the geometry(geography .... in these > there is no penalty becuase the geometry/geography isn't changing so > the planner can cache the geometry to geography conversion. The > ST_Transformation ones however, the geometry/geography is changing > slightly at each step since ST_Tranformation is a lossy operation so > you are not only incurring overhead (because these answers can't be > cached), but also adding in extra errors . > > To me this is a bleeding abstraction and that is the main reason I > don't like it. > > So getting back to you Paul, > > What functions exactly are you planning to put a veil over? ST_Buffer > well that one is used so much and is not as exact anyway that I > suppose I can grudgingly accept that as okay. > > Thanks, > Regina > > > ------------------------------------------------------------------------ > *From:* postgis-devel-bounces@... > [mailto:postgis-devel-bounces@...] *On Behalf Of > *nicklas.aven@... > *Sent:* Saturday, October 31, 2009 10:04 AM > *To:* PostGIS Development Discussion > *Subject:* Re: [postgis-devel] Geog/Geom Hack > > Hallo > > I can see the points from both of you. I think the most important > argument from you Regina is that it is not transparent enough. A > skillfull user trying postgis might be disapointed when realizing that > the nested functions caused an unnecessary big rounding-error. > But if it is obvious that it is a "special" function at least for the > experienced user knowing about common function-names I don't think it > is a big problem and might work as an easy shortcut at least during > the process of learning. > > As I understand it this could be a solution for using many functions > against geography so, why not note it in the function name like: > ST_tBuffer for transformed buffer. Then when time is to introduse a > "real" variant of the function they can coexist and it will not change > the bahavior inside an application without someone consciously changes > the function name and remove the t. > > the t would be independent of geography-geometry in semantics and just > indicate that it is a lower-precision variant. I fit was commonly used > it would work as a warning to experienced users. > > I have a similar question about st_max_distance. The function gets > very much more effective when ran together with convexhull. I saw the > trick in ST_MinimumBoundingCircle and id makes a big difference to do : > st_max_distance(st_convexhull(the_geom)) instead of just > st_max_distance(the_geom). > The question is: Should that be put in the sql-function? > My opinion now is that we just tell about it in the documentation and > aims at doing that trick internally in C in the future. Maybe together > with moving the whole convexhull to postgis-native from geos. It > didn't look that impossible fromthe JTS-code. > > /Nicklas > > > 2009-10-31 Paul Ramsey wrote: > > I still think I'm right :) Honestly, I've got to a lot of trouble to > >make this stuff for newbies, and I don't think "learn how it works" is > >the right answer for them. They had that option before, but taking GIS > >101 is not an option for these people, they need something that "just > >works". It's easier to teach the experienced people the pitfalls than > >the inexperienced people the basics. > > > >BTW, I just upgraded distance_sphere and distance_spheroid to be as > >powerful (handling point/line/polygon) as the geography variants, > >removing excuses for transforming geometries into geographies for > >processing purposes. > > > >P. > > > >On Fri, Oct 30, 2009 at 9:15 PM, Paragon Corporation wrote: > >> Paul, > >> For what its worth, here is another reason why I don't like this > idea and I > >> think we should at least think about its ramifications more so > should put it > >> off for consideration until 2.0. > >> > >> In geometry processing, its common practice to apply a lot of > functions in > >> succession > >> > >> process1(process2(process3(geometry/geography) > >> > >> With your hackish approach -- the unsuspecting novice user will be > incurring > >> a lot of transformation rounding errors with each process > >> > >> The advanced user, won't know if this is okay or not -- because > they can't > >> tell by looking at the function call the hidden transformations > going on. > >> > >> If these did not exist, they would transform once before the > processes and > >> once after) and incurr much less penalty > >> > >> But if they both exist, they will treat them as being on equal footing > >> > >> ST_Buffer(geometry) and ST_Buffer(geography) > >> > >> > >> So your approach while well-meaning gives a questionable benefit to > novices > >> and is putting experienced users at a disadvantage. > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf Of > Paragon > >> Corporation > >> Sent: Friday, October 30, 2009 11:54 PM > >> To: 'PostGIS Development Discussion' > >> Cc: 'PostGIS Users Discussion' > >> Subject: Re: [postgis-devel] Geog/Geom Hack > >> > >> Paul, > >> I suppose we can't just put this decision off till 2.0. Isn't this > a bit of > >> scope creep? I'm not absolutely sure which way is better, but I > know the > >> cost of rolling back the change is more. > >> > >> If you are going to do this, how many functions are you planning to > do this > >> for? > >> > >> I'm cc'ing the postgis users group too to get more of an opinion on > this > >> topic. > >> > >> So the question is it it a good idea to introduce a hack that > transforms a > >> geography into what we call BestSRID to perform geometry operations > on and > >> then transform back. My concern is that this is a silent operation > that > >> gives the impression that these functions are natively done in spheroid > >> space just for the benefit of catering to less technical users. > >> > >> > http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.c#L541 > >> > >> So you can't really tell by looking the penalty > >> > >> Main examples of this as shown for ST_Buffer > >> > >> CREATE OR REPLACE FUNCTION _ST_BestSRID(geography, geography) > >> 530 RETURNS integer > >> 531 AS 'MODULE_PATHNAME','geography_bestsrid' > >> 532 LANGUAGE 'C' IMMUTABLE STRICT; > >> 533 > >> 534 -- Availability: 1.5.0 > >> 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) > >> 536 RETURNS integer > >> 537 AS 'SELECT _ST_BestSRID($1,$1)' > >> 538 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 539 > >> 540 -- Availability: 1.5.0 > >> 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) > >> 542 RETURNS geography > >> 543 AS 'SELECT > >> geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), > >> _ST_BestSRID($1)), $2), 4326))' > >> 544 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 545 > >> > >> > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf Of > Paul > >> Ramsey > >> Sent: Friday, October 30, 2009 11:07 PM > >> To: PostGIS Development Discussion > >> Subject: Re: [postgis-devel] Geog/Geom Hack > >> > >> We're going to have to agree to disagree on this one, Regina. > Catering to > >> the less technical users is what this exercise is all about, to my > mind, and > >> that includes allowing easy flipping into geometry for calculations > that > >> aren't supported in geography yet. Oracle does this too. > >> > >> What do other folks think? > >> > >> P. > >> > >> On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation wrote: > >>> Paul, > >>> Hmm when I am comparing distance of two geometries in different > >>> spatial refs which I do a lot. > >>> > >>> I still don't like the hack even if you disregard the above or if you > >>> must hack -- don't give it the same name as the non-hacked functions. > >>> > >>> the whole idea of picking BestSRID for a person to cater to less > >>> technical users I find extremely annoying as I can think of 20 > >>> "BestSRID" depending on what I am doing. If they get to that level of > >>> sophistication, I would rather have them think a little more and > >>> understand the implications of those decisions. > >>> > >>> We must learn to crawl before we can learn to walk,because walking > >>> without understanding will just get you into trouble in the long run. > >>> > >>> > >>> Thanks, > >>> Regina > >>> > >>> -----Original Message----- > >>> From: postgis-devel-bounces@... > >>> [mailto:postgis-devel-bounces@...] On Behalf Of > >>> Paul Ramsey > >>> Sent: Friday, October 30, 2009 9:47 PM > >>> To: PostGIS Development Discussion > >>> Subject: Re: [postgis-devel] Geog/Geom Hack > >>> > >>> You *can*, but I strongly doubt you *will*. Because there's nothing in > >>> geography that isn't already in geometry. So you as a primary geometry > >>> user are going to have no working need to cast things to geography. > >>> > >>> On the other hand, the very first question from users of geography > >>> will be "how can I access ?" So having a > >>> relatively full set of functions already available in geography makes > >>> sense to me, even if they are hacked in with a planar trick. > >>> > >>> P. > >>> > >>> On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation wrote: > >>>> Paul, > >>>> I can put a functional geography index on can't I and take advantage > >>>> of geography index bindings? > >>>> > >>>> Lets say I have a large network of tables broken out by region so I > >>>> know a specific table has one srid. > >>>> > >>>> For many queries, I may go to that table directly or if I'm doing > >>>> single geometry processing, really don't care what srid as long as > >>>> its in utm or whatever - so I can use the full power of GEOS. > >>>> > >>>> For my across the board distance checks and so forth, I would want to > >>>> use geography and I could use a geography index if I put a functional > >>>> geography index on my geometry correct? Though that needs some more > >>> testing. > >>>> > >>>> > >>>> So in short if 90% of my workload involves geometry processing, I > >>>> will want to keep my data in geometry > >>>> > >>>> But the 10% I would want to convert to geography on the fly. > >>>> > >>>> Thanks, > >>>> Regina > >>>> > >>>> -----Original Message----- > >>>> From: postgis-devel-bounces@... > >>>> [mailto:postgis-devel-bounces@...] On Behalf Of > >>>> Paul Ramsey > >>>> Sent: Friday, October 30, 2009 8:34 PM > >>>> To: PostGIS Development Discussion > >>>> Subject: Re: [postgis-devel] Geog/Geom Hack > >>>> > >>>> I'm not sure I understand why you would ever convert a geometry to a > >>>> geography as part of a query on a geometry table. I fully expect > >>>> geography to be used as a storage type, because of the utility of > >>>> having the correct spherical indexes, which are not available when > >>>> you're just converting in via a cast. Since there's no functions > >>>> available on geography that are not already available on geometry, > >>>> why would you ever do a geometry->geography cast unless you are (a) > >>>> testing geography or (b) bulk converting a table into geography for > >>> storage in that type. > >>>> > >>>> P. > >>>> > >>>> > >>>> > >>>> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation wrote: > >>>>> Paul, > >>>>> I would rather you didn't for 2 reasons > >>>>> > >>>>> 1) I'm lazy and for each of these things we'd have to apply the text > >>>>> additional function proto hack to prevent from it breaking geometry. > >>>>> which we will probably end up taking out anyway. > >>>>> > >>>>> 2) I don't like the hiddenness of it since it becomes especially > >>>>> annoying if you have your native in geometry and you are converting > >>>>> to geography for a special usecase, then you end up with a slower > >>>>> implementation > >>>>> > >>>>> as you would really end up doing accidentally > >>>>> > >>>>> geometry -> geography -> geometry ->operation (and why do I want my > >>>>> calcs done in UTM?) > >>>>> > >>>>> Instead of the more efficient > >>>>> > >>>>> geometry -> operation > >>>>> > >>>>> Thanks, > >>>>> Regina > >>>>> > >>>>> -----Original Message----- > >>>>> From: postgis-devel-bounces@... > >>>>> [mailto:postgis-devel-bounces@...] On Behalf Of > >>>>> Paul Ramsey > >>>>> Sent: Friday, October 30, 2009 8:16 PM > >>>>> To: PostGIS Development Discussion > >>>>> Subject: [postgis-devel] Geog/Geom Hack > >>>>> > >>>>> I'm interested to know what the general opinion is of the trick I've > >>>>> used on > >>>>> ST_Buffer(geography): > >>>>> > >>>>> > http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in. > >>>>> c > >>>>> #L541 > >>>>> > >>>>> I ask because I could apply the same idea to the larger suite of OGC > >>>>> SFSQL predicates before release. Is half-a-loaf better than no loaf > >>>>> in > >>>> this case? > >>>>> (Note that there will be failure cases for really large geometry, > >>>>> like a polygon of "Asia" or "Russia" that have polygons over the > >>>>> dateline.) > >>>>> > >>>>> P. > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>>> > >>>>> > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >_______________________________________________ > >postgis-devel mailing list > >postgis-devel@... > >http://postgis.refractions.net/mailman/listinfo/postgis-devel > > > > > ------------------------------------------------------------------------ > > _______________________________________________ > postgis-users mailing list > postgis-users@... > http://postgis.refractions.net/mailman/listinfo/postgis-users > -- ------------------------------ José Carlos Martínez Llario Producción Cartográfica y SIG. Dpto. Ingeniería Cartográfica. Univ. Politécnica de Valencia. E-mail: jomarlla@... Telf: 963877007 ext. 75599 ------------------------------ _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: [postgis-devel] Geog/Geom Hack
by Paragon Corporation-2
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Jose,
Paul can answer this better than I can. right now the functions we have published for geodetic (ST_Length, ST_Distance, AT_Area etc) do not use shortest line along a plane like GEOS/JTS or current PostGIS distance etc. -- they are genuinely measuring along a sphere/spheroid. So the only issue we are talking about as you said is the cases where we don't have a true geodetic answer for right now. Paul's approach is to find the best spatial ref for it (whatever that means?) -- transform it to that and then do the JTS/GEOS operations and to pass this off as a correct answer. My point is yes that's generally the right thing to do, but not always - it becomes wrong depending on how big of a thing you are talking about (and the both good and bad thing about geography is that you can be talking about bigger things than you can easily with a correct planar) . So while having these functions makes peoples lives easier -- it also makes them difficult, because now you can't distinguish the really good functions we have designed specifically for sphere/spheroid from these hackish estimates. No novice or advanced user would be able to do this without constantly referring to the docs. How relevant this is to know is my question? Thus came the other solution of just naming them differently that Nicklas proposed so one can tell by the name that these are doing some questionable (and possibly costly) things behind the scenes. Thanks, Regina -----Original Message----- From: postgis-users-bounces@... [mailto:postgis-users-bounces@...] On Behalf Of Jose Carlos Martinez Llario Sent: Saturday, October 31, 2009 12:34 PM To: PostGIS Users Discussion Subject: Re: [postgis-users] [postgis-devel] Geog/Geom Hack Hi everyone, Maybe I did not understand all the chat about Geographic coordinates but if you guys are planning to use geographic coordinates in PostGIS in a wide way then what is going to happen with all the spatial predicates (DE9IM) and the spatial operators based on GEOS/JTS? Please correct me if I am wrong but I think GEOS/JTS are based on 'the shortest line between 2 points is a line so they are using lineal interpolation' and not a geodesic line (sphere or ellipsoid) as we need to work with geographic coordinates. Theses libraries should be rewritten taking into account this fact, dont you think so?..In fact right now if you intersect two lines with GEOS/JTS (geographic coordinates) the result is wrong (even if GEOS had a sphere approach since it would keep being wrong in rigorous point of view). The approach about projecting the geographic coordinates before calling GEOS to a projection with the smallest errors and choosing the right type (equivalent projections, conforming projection) could be the 'only' approach now? Thanks, Jose Carlos Martinez Paragon Corporation wrote: > Nicklas and Paul, > > Yap that's the main point. To add > > I'm not really in disagreement with Paul. I see his point too. I'm > just prodding him to think about all his use cases a little more > because I don't feel he has. > > My feelings to sum up > 1) We have not thought about the complete ramifications of this hack > and I'm really concerned about the novice that transitions to an > expert rather than just getting them hooked on PostGIS. Perhaps I'm > being overly silly with that and even said, Paul's approach might be > an easier to transition solution. > > 2) My concern is the penalty of putting it in and having to take it > out later might be very great (both from a code, testing, as well as > a mindset perspective). I just feel it needs more thought and testing > and really if we want to make our December deadline, I don't want it > rushed in so lightly. > > Unless of course Paul -- you want to wait till January or February to > release 1.5? > > Now the ST_Max_Distance is a separate issue. I would put in the > ST_ConvexHull hack in place. The reason being is that it just > improves performance any way I can think you slice it and an > experienced user would do exactly the same thing always and when you > finally incorporate it into the core function, there is no change in > existing code just a speed improvement. So to me its basically our > ST_DWithin hack -- a very tried and trued obvious answer. Its an > implementation detail with no clear leaky effects. > > With that said, there are some clear functions in geometry that are > safe to put a geography cover over. Those ones where there is clearly > only one answer and don't involve transformation. > > like ST_X, ST_Y etc. That don't require transformation so no screw up > in data. Also observe that even the geometry(geography .... in these > there is no penalty becuase the geometry/geography isn't changing so > the planner can cache the geometry to geography conversion. The > ST_Transformation ones however, the geometry/geography is changing > slightly at each step since ST_Tranformation is a lossy operation so > you are not only incurring overhead (because these answers can't be > cached), but also adding in extra errors . > > To me this is a bleeding abstraction and that is the main reason I > don't like it. > > So getting back to you Paul, > > What functions exactly are you planning to put a veil over? ST_Buffer > well that one is used so much and is not as exact anyway that I > suppose I can grudgingly accept that as okay. > > Thanks, > Regina > > > ---------------------------------------------------------------------- > -- > *From:* postgis-devel-bounces@... > [mailto:postgis-devel-bounces@...] *On Behalf Of > *nicklas.aven@... > *Sent:* Saturday, October 31, 2009 10:04 AM > *To:* PostGIS Development Discussion > *Subject:* Re: [postgis-devel] Geog/Geom Hack > > Hallo > > I can see the points from both of you. I think the most important > argument from you Regina is that it is not transparent enough. A > skillfull user trying postgis might be disapointed when realizing that > the nested functions caused an unnecessary big rounding-error. > But if it is obvious that it is a "special" function at least for the > experienced user knowing about common function-names I don't think it > is a big problem and might work as an easy shortcut at least during > the process of learning. > > As I understand it this could be a solution for using many functions > against geography so, why not note it in the function name like: > ST_tBuffer for transformed buffer. Then when time is to introduse a > "real" variant of the function they can coexist and it will not change > the bahavior inside an application without someone consciously changes > the function name and remove the t. > > the t would be independent of geography-geometry in semantics and just > indicate that it is a lower-precision variant. I fit was commonly used > it would work as a warning to experienced users. > > I have a similar question about st_max_distance. The function gets > very much more effective when ran together with convexhull. I saw the > trick in ST_MinimumBoundingCircle and id makes a big difference to do : > st_max_distance(st_convexhull(the_geom)) instead of just > st_max_distance(the_geom). > The question is: Should that be put in the sql-function? > My opinion now is that we just tell about it in the documentation and > aims at doing that trick internally in C in the future. Maybe together > with moving the whole convexhull to postgis-native from geos. It > didn't look that impossible fromthe JTS-code. > > /Nicklas > > > 2009-10-31 Paul Ramsey wrote: > > I still think I'm right :) Honestly, I've got to a lot of trouble to > >make this stuff for newbies, and I don't think "learn how it works" > >is the right answer for them. They had that option before, but taking > >GIS > >101 is not an option for these people, they need something that "just > >works". It's easier to teach the experienced people the pitfalls than > >the inexperienced people the basics. > > > >BTW, I just upgraded distance_sphere and distance_spheroid to be as > >powerful (handling point/line/polygon) as the geography variants, > >removing excuses for transforming geometries into geographies for > >processing purposes. > > > >P. > > > >On Fri, Oct 30, 2009 at 9:15 PM, Paragon Corporation wrote: > >> Paul, > >> For what its worth, here is another reason why I don't like this > idea and I > >> think we should at least think about its ramifications more so > should put it > >> off for consideration until 2.0. > >> > >> In geometry processing, its common practice to apply a lot of > functions in > >> succession > >> > >> process1(process2(process3(geometry/geography) > >> > >> With your hackish approach -- the unsuspecting novice user will be > incurring > >> a lot of transformation rounding errors with each process > >> > >> The advanced user, won't know if this is okay or not -- because > they can't > >> tell by looking at the function call the hidden transformations > going on. > >> > >> If these did not exist, they would transform once before the > processes and > >> once after) and incurr much less penalty > >> > >> But if they both exist, they will treat them as being on equal > >> footing > >> > >> ST_Buffer(geometry) and ST_Buffer(geography) > >> > >> > >> So your approach while well-meaning gives a questionable benefit to > novices > >> and is putting experienced users at a disadvantage. > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf Of > Paragon > >> Corporation > >> Sent: Friday, October 30, 2009 11:54 PM > >> To: 'PostGIS Development Discussion' > >> Cc: 'PostGIS Users Discussion' > >> Subject: Re: [postgis-devel] Geog/Geom Hack > >> > >> Paul, > >> I suppose we can't just put this decision off till 2.0. Isn't this > a bit of > >> scope creep? I'm not absolutely sure which way is better, but I > know the > >> cost of rolling back the change is more. > >> > >> If you are going to do this, how many functions are you planning to > do this > >> for? > >> > >> I'm cc'ing the postgis users group too to get more of an opinion on > this > >> topic. > >> > >> So the question is it it a good idea to introduce a hack that > transforms a > >> geography into what we call BestSRID to perform geometry operations > on and > >> then transform back. My concern is that this is a silent operation > that > >> gives the impression that these functions are natively done in > >> spheroid space just for the benefit of catering to less technical > >> > >> > http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.c > #L541 > >> > >> So you can't really tell by looking the penalty > >> > >> Main examples of this as shown for ST_Buffer > >> > >> CREATE OR REPLACE FUNCTION _ST_BestSRID(geography, geography) > >> 530 RETURNS integer > >> 531 AS 'MODULE_PATHNAME','geography_bestsrid' > >> 532 LANGUAGE 'C' IMMUTABLE STRICT; > >> 533 > >> 534 -- Availability: 1.5.0 > >> 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) > >> 536 RETURNS integer > >> 537 AS 'SELECT _ST_BestSRID($1,$1)' > >> 538 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 539 > >> 540 -- Availability: 1.5.0 > >> 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) > >> 542 RETURNS geography > >> 543 AS 'SELECT > >> geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), > >> _ST_BestSRID($1)), $2), 4326))' > >> 544 LANGUAGE 'SQL' IMMUTABLE STRICT; > >> 545 > >> > >> > >> > >> Thanks, > >> Regina > >> > >> -----Original Message----- > >> From: postgis-devel-bounces@... > >> [mailto:postgis-devel-bounces@...] On Behalf Of > Paul > >> Ramsey > >> Sent: Friday, October 30, 2009 11:07 PM > >> To: PostGIS Development Discussion > >> Subject: Re: [postgis-devel] Geog/Geom Hack > >> > >> We're going to have to agree to disagree on this one, Regina. > Catering to > >> the less technical users is what this exercise is all about, to my > mind, and > >> that includes allowing easy flipping into geometry for calculations > that > >> aren't supported in geography yet. Oracle does this too. > >> > >> What do other folks think? > >> > >> P. > >> > >> On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation wrote: > >>> Paul, > >>> Hmm when I am comparing distance of two geometries in different > >>> spatial refs which I do a lot. > >>> > >>> I still don't like the hack even if you disregard the above or if > >>> you must hack -- don't give it the same name as the non-hacked > >>> > >>> the whole idea of picking BestSRID for a person to cater to less > >>> technical users I find extremely annoying as I can think of 20 > >>> "BestSRID" depending on what I am doing. If they get to that > >>> level of sophistication, I would rather have them think a little > >>> more and understand the implications of those decisions. > >>> > >>> We must learn to crawl before we can learn to walk,because walking > >>> without understanding will just get you into trouble in the long run. > >>> > >>> > >>> Thanks, > >>> Regina > >>> > >>> -----Original Message----- > >>> From: postgis-devel-bounces@... > >>> [mailto:postgis-devel-bounces@...] On Behalf > >>> Of Paul Ramsey > >>> Sent: Friday, October 30, 2009 9:47 PM > >>> To: PostGIS Development Discussion > >>> Subject: Re: [postgis-devel] Geog/Geom Hack > >>> > >>> You *can*, but I strongly doubt you *will*. Because there's > >>> nothing in geography that isn't already in geometry. So you as a > >>> primary geometry user are going to have no working need to cast things > >>> > >>> On the other hand, the very first question from users of geography > >>> will be "how can I access ?" So having a relatively full set of > >>> functions already available in geography makes sense to me, even > >>> if they are hacked in with a planar trick. > >>> > >>> P. > >>> > >>> On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation wrote: > >>>> Paul, > >>>> I can put a functional geography index on can't I and take > >>>> advantage of geography index bindings? > >>>> > >>>> Lets say I have a large network of tables broken out by region so > >>>> I know a specific table has one srid. > >>>> > >>>> For many queries, I may go to that table directly or if I'm doing > >>>> single geometry processing, really don't care what srid as long > >>>> as its in utm or whatever - so I can use the full power of GEOS. > >>>> > >>>> For my across the board distance checks and so forth, I would > >>>> want to use geography and I could use a geography index if I put > >>>> a functional geography index on my geometry correct? Though that > >>>> needs some more > >>> testing. > >>>> > >>>> > >>>> So in short if 90% of my workload involves geometry processing, I > >>>> will want to keep my data in geometry > >>>> > >>>> But the 10% I would want to convert to geography on the fly. > >>>> > >>>> Thanks, > >>>> Regina > >>>> > >>>> -----Original Message----- > >>>> From: postgis-devel-bounces@... > >>>> [mailto:postgis-devel-bounces@...] On Behalf > >>>> Of Paul Ramsey > >>>> Sent: Friday, October 30, 2009 8:34 PM > >>>> To: PostGIS Development Discussion > >>>> Subject: Re: [postgis-devel] Geog/Geom Hack > >>>> > >>>> I'm not sure I understand why you would ever convert a geometry > >>>> to a geography as part of a query on a geometry table. I fully > >>>> expect geography to be used as a storage type, because of the > >>>> utility of having the correct spherical indexes, which are not > >>>> available when you're just converting in via a cast. Since > >>>> there's no functions available on geography that are not already > >>>> available on geometry, why would you ever do a > >>>> geometry->geography cast unless you are (a) testing geography or > >>>> (b) bulk converting a table into geography for > >>> storage in that type. > >>>> > >>>> P. > >>>> > >>>> > >>>> > >>>> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation wrote: > >>>>> Paul, > >>>>> I would rather you didn't for 2 reasons > >>>>> > >>>>> 1) I'm lazy and for each of these things we'd have to apply the > >>>>> text additional function proto hack to prevent from it breaking > >>>>> which we will probably end up taking out anyway. > >>>>> > >>>>> 2) I don't like the hiddenness of it since it becomes especially > >>>>> annoying if you have your native in geometry and you are > >>>>> converting to geography for a special usecase, then you end up > >>>>> with a slower implementation > >>>>> > >>>>> as you would really end up doing accidentally > >>>>> > >>>>> geometry -> geography -> geometry ->operation (and why do I want > >>>>> my calcs done in UTM?) > >>>>> > >>>>> Instead of the more efficient > >>>>> > >>>>> geometry -> operation > >>>>> > >>>>> Thanks, > >>>>> Regina > >>>>> > >>>>> -----Original Message----- > >>>>> From: postgis-devel-bounces@... > >>>>> [mailto:postgis-devel-bounces@...] On Behalf > >>>>> Of Paul Ramsey > >>>>> Sent: Friday, October 30, 2009 8:16 PM > >>>>> To: PostGIS Development Discussion > >>>>> Subject: [postgis-devel] Geog/Geom Hack > >>>>> > >>>>> I'm interested to know what the general opinion is of the trick > >>>>> I've used on > >>>>> ST_Buffer(geography): > >>>>> > >>>>> > http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in. > >>>>> c > >>>>> #L541 > >>>>> > >>>>> I ask because I could apply the same idea to the larger suite of > >>>>> OGC SFSQL predicates before release. Is half-a-loaf better than > >>>>> no loaf in > >>>> this case? > >>>>> (Note that there will be failure cases for really large > >>>>> geometry, like a polygon of "Asia" or "Russia" that have > >>>>> polygons over the > >>>>> dateline.) > >>>>> > >>>>> P. > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>>> > >>>>> > >>>>> _______________________________________________ > >>>>> postgis-devel mailing list > >>>>> postgis-devel@... > >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> postgis-devel mailing list > >>>> postgis-devel@... > >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >>> > >>> _______________________________________________ > >>> postgis-devel mailing list > >>> postgis-devel@... > >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >>> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >> > >> _______________________________________________ > >> postgis-devel mailing list > >> postgis-devel@... > >> http://postgis.refractions.net/mailman/listinfo/postgis-devel > >> > >_______________________________________________ > >postgis-devel mailing list > >postgis-devel@... > >http://postgis.refractions.net/mailman/listinfo/postgis-devel > > > > > ---------------------------------------------------------------------- > -- > > _______________________________________________ > postgis-users mailing list > postgis-users@... > http://postgis.refractions.net/mailman/listinfo/postgis-users > -- ------------------------------ José Carlos Martínez Llario Producción Cartográfica y SIG. Dpto. Ingeniería Cartográfica. Univ. Politécnica de Valencia. E-mail: jomarlla@... Telf: 963877007 ext. 75599 ------------------------------ _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: [postgis-devel] Geog/Geom Hack
by Jose Carlos Martinez
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Thanks a lot Regina as you said it can be so confusing for users.
I understood now the problem you guys are talking about. But I would like to go back again to the geodetic problem with not trivial method (ST_Intersects..., ST_Intersection.., etc.) I am reading the OGC 06-103r3 now..and for example OGC says in buffer: "Becaose of the limitations of linear interpolation, there will often be some relatively small error in this distance" They extends too this comment in general to any geometry operation so they are assuming that So I think they admit small errors (I do not how big..), anyways they talk just about LINEAR interpolation. Maybe the OGC didnt think a lot about geographic coordinates when they wrote this specifications or maybe they are working in other specifications right now...no idea.. Anyways if PostGIS transforms the coordinates from geographic to some projection before calling GEOS..then I think PostGIS/GEOS should use some coordinate tolerance inside the spatial operators and predicates, otherwise geometries that intersect, overlap, etc in the real world (real world is the ellipsoid or at least sphere) are not going to intersect, overlap,etc. in projected coordinates. Thanx, Best, Jose Paragon Corporation wrote: > Jose, > > Paul can answer this better than I can. > > right now the functions we have published for geodetic (ST_Length, > ST_Distance, AT_Area etc) do not use shortest line along a plane like > GEOS/JTS or current PostGIS distance etc. -- they are genuinely measuring > along a sphere/spheroid. > > So the only issue we are talking about as you said is the cases where we > don't have a true geodetic answer for right now. > > Paul's approach is to find the best spatial ref for it (whatever that > means?) -- transform it to that and then do the JTS/GEOS operations and to > pass this off as a correct answer. > > My point is yes that's generally the right thing to do, but not always - it > becomes wrong depending on how big of a thing you are talking about (and the > both good and bad thing about geography is that you can be talking about > bigger things than you can easily with a correct planar) . So while having > these functions makes peoples lives easier -- it also makes them difficult, > because now you can't distinguish the really good functions we have designed > specifically for sphere/spheroid from these hackish estimates. No novice or > advanced user would be able to do this without constantly referring to the > docs. How relevant this is to know is my question? > > Thus came the other solution of just naming them differently that Nicklas > proposed so one can tell by the name that these are doing some questionable > (and possibly costly) things behind the scenes. > > Thanks, > Regina > > > > -----Original Message----- > From: postgis-users-bounces@... > [mailto:postgis-users-bounces@...] On Behalf Of Jose > Carlos Martinez Llario > Sent: Saturday, October 31, 2009 12:34 PM > To: PostGIS Users Discussion > Subject: Re: [postgis-users] [postgis-devel] Geog/Geom Hack > > Hi everyone, > Maybe I did not understand all the chat about Geographic coordinates but if > you guys are planning to use geographic coordinates in PostGIS in a wide way > then what is going to happen with all the spatial predicates > (DE9IM) and the spatial operators based on GEOS/JTS? > > Please correct me if I am wrong but I think GEOS/JTS are based on 'the > shortest line between 2 points is a line so they are using lineal > interpolation' and not a geodesic line (sphere or ellipsoid) as we need to > work with geographic coordinates. Theses libraries should be rewritten > taking into account this fact, dont you think so?..In fact right now if you > intersect two lines with GEOS/JTS (geographic > coordinates) the result is wrong (even if GEOS had a sphere approach since > it would keep being wrong in rigorous point of view). > > The approach about projecting the geographic coordinates before calling GEOS > to a projection with the smallest errors and choosing the right type > (equivalent projections, conforming projection) could be the 'only' > approach now? > > Thanks, > Jose Carlos Martinez > > > > > Paragon Corporation wrote: > >> Nicklas and Paul, >> >> Yap that's the main point. To add >> >> I'm not really in disagreement with Paul. I see his point too. I'm >> just prodding him to think about all his use cases a little more >> because I don't feel he has. >> >> My feelings to sum up >> 1) We have not thought about the complete ramifications of this hack >> and I'm really concerned about the novice that transitions to an >> expert rather than just getting them hooked on PostGIS. Perhaps I'm >> being overly silly with that and even said, Paul's approach might be >> an easier to transition solution. >> >> 2) My concern is the penalty of putting it in and having to take it >> out later might be very great (both from a code, testing, as well as >> a mindset perspective). I just feel it needs more thought and testing >> and really if we want to make our December deadline, I don't want it >> rushed in so lightly. >> >> Unless of course Paul -- you want to wait till January or February to >> release 1.5? >> >> Now the ST_Max_Distance is a separate issue. I would put in the >> ST_ConvexHull hack in place. The reason being is that it just >> improves performance any way I can think you slice it and an >> experienced user would do exactly the same thing always and when you >> finally incorporate it into the core function, there is no change in >> existing code just a speed improvement. So to me its basically our >> ST_DWithin hack -- a very tried and trued obvious answer. Its an >> implementation detail with no clear leaky effects. >> >> With that said, there are some clear functions in geometry that are >> safe to put a geography cover over. Those ones where there is clearly >> only one answer and don't involve transformation. >> >> like ST_X, ST_Y etc. That don't require transformation so no screw up >> in data. Also observe that even the geometry(geography .... in these >> there is no penalty becuase the geometry/geography isn't changing so >> the planner can cache the geometry to geography conversion. The >> ST_Transformation ones however, the geometry/geography is changing >> slightly at each step since ST_Tranformation is a lossy operation so >> you are not only incurring overhead (because these answers can't be >> cached), but also adding in extra errors . >> >> To me this is a bleeding abstraction and that is the main reason I >> don't like it. >> >> So getting back to you Paul, >> >> What functions exactly are you planning to put a veil over? ST_Buffer >> well that one is used so much and is not as exact anyway that I >> suppose I can grudgingly accept that as okay. >> >> Thanks, >> Regina >> >> >> ---------------------------------------------------------------------- >> -- >> *From:* postgis-devel-bounces@... >> [mailto:postgis-devel-bounces@...] *On Behalf Of >> *nicklas.aven@... >> *Sent:* Saturday, October 31, 2009 10:04 AM >> *To:* PostGIS Development Discussion >> *Subject:* Re: [postgis-devel] Geog/Geom Hack >> >> Hallo >> >> I can see the points from both of you. I think the most important >> argument from you Regina is that it is not transparent enough. A >> skillfull user trying postgis might be disapointed when realizing that >> the nested functions caused an unnecessary big rounding-error. >> But if it is obvious that it is a "special" function at least for the >> experienced user knowing about common function-names I don't think it >> is a big problem and might work as an easy shortcut at least during >> the process of learning. >> >> As I understand it this could be a solution for using many functions >> against geography so, why not note it in the function name like: >> ST_tBuffer for transformed buffer. Then when time is to introduse a >> "real" variant of the function they can coexist and it will not change >> the bahavior inside an application without someone consciously changes >> > > >> the function name and remove the t. >> >> the t would be independent of geography-geometry in semantics and just >> indicate that it is a lower-precision variant. I fit was commonly used >> it would work as a warning to experienced users. >> >> I have a similar question about st_max_distance. The function gets >> very much more effective when ran together with convexhull. I saw the >> trick in ST_MinimumBoundingCircle and id makes a big difference to do : >> st_max_distance(st_convexhull(the_geom)) instead of just >> st_max_distance(the_geom). >> The question is: Should that be put in the sql-function? >> My opinion now is that we just tell about it in the documentation and >> aims at doing that trick internally in C in the future. Maybe together >> with moving the whole convexhull to postgis-native from geos. It >> didn't look that impossible fromthe JTS-code. >> >> /Nicklas >> >> >> 2009-10-31 Paul Ramsey wrote: >> >> I still think I'm right :) Honestly, I've got to a lot of trouble to >> >>> make this stuff for newbies, and I don't think "learn how it works" >>> is the right answer for them. They had that option before, but taking >>> GIS >>> 101 is not an option for these people, they need something that "just >>> works". It's easier to teach the experienced people the pitfalls than >>> the inexperienced people the basics. >>> >>> BTW, I just upgraded distance_sphere and distance_spheroid to be as >>> powerful (handling point/line/polygon) as the geography variants, >>> removing excuses for transforming geometries into geographies for >>> processing purposes. >>> >>> P. >>> >>> On Fri, Oct 30, 2009 at 9:15 PM, Paragon Corporation wrote: >>> >>>> Paul, >>>> For what its worth, here is another reason why I don't like this >>>> >> idea and I >> >>>> think we should at least think about its ramifications more so >>>> >> should put it >> >>>> off for consideration until 2.0. >>>> >>>> In geometry processing, its common practice to apply a lot of >>>> >> functions in >> >>>> succession >>>> >>>> process1(process2(process3(geometry/geography) >>>> >>>> With your hackish approach -- the unsuspecting novice user will be >>>> >> incurring >> >>>> a lot of transformation rounding errors with each process >>>> >>>> The advanced user, won't know if this is okay or not -- because >>>> >> they can't >> >>>> tell by looking at the function call the hidden transformations >>>> >> going on. >> >>>> If these did not exist, they would transform once before the >>>> >> processes and >> >>>> once after) and incurr much less penalty >>>> >>>> But if they both exist, they will treat them as being on equal >>>> footing >>>> >>>> ST_Buffer(geometry) and ST_Buffer(geography) >>>> >>>> >>>> So your approach while well-meaning gives a questionable benefit to >>>> >> novices >> >>>> and is putting experienced users at a disadvantage. >>>> >>>> Thanks, >>>> Regina >>>> >>>> -----Original Message----- >>>> From: postgis-devel-bounces@... >>>> [mailto:postgis-devel-bounces@...] On Behalf Of >>>> >> Paragon >> >>>> Corporation >>>> Sent: Friday, October 30, 2009 11:54 PM >>>> To: 'PostGIS Development Discussion' >>>> Cc: 'PostGIS Users Discussion' >>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>> >>>> Paul, >>>> I suppose we can't just put this decision off till 2.0. Isn't this >>>> >> a bit of >> >>>> scope creep? I'm not absolutely sure which way is better, but I >>>> >> know the >> >>>> cost of rolling back the change is more. >>>> >>>> If you are going to do this, how many functions are you planning to >>>> >> do this >> >>>> for? >>>> >>>> I'm cc'ing the postgis users group too to get more of an opinion on >>>> >> this >> >>>> topic. >>>> >>>> So the question is it it a good idea to introduce a hack that >>>> >> transforms a >> >>>> geography into what we call BestSRID to perform geometry operations >>>> >> on and >> >>>> then transform back. My concern is that this is a silent operation >>>> >> that >> >>>> gives the impression that these functions are natively done in >>>> spheroid space just for the benefit of catering to less technical >>>> > users. > >>>> >> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.c >> #L541 >> >>>> So you can't really tell by looking the penalty >>>> >>>> Main examples of this as shown for ST_Buffer >>>> >>>> CREATE OR REPLACE FUNCTION _ST_BestSRID(geography, geography) >>>> 530 RETURNS integer >>>> 531 AS 'MODULE_PATHNAME','geography_bestsrid' >>>> 532 LANGUAGE 'C' IMMUTABLE STRICT; >>>> 533 >>>> 534 -- Availability: 1.5.0 >>>> 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) >>>> 536 RETURNS integer >>>> 537 AS 'SELECT _ST_BestSRID($1,$1)' >>>> 538 LANGUAGE 'SQL' IMMUTABLE STRICT; >>>> 539 >>>> 540 -- Availability: 1.5.0 >>>> 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) >>>> 542 RETURNS geography >>>> 543 AS 'SELECT >>>> geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), >>>> _ST_BestSRID($1)), $2), 4326))' >>>> 544 LANGUAGE 'SQL' IMMUTABLE STRICT; >>>> 545 >>>> >>>> >>>> >>>> Thanks, >>>> Regina >>>> >>>> -----Original Message----- >>>> From: postgis-devel-bounces@... >>>> [mailto:postgis-devel-bounces@...] On Behalf Of >>>> >> Paul >> >>>> Ramsey >>>> Sent: Friday, October 30, 2009 11:07 PM >>>> To: PostGIS Development Discussion >>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>> >>>> We're going to have to agree to disagree on this one, Regina. >>>> >> Catering to >> >>>> the less technical users is what this exercise is all about, to my >>>> >> mind, and >> >>>> that includes allowing easy flipping into geometry for calculations >>>> >> that >> >>>> aren't supported in geography yet. Oracle does this too. >>>> >>>> What do other folks think? >>>> >>>> P. >>>> >>>> On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation wrote: >>>> >>>>> Paul, >>>>> Hmm when I am comparing distance of two geometries in different >>>>> spatial refs which I do a lot. >>>>> >>>>> I still don't like the hack even if you disregard the above or if >>>>> you must hack -- don't give it the same name as the non-hacked >>>>> > functions. > >>>>> the whole idea of picking BestSRID for a person to cater to less >>>>> technical users I find extremely annoying as I can think of 20 >>>>> "BestSRID" depending on what I am doing. If they get to that >>>>> level of sophistication, I would rather have them think a little >>>>> more and understand the implications of those decisions. >>>>> >>>>> We must learn to crawl before we can learn to walk,because walking >>>>> without understanding will just get you into trouble in the long run. >>>>> >>>>> >>>>> Thanks, >>>>> Regina >>>>> >>>>> -----Original Message----- >>>>> From: postgis-devel-bounces@... >>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>> Of Paul Ramsey >>>>> Sent: Friday, October 30, 2009 9:47 PM >>>>> To: PostGIS Development Discussion >>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>> >>>>> You *can*, but I strongly doubt you *will*. Because there's >>>>> nothing in geography that isn't already in geometry. So you as a >>>>> primary geometry user are going to have no working need to cast things >>>>> > to geography. > >>>>> On the other hand, the very first question from users of geography >>>>> will be "how can I access ?" So having a relatively full set of >>>>> functions already available in geography makes sense to me, even >>>>> if they are hacked in with a planar trick. >>>>> >>>>> P. >>>>> >>>>> On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation wrote: >>>>> >>>>>> Paul, >>>>>> I can put a functional geography index on can't I and take >>>>>> advantage of geography index bindings? >>>>>> >>>>>> Lets say I have a large network of tables broken out by region so >>>>>> I know a specific table has one srid. >>>>>> >>>>>> For many queries, I may go to that table directly or if I'm doing >>>>>> single geometry processing, really don't care what srid as long >>>>>> as its in utm or whatever - so I can use the full power of GEOS. >>>>>> >>>>>> For my across the board distance checks and so forth, I would >>>>>> want to use geography and I could use a geography index if I put >>>>>> a functional geography index on my geometry correct? Though that >>>>>> needs some more >>>>>> >>>>> testing. >>>>> >>>>>> So in short if 90% of my workload involves geometry processing, I >>>>>> will want to keep my data in geometry >>>>>> >>>>>> But the 10% I would want to convert to geography on the fly. >>>>>> >>>>>> Thanks, >>>>>> Regina >>>>>> >>>>>> -----Original Message----- >>>>>> From: postgis-devel-bounces@... >>>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>>> Of Paul Ramsey >>>>>> Sent: Friday, October 30, 2009 8:34 PM >>>>>> To: PostGIS Development Discussion >>>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>>> >>>>>> I'm not sure I understand why you would ever convert a geometry >>>>>> to a geography as part of a query on a geometry table. I fully >>>>>> expect geography to be used as a storage type, because of the >>>>>> utility of having the correct spherical indexes, which are not >>>>>> available when you're just converting in via a cast. Since >>>>>> there's no functions available on geography that are not already >>>>>> available on geometry, why would you ever do a >>>>>> geometry->geography cast unless you are (a) testing geography or >>>>>> (b) bulk converting a table into geography for >>>>>> >>>>> storage in that type. >>>>> >>>>>> P. >>>>>> >>>>>> >>>>>> >>>>>> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation wrote: >>>>>> >>>>>>> Paul, >>>>>>> I would rather you didn't for 2 reasons >>>>>>> >>>>>>> 1) I'm lazy and for each of these things we'd have to apply the >>>>>>> text additional function proto hack to prevent from it breaking >>>>>>> > geometry. > >>>>>>> which we will probably end up taking out anyway. >>>>>>> >>>>>>> 2) I don't like the hiddenness of it since it becomes especially >>>>>>> annoying if you have your native in geometry and you are >>>>>>> converting to geography for a special usecase, then you end up >>>>>>> with a slower implementation >>>>>>> >>>>>>> as you would really end up doing accidentally >>>>>>> >>>>>>> geometry -> geography -> geometry ->operation (and why do I want >>>>>>> my calcs done in UTM?) >>>>>>> >>>>>>> Instead of the more efficient >>>>>>> >>>>>>> geometry -> operation >>>>>>> >>>>>>> Thanks, >>>>>>> Regina >>>>>>> >>>>>>> -----Original Message----- >>>>>>> From: postgis-devel-bounces@... >>>>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>>>> Of Paul Ramsey >>>>>>> Sent: Friday, October 30, 2009 8:16 PM >>>>>>> To: PostGIS Development Discussion >>>>>>> Subject: [postgis-devel] Geog/Geom Hack >>>>>>> >>>>>>> I'm interested to know what the general opinion is of the trick >>>>>>> I've used on >>>>>>> ST_Buffer(geography): >>>>>>> >>>>>>> >>>>>>> >> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in. >> >>>>>>> c >>>>>>> #L541 >>>>>>> >>>>>>> I ask because I could apply the same idea to the larger suite of >>>>>>> OGC SFSQL predicates before release. Is half-a-loaf better than >>>>>>> no loaf in >>>>>>> >>>>>> this case? >>>>>> >>>>>>> (Note that there will be failure cases for really large >>>>>>> geometry, like a polygon of "Asia" or "Russia" that have >>>>>>> polygons over the >>>>>>> dateline.) >>>>>>> >>>>>>> P. >>>>>>> _______________________________________________ >>>>>>> postgis-devel mailing list >>>>>>> postgis-devel@... >>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>> >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> postgis-devel mailing list >>>>>>> postgis-devel@... >>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>> >>>>>>> >>>>>> _______________________________________________ >>>>>> postgis-devel mailing list >>>>>> postgis-devel@... >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>> >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> postgis-devel mailing list >>>>>> postgis-devel@... >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>> >>>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>> _______________________________________________ >>>> postgis-devel mailing list >>>> postgis-devel@... >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>> >>>> >>>> _______________________________________________ >>>> postgis-devel mailing list >>>> postgis-devel@... >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>> >>>> >>>> _______________________________________________ >>>> postgis-devel mailing list >>>> postgis-devel@... >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>> >>>> >>> _______________________________________________ >>> postgis-devel mailing list >>> postgis-devel@... >>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>> >>> >>> >> ---------------------------------------------------------------------- >> -- >> >> _______________________________________________ >> postgis-users mailing list >> postgis-users@... >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> > > > -- > ------------------------------ > José Carlos Martínez Llario > > Producción Cartográfica y SIG. > Dpto. Ingeniería Cartográfica. > Univ. Politécnica de Valencia. > > E-mail: jomarlla@... > Telf: 963877007 ext. 75599 > ------------------------------ > > _______________________________________________ > postgis-users mailing list > postgis-users@... > http://postgis.refractions.net/mailman/listinfo/postgis-users > > > _______________________________________________ > postgis-users mailing list > postgis-users@... > http://postgis.refractions.net/mailman/listinfo/postgis-users > -- ------------------------------ José Carlos Martínez Llario Producción Cartográfica y SIG. Dpto. Ingeniería Cartográfica. Univ. Politécnica de Valencia. E-mail: jomarlla@... Telf: 963877007 ext. 75599 ------------------------------ _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: [postgis-devel] Geog/Geom Hack
by Jose Carlos Martinez
::
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Hi all,
Talking about this topics..maybe I can help a little bit to some users that do not have clear this problem and then they can help about the topic you are talking about the functions names, etc. Lets get the intersection of two lines that use a geographic coordinate system (GCS), this case: epsg 4230 The result 1) is the normal PostGIS behavior. But the point: POINT(-1.5 40) is a wrong result from a cartographic point of view (but if we use a GCS then we are talking about cartography right?). The result 2) (we transform the GCS to a Projected reference system valid according to the study area (ED50UTM 30N -> EPSG 23030) and of course using the same ellipsoid (4230): This POINT(-1.50026115912186 40.0157573310178) has a little error but it is much better approach that 1) 3) The perfect result would be to calculate the two geodetic lines and to intersect them directly in 4230 but this is much more complicated. I think PostGIS should avoid using the first behavior (I do not think the result 1 is acceptable) and at least to transform to a correct Projected coordinate system. This task can be done automatically by checking the SRID and finding out if it corresponds to a GCS, that case just transform the data . Of course, still remain the tolerance problem that I tried to explain in the previous post. 1) sp3=# select st_asewkt(st_intersection(l0,l1)) from (select st_geomfromtext ('SRID=4230;LINESTRING (-2 39, -1 41)') as l0, st_geomfromtext ('SRID=4230;LINESTRING (-1 39, -2 41)') as l1) as foo; st_asewkt -------------------------- SRID=4230;POINT(-1.5 40) 2) sp3=# select st_asewkt(st_transform (st_intersection(l0t, l1t),4230)) from (select st_transform (l0,23030) as l0t, st_transform(l1,23030) as l1t from (select st_geomfromtext ('SRID=4230;LINESTRING (-2 39, -1 41)') as l0, st_geomfromtext ('SRID=4230;LINESTRING (-1 39, -2 41)') as l1) as foo) as foo; st_asewkt ----------------------------------------------------- SRID=4230;POINT(-1.50026115912186 40.0157573310178) (1 row) Cheers, Jose Jose Carlos Martinez Llario wrote: > Thanks a lot Regina as you said it can be so confusing for users. > I understood now the problem you guys are talking about. > > But I would like to go back again to the geodetic problem with not > trivial method (ST_Intersects..., ST_Intersection.., etc.) > I am reading the OGC 06-103r3 now..and for example OGC says in buffer: > "Becaose of the limitations of linear interpolation, there will often > be some relatively small error in this distance" > They extends too this comment in general to any geometry operation so > they are assuming that > > So I think they admit small errors (I do not how big..), anyways they > talk just about LINEAR interpolation. Maybe the OGC didnt think a lot > about geographic coordinates when they wrote this specifications or > maybe they are working in other specifications right now...no idea.. > > Anyways if PostGIS transforms the coordinates from geographic to some > projection before calling GEOS..then I think PostGIS/GEOS should > use some coordinate tolerance inside the spatial operators and > predicates, otherwise geometries that intersect, overlap, etc in the > real world (real world is the ellipsoid or at least sphere) are not > going to intersect, overlap,etc. in projected coordinates. > > Thanx, > Best, > Jose > > Paragon Corporation wrote: >> Jose, >> >> Paul can answer this better than I can. >> right now the functions we have published for geodetic (ST_Length, >> ST_Distance, AT_Area etc) do not use shortest line along a plane like >> GEOS/JTS or current PostGIS distance etc. -- they are genuinely >> measuring >> along a sphere/spheroid. >> >> So the only issue we are talking about as you said is the cases where we >> don't have a true geodetic answer for right now. >> >> Paul's approach is to find the best spatial ref for it (whatever that >> means?) -- transform it to that and then do the JTS/GEOS operations >> and to >> pass this off as a correct answer. >> >> My point is yes that's generally the right thing to do, but not >> always - it >> becomes wrong depending on how big of a thing you are talking about >> (and the >> both good and bad thing about geography is that you can be talking about >> bigger things than you can easily with a correct planar) . So while >> having >> these functions makes peoples lives easier -- it also makes them >> difficult, >> because now you can't distinguish the really good functions we have >> designed >> specifically for sphere/spheroid from these hackish estimates. No >> novice or >> advanced user would be able to do this without constantly referring >> to the >> docs. How relevant this is to know is my question? >> >> Thus came the other solution of just naming them differently that >> Nicklas >> proposed so one can tell by the name that these are doing some >> questionable >> (and possibly costly) things behind the scenes. >> >> Thanks, >> Regina >> >> >> >> -----Original Message----- >> From: postgis-users-bounces@... >> [mailto:postgis-users-bounces@...] On Behalf Of Jose >> Carlos Martinez Llario >> Sent: Saturday, October 31, 2009 12:34 PM >> To: PostGIS Users Discussion >> Subject: Re: [postgis-users] [postgis-devel] Geog/Geom Hack >> >> Hi everyone, >> Maybe I did not understand all the chat about Geographic coordinates >> but if >> you guys are planning to use geographic coordinates in PostGIS in a >> wide way >> then what is going to happen with all the spatial predicates >> (DE9IM) and the spatial operators based on GEOS/JTS? >> >> Please correct me if I am wrong but I think GEOS/JTS are based on 'the >> shortest line between 2 points is a line so they are using lineal >> interpolation' and not a geodesic line (sphere or ellipsoid) as we >> need to >> work with geographic coordinates. Theses libraries should be rewritten >> taking into account this fact, dont you think so?..In fact right now >> if you >> intersect two lines with GEOS/JTS (geographic >> coordinates) the result is wrong (even if GEOS had a sphere approach >> since >> it would keep being wrong in rigorous point of view). >> >> The approach about projecting the geographic coordinates before >> calling GEOS >> to a projection with the smallest errors and choosing the right type >> (equivalent projections, conforming projection) could be the 'only' >> approach now? >> >> Thanks, >> Jose Carlos Martinez >> >> >> >> >> Paragon Corporation wrote: >> >>> Nicklas and Paul, >>> >>> Yap that's the main point. To add >>> >>> I'm not really in disagreement with Paul. I see his point too. I'm >>> just prodding him to think about all his use cases a little more >>> because I don't feel he has. >>> >>> My feelings to sum up >>> 1) We have not thought about the complete ramifications of this hack >>> and I'm really concerned about the novice that transitions to an >>> expert rather than just getting them hooked on PostGIS. Perhaps I'm >>> being overly silly with that and even said, Paul's approach might be >>> an easier to transition solution. >>> >>> 2) My concern is the penalty of putting it in and having to take it >>> out later might be very great (both from a code, testing, as well >>> as a mindset perspective). I just feel it needs more thought and >>> testing and really if we want to make our December deadline, I don't >>> want it rushed in so lightly. >>> >>> Unless of course Paul -- you want to wait till January or February >>> to release 1.5? >>> >>> Now the ST_Max_Distance is a separate issue. I would put in the >>> ST_ConvexHull hack in place. The reason being is that it just >>> improves performance any way I can think you slice it and an >>> experienced user would do exactly the same thing always and when you >>> finally incorporate it into the core function, there is no change >>> in existing code just a speed improvement. So to me its basically >>> our ST_DWithin hack -- a very tried and trued obvious answer. Its >>> an implementation detail with no clear leaky effects. >>> >>> With that said, there are some clear functions in geometry that are >>> safe to put a geography cover over. Those ones where there is >>> clearly only one answer and don't involve transformation. >>> >>> like ST_X, ST_Y etc. That don't require transformation so no screw >>> up in data. Also observe that even the geometry(geography .... in >>> these there is no penalty becuase the geometry/geography isn't >>> changing so the planner can cache the geometry to geography >>> conversion. The ST_Transformation ones however, the >>> geometry/geography is changing slightly at each step since >>> ST_Tranformation is a lossy operation so you are not only incurring >>> overhead (because these answers can't be cached), but also adding in >>> extra errors . >>> >>> To me this is a bleeding abstraction and that is the main reason I >>> don't like it. >>> >>> So getting back to you Paul, >>> >>> What functions exactly are you planning to put a veil over? >>> ST_Buffer well that one is used so much and is not as exact anyway >>> that I suppose I can grudgingly accept that as okay. >>> >>> Thanks, >>> Regina >>> >>> >>> ---------------------------------------------------------------------- >>> -- >>> *From:* postgis-devel-bounces@... >>> [mailto:postgis-devel-bounces@...] *On Behalf Of >>> *nicklas.aven@... >>> *Sent:* Saturday, October 31, 2009 10:04 AM >>> *To:* PostGIS Development Discussion >>> *Subject:* Re: [postgis-devel] Geog/Geom Hack >>> >>> Hallo >>> >>> I can see the points from both of you. I think the most important >>> argument from you Regina is that it is not transparent enough. A >>> skillfull user trying postgis might be disapointed when realizing >>> that the nested functions caused an unnecessary big rounding-error. >>> But if it is obvious that it is a "special" function at least for >>> the experienced user knowing about common function-names I don't >>> think it is a big problem and might work as an easy shortcut at >>> least during the process of learning. >>> >>> As I understand it this could be a solution for using many functions >>> against geography so, why not note it in the function name like: >>> ST_tBuffer for transformed buffer. Then when time is to introduse a >>> "real" variant of the function they can coexist and it will not >>> change the bahavior inside an application without someone >>> consciously changes >> >> >>> the function name and remove the t. >>> >>> the t would be independent of geography-geometry in semantics and >>> just indicate that it is a lower-precision variant. I fit was >>> commonly used it would work as a warning to experienced users. >>> >>> I have a similar question about st_max_distance. The function gets >>> very much more effective when ran together with convexhull. I saw >>> the trick in ST_MinimumBoundingCircle and id makes a big difference >>> to do : >>> st_max_distance(st_convexhull(the_geom)) instead of just >>> st_max_distance(the_geom). >>> The question is: Should that be put in the sql-function? >>> My opinion now is that we just tell about it in the documentation >>> and aims at doing that trick internally in C in the future. Maybe >>> together with moving the whole convexhull to postgis-native from >>> geos. It didn't look that impossible fromthe JTS-code. >>> >>> /Nicklas >>> >>> >>> 2009-10-31 Paul Ramsey wrote: >>> >>> I still think I'm right :) Honestly, I've got to a lot of trouble to >>> >>>> make this stuff for newbies, and I don't think "learn how it works" >>>> is the right answer for them. They had that option before, but >>>> taking GIS >>>> 101 is not an option for these people, they need something that >>>> "just works". It's easier to teach the experienced people the >>>> pitfalls than the inexperienced people the basics. >>>> >>>> BTW, I just upgraded distance_sphere and distance_spheroid to be as >>>> powerful (handling point/line/polygon) as the geography variants, >>>> removing excuses for transforming geometries into geographies for >>>> processing purposes. >>>> >>>> P. >>>> >>>> On Fri, Oct 30, 2009 at 9:15 PM, Paragon Corporation wrote: >>>> >>>>> Paul, >>>>> For what its worth, here is another reason why I don't like this >>>>> >>> idea and I >>> >>>>> think we should at least think about its ramifications more so >>>>> >>> should put it >>> >>>>> off for consideration until 2.0. >>>>> >>>>> In geometry processing, its common practice to apply a lot of >>>>> >>> functions in >>> >>>>> succession >>>>> >>>>> process1(process2(process3(geometry/geography) >>>>> >>>>> With your hackish approach -- the unsuspecting novice user will be >>>>> >>> incurring >>> >>>>> a lot of transformation rounding errors with each process >>>>> >>>>> The advanced user, won't know if this is okay or not -- because >>>>> >>> they can't >>> >>>>> tell by looking at the function call the hidden transformations >>>>> >>> going on. >>> >>>>> If these did not exist, they would transform once before the >>>>> >>> processes and >>> >>>>> once after) and incurr much less penalty >>>>> >>>>> But if they both exist, they will treat them as being on equal >>>>> footing >>>>> >>>>> ST_Buffer(geometry) and ST_Buffer(geography) >>>>> >>>>> >>>>> So your approach while well-meaning gives a questionable benefit to >>>>> >>> novices >>> >>>>> and is putting experienced users at a disadvantage. >>>>> >>>>> Thanks, >>>>> Regina >>>>> >>>>> -----Original Message----- >>>>> From: postgis-devel-bounces@... >>>>> [mailto:postgis-devel-bounces@...] On Behalf Of >>>>> >>> Paragon >>> >>>>> Corporation >>>>> Sent: Friday, October 30, 2009 11:54 PM >>>>> To: 'PostGIS Development Discussion' >>>>> Cc: 'PostGIS Users Discussion' >>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>> >>>>> Paul, >>>>> I suppose we can't just put this decision off till 2.0. Isn't this >>>>> >>> a bit of >>> >>>>> scope creep? I'm not absolutely sure which way is better, but I >>>>> >>> know the >>> >>>>> cost of rolling back the change is more. >>>>> >>>>> If you are going to do this, how many functions are you planning to >>>>> >>> do this >>> >>>>> for? >>>>> >>>>> I'm cc'ing the postgis users group too to get more of an opinion on >>>>> >>> this >>> >>>>> topic. >>>>> >>>>> So the question is it it a good idea to introduce a hack that >>>>> >>> transforms a >>> >>>>> geography into what we call BestSRID to perform geometry operations >>>>> >>> on and >>> >>>>> then transform back. My concern is that this is a silent operation >>>>> >>> that >>> >>>>> gives the impression that these functions are natively done in >>>>> spheroid space just for the benefit of catering to less technical >>>>> >> users. >> >>>>> >>> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.c >>> #L541 >>> >>>>> So you can't really tell by looking the penalty >>>>> >>>>> Main examples of this as shown for ST_Buffer >>>>> >>>>> CREATE OR REPLACE FUNCTION _ST_BestSRID(geography, geography) >>>>> 530 RETURNS integer >>>>> 531 AS 'MODULE_PATHNAME','geography_bestsrid' >>>>> 532 LANGUAGE 'C' IMMUTABLE STRICT; >>>>> 533 >>>>> 534 -- Availability: 1.5.0 >>>>> 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) >>>>> 536 RETURNS integer >>>>> 537 AS 'SELECT _ST_BestSRID($1,$1)' >>>>> 538 LANGUAGE 'SQL' IMMUTABLE STRICT; >>>>> 539 >>>>> 540 -- Availability: 1.5.0 >>>>> 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) >>>>> 542 RETURNS geography >>>>> 543 AS 'SELECT >>>>> geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), >>>>> _ST_BestSRID($1)), $2), 4326))' >>>>> 544 LANGUAGE 'SQL' IMMUTABLE STRICT; >>>>> 545 >>>>> >>>>> >>>>> >>>>> Thanks, >>>>> Regina >>>>> >>>>> -----Original Message----- >>>>> From: postgis-devel-bounces@... >>>>> [mailto:postgis-devel-bounces@...] On Behalf Of >>>>> >>> Paul >>> >>>>> Ramsey >>>>> Sent: Friday, October 30, 2009 11:07 PM >>>>> To: PostGIS Development Discussion >>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>> >>>>> We're going to have to agree to disagree on this one, Regina. >>> Catering to >>> >>>>> the less technical users is what this exercise is all about, to my >>>>> >>> mind, and >>> >>>>> that includes allowing easy flipping into geometry for calculations >>>>> >>> that >>> >>>>> aren't supported in geography yet. Oracle does this too. >>>>> >>>>> What do other folks think? >>>>> >>>>> P. >>>>> >>>>> On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation wrote: >>>>> >>>>>> Paul, >>>>>> Hmm when I am comparing distance of two geometries in different >>>>>> spatial refs which I do a lot. >>>>>> >>>>>> I still don't like the hack even if you disregard the above or if >>>>>> you must hack -- don't give it the same name as the non-hacked >>>>>> >> functions. >> >>>>>> the whole idea of picking BestSRID for a person to cater to less >>>>>> technical users I find extremely annoying as I can think of 20 >>>>>> "BestSRID" depending on what I am doing. If they get to that >>>>>> level of sophistication, I would rather have them think a little >>>>>> more and understand the implications of those decisions. >>>>>> >>>>>> We must learn to crawl before we can learn to walk,because >>>>>> walking without understanding will just get you into trouble in >>>>>> the long run. >>>>>> >>>>>> >>>>>> Thanks, >>>>>> Regina >>>>>> >>>>>> -----Original Message----- >>>>>> From: postgis-devel-bounces@... >>>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>>> Of Paul Ramsey >>>>>> Sent: Friday, October 30, 2009 9:47 PM >>>>>> To: PostGIS Development Discussion >>>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>>> >>>>>> You *can*, but I strongly doubt you *will*. Because there's >>>>>> nothing in geography that isn't already in geometry. So you as a >>>>>> primary geometry user are going to have no working need to cast >>>>>> things >>>>>> >> to geography. >> >>>>>> On the other hand, the very first question from users of >>>>>> geography will be "how can I access ?" So having a relatively >>>>>> full set of functions already available in geography makes sense >>>>>> to me, even if they are hacked in with a planar trick. >>>>>> >>>>>> P. >>>>>> >>>>>> On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation wrote: >>>>>> >>>>>>> Paul, >>>>>>> I can put a functional geography index on can't I and take >>>>>>> advantage of geography index bindings? >>>>>>> >>>>>>> Lets say I have a large network of tables broken out by region >>>>>>> so I know a specific table has one srid. >>>>>>> >>>>>>> For many queries, I may go to that table directly or if I'm >>>>>>> doing single geometry processing, really don't care what srid as >>>>>>> long as its in utm or whatever - so I can use the full power of >>>>>>> GEOS. >>>>>>> >>>>>>> For my across the board distance checks and so forth, I would >>>>>>> want to use geography and I could use a geography index if I put >>>>>>> a functional geography index on my geometry correct? Though >>>>>>> that needs some more >>>>>>> >>>>>> testing. >>>>>> >>>>>>> So in short if 90% of my workload involves geometry processing, >>>>>>> I will want to keep my data in geometry >>>>>>> >>>>>>> But the 10% I would want to convert to geography on the fly. >>>>>>> >>>>>>> Thanks, >>>>>>> Regina >>>>>>> >>>>>>> -----Original Message----- >>>>>>> From: postgis-devel-bounces@... >>>>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>>>> Of Paul Ramsey >>>>>>> Sent: Friday, October 30, 2009 8:34 PM >>>>>>> To: PostGIS Development Discussion >>>>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>>>> >>>>>>> I'm not sure I understand why you would ever convert a geometry >>>>>>> to a geography as part of a query on a geometry table. I fully >>>>>>> expect geography to be used as a storage type, because of the >>>>>>> utility of having the correct spherical indexes, which are not >>>>>>> available when you're just converting in via a cast. Since >>>>>>> there's no functions available on geography that are not already >>>>>>> available on geometry, why would you ever do a >>>>>>> geometry->geography cast unless you are (a) testing geography or >>>>>>> (b) bulk converting a table into geography for >>>>>>> >>>>>> storage in that type. >>>>>> >>>>>>> P. >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation wrote: >>>>>>> >>>>>>>> Paul, >>>>>>>> I would rather you didn't for 2 reasons >>>>>>>> >>>>>>>> 1) I'm lazy and for each of these things we'd have to apply the >>>>>>>> text additional function proto hack to prevent from it breaking >>>>>>>> >> geometry. >> >>>>>>>> which we will probably end up taking out anyway. >>>>>>>> >>>>>>>> 2) I don't like the hiddenness of it since it becomes >>>>>>>> especially annoying if you have your native in geometry and you >>>>>>>> are converting to geography for a special usecase, then you end >>>>>>>> up with a slower implementation >>>>>>>> >>>>>>>> as you would really end up doing accidentally >>>>>>>> >>>>>>>> geometry -> geography -> geometry ->operation (and why do I >>>>>>>> want my calcs done in UTM?) >>>>>>>> >>>>>>>> Instead of the more efficient >>>>>>>> >>>>>>>> geometry -> operation >>>>>>>> >>>>>>>> Thanks, >>>>>>>> Regina >>>>>>>> >>>>>>>> -----Original Message----- >>>>>>>> From: postgis-devel-bounces@... >>>>>>>> [mailto:postgis-devel-bounces@...] On >>>>>>>> Behalf Of Paul Ramsey >>>>>>>> Sent: Friday, October 30, 2009 8:16 PM >>>>>>>> To: PostGIS Development Discussion >>>>>>>> Subject: [postgis-devel] Geog/Geom Hack >>>>>>>> >>>>>>>> I'm interested to know what the general opinion is of the trick >>>>>>>> I've used on >>>>>>>> ST_Buffer(geography): >>>>>>>> >>>>>>>> >>>>>>>> >>> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in. >>> >>>>>>>> c >>>>>>>> #L541 >>>>>>>> >>>>>>>> I ask because I could apply the same idea to the larger suite >>>>>>>> of OGC SFSQL predicates before release. Is half-a-loaf better >>>>>>>> than no loaf in >>>>>>>> >>>>>>> this case? >>>>>>> >>>>>>>> (Note that there will be failure cases for really large >>>>>>>> geometry, like a polygon of "Asia" or "Russia" that have >>>>>>>> polygons over the >>>>>>>> dateline.) >>>>>>>> >>>>>>>> P. >>>>>>>> _______________________________________________ >>>>>>>> postgis-devel mailing list >>>>>>>> postgis-devel@... >>>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> postgis-devel mailing list >>>>>>>> postgis-devel@... >>>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>>> >>>>>>>> >>>>>>> _______________________________________________ >>>>>>> postgis-devel mailing list >>>>>>> postgis-devel@... >>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>> >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> postgis-devel mailing list >>>>>>> postgis-devel@... >>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>> >>>>>>> >>>>>> _______________________________________________ >>>>>> postgis-devel mailing list >>>>>> postgis-devel@... >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> postgis-devel mailing list >>>>>> postgis-devel@... >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>> >>>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>> _______________________________________________ >>>> postgis-devel mailing list >>>> postgis-devel@... >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>> >>>> >>>> >>> ---------------------------------------------------------------------- >>> -- >>> >>> _______________________________________________ >>> postgis-users mailing list >>> postgis-users@... >>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> >> >> >> -- >> ------------------------------ >> José Carlos Martínez Llario >> >> Producción Cartográfica y SIG. >> Dpto. Ingeniería Cartográfica. >> Univ. Politécnica de Valencia. >> >> E-mail: jomarlla@... >> Telf: 963877007 ext. 75599 >> ------------------------------ >> >> _______________________________________________ >> postgis-users mailing list >> postgis-users@... >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> >> _______________________________________________ >> postgis-users mailing list >> postgis-users@... >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> > > -- ------------------------------ José Carlos Martínez Llario Producción Cartográfica y SIG. Dpto. Ingeniería Cartográfica. Univ. Politécnica de Valencia. E-mail: jomarlla@... Telf: 963877007 ext. 75599 ------------------------------ _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: [postgis-devel] Geog/Geom Hack
by Paragon Corporation-2
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Jose,
For what its worth, I think the ST_Dwithin for geography takes care of the ST_Intersects case nicely. And that for example to me would be a no brainer overload for ST_Intersects. It will be slower than the geometry ST_Intersects, but would give the right answer. The ST_Intersection example also brings up the point of what if the projected srid you calculate to be the best for each geometry is different? Or I suppose you would take both into consideration and figure out based on area or something. Though that would still not be quite right. I'm thinking these things have to be analyzed on a per function basis (rather than a sweeping answer of Yes lets overload everything people commonly use). So Paul -- what functions exactly did you have in mind? Thanks, Regina -----Original Message----- From: postgis-users-bounces@... [mailto:postgis-users-bounces@...] On Behalf Of Jose Carlos Martinez Llario Sent: Saturday, October 31, 2009 2:17 PM To: PostGIS Users Discussion Subject: Re: [postgis-users] [postgis-devel] Geog/Geom Hack Hi all, Talking about this topics..maybe I can help a little bit to some users that do not have clear this problem and then they can help about the topic you are talking about the functions names, etc. Lets get the intersection of two lines that use a geographic coordinate system (GCS), this case: epsg 4230 The result 1) is the normal PostGIS behavior. But the point: POINT(-1.5 40) is a wrong result from a cartographic point of view (but if we use a GCS then we are talking about cartography right?). The result 2) (we transform the GCS to a Projected reference system valid according to the study area (ED50UTM 30N -> EPSG 23030) and of course using the same ellipsoid (4230): This POINT(-1.50026115912186 40.0157573310178) has a little error but it is much better approach that 1) 3) The perfect result would be to calculate the two geodetic lines and to intersect them directly in 4230 but this is much more complicated. I think PostGIS should avoid using the first behavior (I do not think the result 1 is acceptable) and at least to transform to a correct Projected coordinate system. This task can be done automatically by checking the SRID and finding out if it corresponds to a GCS, that case just transform the data . Of course, still remain the tolerance problem that I tried to explain in the previous post. 1) sp3=# select st_asewkt(st_intersection(l0,l1)) from (select st_geomfromtext ('SRID=4230;LINESTRING (-2 39, -1 41)') as l0, st_geomfromtext ('SRID=4230;LINESTRING (-1 39, -2 41)') as l1) as foo; st_asewkt -------------------------- SRID=4230;POINT(-1.5 40) 2) sp3=# select st_asewkt(st_transform (st_intersection(l0t, l1t),4230)) from (select st_transform (l0,23030) as l0t, st_transform(l1,23030) as l1t from (select st_geomfromtext ('SRID=4230;LINESTRING (-2 39, -1 41)') as l0, st_geomfromtext ('SRID=4230;LINESTRING (-1 39, -2 41)') as l1) as foo) as foo; st_asewkt ----------------------------------------------------- SRID=4230;POINT(-1.50026115912186 40.0157573310178) (1 row) Cheers, Jose Jose Carlos Martinez Llario wrote: > Thanks a lot Regina as you said it can be so confusing for users. > I understood now the problem you guys are talking about. > > But I would like to go back again to the geodetic problem with not > trivial method (ST_Intersects..., ST_Intersection.., etc.) I am > reading the OGC 06-103r3 now..and for example OGC says in buffer: > "Becaose of the limitations of linear interpolation, there will often > be some relatively small error in this distance" > They extends too this comment in general to any geometry operation so > they are assuming that > > So I think they admit small errors (I do not how big..), anyways they > talk just about LINEAR interpolation. Maybe the OGC didnt think a lot > about geographic coordinates when they wrote this specifications or > maybe they are working in other specifications right now...no idea.. > > Anyways if PostGIS transforms the coordinates from geographic to some > projection before calling GEOS..then I think PostGIS/GEOS should use > some coordinate tolerance inside the spatial operators and predicates, > otherwise geometries that intersect, overlap, etc in the real world > (real world is the ellipsoid or at least sphere) are not going to > intersect, overlap,etc. in projected coordinates. > > Thanx, > Best, > Jose > > Paragon Corporation wrote: >> Jose, >> >> Paul can answer this better than I can. >> right now the functions we have published for geodetic (ST_Length, >> ST_Distance, AT_Area etc) do not use shortest line along a plane like >> GEOS/JTS or current PostGIS distance etc. -- they are genuinely >> measuring along a sphere/spheroid. >> >> So the only issue we are talking about as you said is the cases where >> we don't have a true geodetic answer for right now. >> >> Paul's approach is to find the best spatial ref for it (whatever that >> means?) -- transform it to that and then do the JTS/GEOS operations >> and to pass this off as a correct answer. >> >> My point is yes that's generally the right thing to do, but not >> always - it becomes wrong depending on how big of a thing you are >> talking about (and the both good and bad thing about geography is >> that you can be talking about bigger things than you can easily with >> a correct planar) . So while having these functions makes peoples >> lives easier -- it also makes them difficult, because now you can't >> distinguish the really good functions we have designed specifically >> for sphere/spheroid from these hackish estimates. No novice or >> advanced user would be able to do this without constantly referring >> to the docs. How relevant this is to know is my question? >> >> Thus came the other solution of just naming them differently that >> Nicklas proposed so one can tell by the name that these are doing >> some questionable (and possibly costly) things behind the scenes. >> >> Thanks, >> Regina >> >> >> >> -----Original Message----- >> From: postgis-users-bounces@... >> [mailto:postgis-users-bounces@...] On Behalf Of >> Jose Carlos Martinez Llario >> Sent: Saturday, October 31, 2009 12:34 PM >> To: PostGIS Users Discussion >> Subject: Re: [postgis-users] [postgis-devel] Geog/Geom Hack >> >> Hi everyone, >> Maybe I did not understand all the chat about Geographic coordinates >> but if you guys are planning to use geographic coordinates in PostGIS >> in a wide way then what is going to happen with all the spatial >> predicates >> (DE9IM) and the spatial operators based on GEOS/JTS? >> >> Please correct me if I am wrong but I think GEOS/JTS are based on >> 'the shortest line between 2 points is a line so they are using >> lineal interpolation' and not a geodesic line (sphere or ellipsoid) >> as we need to work with geographic coordinates. Theses libraries >> should be rewritten taking into account this fact, dont you think >> so?..In fact right now if you intersect two lines with GEOS/JTS >> (geographic >> coordinates) the result is wrong (even if GEOS had a sphere approach >> since it would keep being wrong in rigorous point of view). >> >> The approach about projecting the geographic coordinates before >> calling GEOS to a projection with the smallest errors and choosing >> the right type (equivalent projections, conforming projection) could >> be the 'only' >> approach now? >> >> Thanks, >> Jose Carlos Martinez >> >> >> >> >> Paragon Corporation wrote: >> >>> Nicklas and Paul, >>> >>> Yap that's the main point. To add >>> >>> I'm not really in disagreement with Paul. I see his point too. I'm >>> just prodding him to think about all his use cases a little more >>> because I don't feel he has. >>> >>> My feelings to sum up >>> 1) We have not thought about the complete ramifications of this hack >>> and I'm really concerned about the novice that transitions to an >>> expert rather than just getting them hooked on PostGIS. Perhaps I'm >>> being overly silly with that and even said, Paul's approach might be >>> an easier to transition solution. >>> >>> 2) My concern is the penalty of putting it in and having to take it >>> out later might be very great (both from a code, testing, as well >>> as a mindset perspective). I just feel it needs more thought and >>> testing and really if we want to make our December deadline, I don't >>> want it rushed in so lightly. >>> >>> Unless of course Paul -- you want to wait till January or February >>> to release 1.5? >>> >>> Now the ST_Max_Distance is a separate issue. I would put in the >>> ST_ConvexHull hack in place. The reason being is that it just >>> improves performance any way I can think you slice it and an >>> experienced user would do exactly the same thing always and when you >>> finally incorporate it into the core function, there is no change >>> in existing code just a speed improvement. So to me its basically >>> our ST_DWithin hack -- a very tried and trued obvious answer. Its >>> an implementation detail with no clear leaky effects. >>> >>> With that said, there are some clear functions in geometry that are >>> safe to put a geography cover over. Those ones where there is >>> clearly only one answer and don't involve transformation. >>> >>> like ST_X, ST_Y etc. That don't require transformation so no screw >>> up in data. Also observe that even the geometry(geography .... in >>> these there is no penalty becuase the geometry/geography isn't >>> changing so the planner can cache the geometry to geography >>> conversion. The ST_Transformation ones however, the >>> geometry/geography is changing slightly at each step since >>> ST_Tranformation is a lossy operation so you are not only incurring >>> overhead (because these answers can't be cached), but also adding in >>> extra errors . >>> >>> To me this is a bleeding abstraction and that is the main reason I >>> don't like it. >>> >>> So getting back to you Paul, >>> >>> What functions exactly are you planning to put a veil over? >>> ST_Buffer well that one is used so much and is not as exact anyway >>> that I suppose I can grudgingly accept that as okay. >>> >>> Thanks, >>> Regina >>> >>> >>> -------------------------------------------------------------------- >>> -- >>> -- >>> *From:* postgis-devel-bounces@... >>> [mailto:postgis-devel-bounces@...] *On Behalf Of >>> *nicklas.aven@... >>> *Sent:* Saturday, October 31, 2009 10:04 AM >>> *To:* PostGIS Development Discussion >>> *Subject:* Re: [postgis-devel] Geog/Geom Hack >>> >>> Hallo >>> >>> I can see the points from both of you. I think the most important >>> argument from you Regina is that it is not transparent enough. A >>> skillfull user trying postgis might be disapointed when realizing >>> that the nested functions caused an unnecessary big rounding-error. >>> But if it is obvious that it is a "special" function at least for >>> the experienced user knowing about common function-names I don't >>> think it is a big problem and might work as an easy shortcut at >>> least during the process of learning. >>> >>> As I understand it this could be a solution for using many functions >>> against geography so, why not note it in the function name like: >>> ST_tBuffer for transformed buffer. Then when time is to introduse a >>> "real" variant of the function they can coexist and it will not >>> change the bahavior inside an application without someone >>> consciously changes >> >> >>> the function name and remove the t. >>> >>> the t would be independent of geography-geometry in semantics and >>> just indicate that it is a lower-precision variant. I fit was >>> commonly used it would work as a warning to experienced users. >>> >>> I have a similar question about st_max_distance. The function gets >>> very much more effective when ran together with convexhull. I saw >>> the trick in ST_MinimumBoundingCircle and id makes a big difference >>> to do : >>> st_max_distance(st_convexhull(the_geom)) instead of just >>> st_max_distance(the_geom). >>> The question is: Should that be put in the sql-function? >>> My opinion now is that we just tell about it in the documentation >>> and aims at doing that trick internally in C in the future. Maybe >>> together with moving the whole convexhull to postgis-native from >>> geos. It didn't look that impossible fromthe JTS-code. >>> >>> /Nicklas >>> >>> >>> 2009-10-31 Paul Ramsey wrote: >>> >>> I still think I'm right :) Honestly, I've got to a lot of trouble to >>> >>>> make this stuff for newbies, and I don't think "learn how it works" >>>> is the right answer for them. They had that option before, but >>>> taking GIS >>>> 101 is not an option for these people, they need something that >>>> "just works". It's easier to teach the experienced people the >>>> pitfalls than the inexperienced people the basics. >>>> >>>> BTW, I just upgraded distance_sphere and distance_spheroid to be as >>>> powerful (handling point/line/polygon) as the geography variants, >>>> removing excuses for transforming geometries into geographies for >>>> processing purposes. >>>> >>>> P. >>>> >>>> On Fri, Oct 30, 2009 at 9:15 PM, Paragon Corporation wrote: >>>> >>>>> Paul, >>>>> For what its worth, here is another reason why I don't like this >>>>> >>> idea and I >>> >>>>> think we should at least think about its ramifications more so >>>>> >>> should put it >>> >>>>> off for consideration until 2.0. >>>>> >>>>> In geometry processing, its common practice to apply a lot of >>>>> >>> functions in >>> >>>>> succession >>>>> >>>>> process1(process2(process3(geometry/geography) >>>>> >>>>> With your hackish approach -- the unsuspecting novice user will be >>>>> >>> incurring >>> >>>>> a lot of transformation rounding errors with each process >>>>> >>>>> The advanced user, won't know if this is okay or not -- because >>>>> >>> they can't >>> >>>>> tell by looking at the function call the hidden transformations >>>>> >>> going on. >>> >>>>> If these did not exist, they would transform once before the >>>>> >>> processes and >>> >>>>> once after) and incurr much less penalty >>>>> >>>>> But if they both exist, they will treat them as being on equal >>>>> footing >>>>> >>>>> ST_Buffer(geometry) and ST_Buffer(geography) >>>>> >>>>> >>>>> So your approach while well-meaning gives a questionable benefit >>>>> to >>>>> >>> novices >>> >>>>> and is putting experienced users at a disadvantage. >>>>> >>>>> Thanks, >>>>> Regina >>>>> >>>>> -----Original Message----- >>>>> From: postgis-devel-bounces@... >>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>> Of >>>>> >>> Paragon >>> >>>>> Corporation >>>>> Sent: Friday, October 30, 2009 11:54 PM >>>>> To: 'PostGIS Development Discussion' >>>>> Cc: 'PostGIS Users Discussion' >>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>> >>>>> Paul, >>>>> I suppose we can't just put this decision off till 2.0. Isn't >>>>> this >>>>> >>> a bit of >>> >>>>> scope creep? I'm not absolutely sure which way is better, but I >>>>> >>> know the >>> >>>>> cost of rolling back the change is more. >>>>> >>>>> If you are going to do this, how many functions are you planning >>>>> to >>>>> >>> do this >>> >>>>> for? >>>>> >>>>> I'm cc'ing the postgis users group too to get more of an opinion >>>>> on >>>>> >>> this >>> >>>>> topic. >>>>> >>>>> So the question is it it a good idea to introduce a hack that >>>>> >>> transforms a >>> >>>>> geography into what we call BestSRID to perform geometry >>>>> operations >>>>> >>> on and >>> >>>>> then transform back. My concern is that this is a silent >>>>> operation >>>>> >>> that >>> >>>>> gives the impression that these functions are natively done in >>>>> spheroid space just for the benefit of catering to less technical >>>>> >> users. >> >>>>> >>> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in >>> .c >>> #L541 >>> >>>>> So you can't really tell by looking the penalty >>>>> >>>>> Main examples of this as shown for ST_Buffer >>>>> >>>>> CREATE OR REPLACE FUNCTION _ST_BestSRID(geography, geography) >>>>> 530 RETURNS integer >>>>> 531 AS 'MODULE_PATHNAME','geography_bestsrid' >>>>> 532 LANGUAGE 'C' IMMUTABLE STRICT; >>>>> 533 >>>>> 534 -- Availability: 1.5.0 >>>>> 535 CREATE OR REPLACE FUNCTION _ST_BestSRID(geography) >>>>> 536 RETURNS integer >>>>> 537 AS 'SELECT _ST_BestSRID($1,$1)' >>>>> 538 LANGUAGE 'SQL' IMMUTABLE STRICT; >>>>> 539 >>>>> 540 -- Availability: 1.5.0 >>>>> 541 CREATE OR REPLACE FUNCTION ST_Buffer(geography, float8) >>>>> 542 RETURNS geography >>>>> 543 AS 'SELECT >>>>> geography(ST_Transform(ST_Buffer(ST_Transform(geometry($1), >>>>> _ST_BestSRID($1)), $2), 4326))' >>>>> 544 LANGUAGE 'SQL' IMMUTABLE STRICT; >>>>> 545 >>>>> >>>>> >>>>> >>>>> Thanks, >>>>> Regina >>>>> >>>>> -----Original Message----- >>>>> From: postgis-devel-bounces@... >>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>> Of >>>>> >>> Paul >>> >>>>> Ramsey >>>>> Sent: Friday, October 30, 2009 11:07 PM >>>>> To: PostGIS Development Discussion >>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>> >>>>> We're going to have to agree to disagree on this one, Regina. >>> Catering to >>> >>>>> the less technical users is what this exercise is all about, to my >>>>> >>> mind, and >>> >>>>> that includes allowing easy flipping into geometry for >>>>> calculations >>>>> >>> that >>> >>>>> aren't supported in geography yet. Oracle does this too. >>>>> >>>>> What do other folks think? >>>>> >>>>> P. >>>>> >>>>> On Fri, Oct 30, 2009 at 7:06 PM, Paragon Corporation wrote: >>>>> >>>>>> Paul, >>>>>> Hmm when I am comparing distance of two geometries in different >>>>>> spatial refs which I do a lot. >>>>>> >>>>>> I still don't like the hack even if you disregard the above or if >>>>>> you must hack -- don't give it the same name as the non-hacked >>>>>> >> functions. >> >>>>>> the whole idea of picking BestSRID for a person to cater to less >>>>>> technical users I find extremely annoying as I can think of 20 >>>>>> "BestSRID" depending on what I am doing. If they get to that >>>>>> level of sophistication, I would rather have them think a little >>>>>> more and understand the implications of those decisions. >>>>>> >>>>>> We must learn to crawl before we can learn to walk,because >>>>>> walking without understanding will just get you into trouble in >>>>>> the long run. >>>>>> >>>>>> >>>>>> Thanks, >>>>>> Regina >>>>>> >>>>>> -----Original Message----- >>>>>> From: postgis-devel-bounces@... >>>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>>> Of Paul Ramsey >>>>>> Sent: Friday, October 30, 2009 9:47 PM >>>>>> To: PostGIS Development Discussion >>>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>>> >>>>>> You *can*, but I strongly doubt you *will*. Because there's >>>>>> nothing in geography that isn't already in geometry. So you as a >>>>>> primary geometry user are going to have no working need to cast >>>>>> things >>>>>> >> to geography. >> >>>>>> On the other hand, the very first question from users of >>>>>> geography will be "how can I access ?" So having a relatively >>>>>> full set of functions already available in geography makes sense >>>>>> to me, even if they are hacked in with a planar trick. >>>>>> >>>>>> P. >>>>>> >>>>>> On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation wrote: >>>>>> >>>>>>> Paul, >>>>>>> I can put a functional geography index on can't I and take >>>>>>> advantage of geography index bindings? >>>>>>> >>>>>>> Lets say I have a large network of tables broken out by region >>>>>>> so I know a specific table has one srid. >>>>>>> >>>>>>> For many queries, I may go to that table directly or if I'm >>>>>>> doing single geometry processing, really don't care what srid as >>>>>>> long as its in utm or whatever - so I can use the full power of >>>>>>> GEOS. >>>>>>> >>>>>>> For my across the board distance checks and so forth, I would >>>>>>> want to use geography and I could use a geography index if I put >>>>>>> a functional geography index on my geometry correct? Though >>>>>>> that needs some more >>>>>>> >>>>>> testing. >>>>>> >>>>>>> So in short if 90% of my workload involves geometry processing, >>>>>>> I will want to keep my data in geometry >>>>>>> >>>>>>> But the 10% I would want to convert to geography on the fly. >>>>>>> >>>>>>> Thanks, >>>>>>> Regina >>>>>>> >>>>>>> -----Original Message----- >>>>>>> From: postgis-devel-bounces@... >>>>>>> [mailto:postgis-devel-bounces@...] On Behalf >>>>>>> Of Paul Ramsey >>>>>>> Sent: Friday, October 30, 2009 8:34 PM >>>>>>> To: PostGIS Development Discussion >>>>>>> Subject: Re: [postgis-devel] Geog/Geom Hack >>>>>>> >>>>>>> I'm not sure I understand why you would ever convert a geometry >>>>>>> to a geography as part of a query on a geometry table. I fully >>>>>>> expect geography to be used as a storage type, because of the >>>>>>> utility of having the correct spherical indexes, which are not >>>>>>> available when you're just converting in via a cast. Since >>>>>>> there's no functions available on geography that are not already >>>>>>> available on geometry, why would you ever do a >>>>>>> geometry->geography cast unless you are (a) testing geography or >>>>>>> (b) bulk converting a table into geography for >>>>>>> >>>>>> storage in that type. >>>>>> >>>>>>> P. >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation wrote: >>>>>>> >>>>>>>> Paul, >>>>>>>> I would rather you didn't for 2 reasons >>>>>>>> >>>>>>>> 1) I'm lazy and for each of these things we'd have to apply the >>>>>>>> text additional function proto hack to prevent from it breaking >>>>>>>> >> geometry. >> >>>>>>>> which we will probably end up taking out anyway. >>>>>>>> >>>>>>>> 2) I don't like the hiddenness of it since it becomes >>>>>>>> especially annoying if you have your native in geometry and you >>>>>>>> are converting to geography for a special usecase, then you end >>>>>>>> up with a slower implementation >>>>>>>> >>>>>>>> as you would really end up doing accidentally >>>>>>>> >>>>>>>> geometry -> geography -> geometry ->operation (and why do I >>>>>>>> want my calcs done in UTM?) >>>>>>>> >>>>>>>> Instead of the more efficient >>>>>>>> >>>>>>>> geometry -> operation >>>>>>>> >>>>>>>> Thanks, >>>>>>>> Regina >>>>>>>> >>>>>>>> -----Original Message----- >>>>>>>> From: postgis-devel-bounces@... >>>>>>>> [mailto:postgis-devel-bounces@...] On >>>>>>>> Behalf Of Paul Ramsey >>>>>>>> Sent: Friday, October 30, 2009 8:16 PM >>>>>>>> To: PostGIS Development Discussion >>>>>>>> Subject: [postgis-devel] Geog/Geom Hack >>>>>>>> >>>>>>>> I'm interested to know what the general opinion is of the trick >>>>>>>> I've used on >>>>>>>> ST_Buffer(geography): >>>>>>>> >>>>>>>> >>>>>>>> >>> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in. >>> >>>>>>>> c >>>>>>>> #L541 >>>>>>>> >>>>>>>> I ask because I could apply the same idea to the larger suite >>>>>>>> of OGC SFSQL predicates before release. Is half-a-loaf better >>>>>>>> than no loaf in >>>>>>>> >>>>>>> this case? >>>>>>> >>>>>>>> (Note that there will be failure cases for really large >>>>>>>> geometry, like a polygon of "Asia" or "Russia" that have >>>>>>>> polygons over the >>>>>>>> dateline.) >>>>>>>> >>>>>>>> P. >>>>>>>> _______________________________________________ >>>>>>>> postgis-devel mailing list >>>>>>>> postgis-devel@... >>>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> postgis-devel mailing list >>>>>>>> postgis-devel@... >>>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>>> >>>>>>>> >>>>>>> _______________________________________________ >>>>>>> postgis-devel mailing list >>>>>>> postgis-devel@... >>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>> >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> postgis-devel mailing list >>>>>>> postgis-devel@... >>>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>>> >>>>>>> >>>>>> _______________________________________________ >>>>>> postgis-devel mailing list >>>>>> postgis-devel@... >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> postgis-devel mailing list >>>>>> postgis-devel@... >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>>> >>>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>>> _______________________________________________ >>>>> postgis-devel mailing list >>>>> postgis-devel@... >>>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>>> >>>>> >>>> _______________________________________________ >>>> postgis-devel mailing list >>>> postgis-devel@... >>>> http://postgis.refractions.net/mailman/listinfo/postgis-devel >>>> >>>> >>>> >>> -------------------------------------------------------------------- >>> -- >>> -- >>> >>> _______________________________________________ >>> postgis-users mailing list >>> postgis-users@... >>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> >> >> >> -- >> ------------------------------ >> José Carlos Martínez Llario >> >> Producción Cartográfica y SIG. >> Dpto. Ingeniería Cartográfica. >> Univ. Politécnica de Valencia. >> >> E-mail: jomarlla@... >> Telf: 963877007 ext. 75599 >> ------------------------------ >> >> _______________________________________________ >> postgis-users mailing list >> postgis-users@... >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> >> _______________________________________________ >> postgis-users mailing list >> postgis-users@... >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> > > -- ------------------------------ José Carlos Martínez Llario Producción Cartográfica y SIG. Dpto. Ingeniería Cartográfica. Univ. Politécnica de Valencia. E-mail: jomarlla@... Telf: 963877007 ext. 75599 ------------------------------ _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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