Nabble - PostGIS - User

Re: Small benchmark with PostGIS and MS SQL-ServerSpatial: Any suggestions?

2009-11-09T19:52:33Z

Right. You probably won't be able to actually publish the numbers as
Stanley pointed out, but for your own knowledge, I agree with Paul -
round out your testing with
different spatial joins, like STContains, STTouches, STCrosses, etc.
with different geometry types (point/point, point/line, point/poly,
line/line, line/poly, poly/poly). Test with different geometry sizes.

Test the spatial index by performing queries like "SELECT count(*) FROM
mytable WHERE geom.Filter(@geom)" (the && equivalent operator in
PostGIS) over large tables, each of a different geometry type.

Personally, I would limit the number of tests like you have in #4.
Although interesting, you won't know how STArea and STIntersects
comparatively perform using such a query (since they're both in the same
query). Rather, test raw computation speed by computing the buffer,
area, centroid, boundary, isvalid, pointonsurface, etc (in different
tests of course) of several large polygonal tables (one with small
polygons, one with large polygons, one mixed, etc).

Try STUnion-ing an entire table of polygons and again of lines. If you
really want to send shivers up your spine, I highly recommend you throw
in some simple point-in-polygon tests (ie. 100's of thousands of points
in a single large polygon of several 10's of thousands of vertices). I
know Lion King is an old show, but I can't help but think "Mufasa".

Cheers,
Kevin

Sufficool, Stanley wrote:

> Read the EULA on MSSQL first.
>
> 5. BENCHMARK TESTING. You must obtain Microsoft's prior written approval to disclose to a third party the results of any benchmark test of the software. However, this does not apply to the Microsoft .NET Framework (see below).
>
>
>
>> -----Original Message-----
>> From: postgis-users-bounces@...
>> [mailto:postgis-users-bounces@...] On
>> Behalf Of Paul Ramsey
>> Sent: Monday, November 09, 2009 3:08 PM
>> To: PostGIS Users Discussion
>> Subject: Re: [postgis-users] Small benchmark with PostGIS and
>> MS SQL-ServerSpatial: Any suggestions?
>>
>>
>> On Mon, Nov 9, 2009 at 11:55 AM, Stefan Keller
>> <sfkeller@...> wrote:
>>
>>
>>> 1. Loading data (SELECT * INTO...) and generating indices (CREATE
>>> SPATIAL INDEX...)
>>>
>>> 2. Non-spatial selection query (inc. filling table):
>>> SELECT * INTO query2_result FROM {dataset} t
>>> WHERE t.Name = n;
>>>
>> Don't do "SELECT INTO" as you'll muddy your query performance
>> with insert performance.
>>
>>
>>> 3. Spatial query (inc. filling table):
>>> SELECT * FROM {dataset} t INTO query3_result
>>> WHERE t.geom.STIntersects(@poly) = 1
>>>
>> I try to do these kinds of queries with a "SELECT count(*)"
>> so that there is no penalty converting the rows returned into
>> some kind of output format.
>>
>>
>>> 4. Combining two spatial functions (inc. filling table):
>>> SELECT * FROM {polygons} t INTO query3_result
>>> WHERE STArea(t.geom)>x AND t.geom.STIntersects(@poly) = 1
>>>
>>> 5. Join of a linestring and a point table (inc. filling table):
>>> SELECT s.* FROM {linestrings} t
>>> INNER JOIN {points} s ON STDistance(t.geom, s.geom) <= x INTO
>>> query5_result
>>> WHERE t.Type = 'Autobahn'
>>>
>> For PostGIS, you have to use ST_DWithin() to get an
>> equivalent query to the STDistance query above.
>>
>> Try some full table joins
>>
>> select sum(length(p.geom)) from polys p join lines l on
>> st_contains(p.geom, l.geom) where l.type = 'Autobahn'
>>
>> Mix up the typologies, do st_contains/st_intersects of
>> poly/poly, poly/line, poly/poing Mix up the geometry sizes,
>> do the above on polygon tables of counties and of tracts
>>
>> Publish all the SQL and the data tables so people can
>> critique your work before you start publishing numbers.
>>
>> P.
>> _______________________________________________
>> postgis-users mailing list postgis-users@...
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>
> _______________________________________________
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> postgis-users@...
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>

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Re: Small benchmark with PostGIS and MS SQL-ServerSpatial: Any suggestions?

2009-11-09T15:31:51Z

Read the EULA on MSSQL first.

5. BENCHMARK TESTING. You must obtain Microsoft's prior written approval to disclose to a third party the results of any benchmark test of the software. However, this does not apply to the Microsoft .NET Framework (see below).

> -----Original Message-----
> From: postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] On
> Behalf Of Paul Ramsey
> Sent: Monday, November 09, 2009 3:08 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Small benchmark with PostGIS and
> MS SQL-ServerSpatial: Any suggestions?
>
>
> On Mon, Nov 9, 2009 at 11:55 AM, Stefan Keller
> <sfkeller@...> wrote:
>
> > 1. Loading data (SELECT * INTO...) and generating indices (CREATE
> > SPATIAL INDEX...)
> >
> > 2. Non-spatial selection query (inc. filling table):
> > SELECT * INTO query2_result FROM {dataset} t
> > WHERE t.Name = n;
>
> Don't do "SELECT INTO" as you'll muddy your query performance
> with insert performance.
>
> > 3. Spatial query (inc. filling table):
> > SELECT * FROM {dataset} t INTO query3_result
> > WHERE t.geom.STIntersects(@poly) = 1
>
> I try to do these kinds of queries with a "SELECT count(*)"
> so that there is no penalty converting the rows returned into
> some kind of output format.
>
> > 4. Combining two spatial functions (inc. filling table):
> > SELECT * FROM {polygons} t INTO query3_result
> > WHERE STArea(t.geom)>x AND t.geom.STIntersects(@poly) = 1
> >
> > 5. Join of a linestring and a point table (inc. filling table):
> > SELECT s.* FROM {linestrings} t
> > INNER JOIN {points} s ON STDistance(t.geom, s.geom) <= x INTO
> > query5_result
> > WHERE t.Type = 'Autobahn'
>
> For PostGIS, you have to use ST_DWithin() to get an
> equivalent query to the STDistance query above.
>
> Try some full table joins
>
> select sum(length(p.geom)) from polys p join lines l on
> st_contains(p.geom, l.geom) where l.type = 'Autobahn'
>
> Mix up the typologies, do st_contains/st_intersects of
> poly/poly, poly/line, poly/poing Mix up the geometry sizes,
> do the above on polygon tables of counties and of tracts
>
> Publish all the SQL and the data tables so people can
> critique your work before you start publishing numbers.
>
> P.
> _______________________________________________
> postgis-users mailing list postgis-users@...
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>

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Re: Small benchmark with PostGIS and MS SQL-Server Spatial: Any suggestions?

2009-11-09T15:07:33Z

On Mon, Nov 9, 2009 at 11:55 AM, Stefan Keller <sfkeller@...> wrote:

> 1. Loading data (SELECT * INTO...) and generating indices (CREATE
> SPATIAL INDEX...)
>
> 2. Non-spatial selection query (inc. filling table):
> SELECT * INTO query2_result FROM {dataset} t
> WHERE t.Name = n;

Don't do "SELECT INTO" as you'll muddy your query performance with
insert performance.

> 3. Spatial query (inc. filling table):
> SELECT * FROM {dataset} t INTO query3_result
> WHERE t.geom.STIntersects(@poly) = 1

I try to do these kinds of queries with a "SELECT count(*)" so that
there is no penalty converting the rows returned into some kind of
output format.

> 4. Combining two spatial functions (inc. filling table):
> SELECT * FROM {polygons} t INTO query3_result
> WHERE STArea(t.geom)>x AND t.geom.STIntersects(@poly) = 1
>
> 5. Join of a linestring and a point table (inc. filling table):
> SELECT s.* FROM {linestrings} t
> INNER JOIN {points} s ON STDistance(t.geom, s.geom) <= x INTO query5_result
> WHERE t.Type = ‘Autobahn’

For PostGIS, you have to use ST_DWithin() to get an equivalent query
to the STDistance query above.

Try some full table joins

select sum(length(p.geom)) from polys p join lines l on
st_contains(p.geom, l.geom) where l.type = 'Autobahn'

Mix up the typologies, do st_contains/st_intersects of poly/poly,
poly/line, poly/poing
Mix up the geometry sizes, do the above on polygon tables of counties
and of tracts

Publish all the SQL and the data tables so people can critique your
work before you start publishing numbers.

P.
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Small benchmark with PostGIS and MS SQL-Server Spatial: Any suggestions?

2009-11-09T11:55:32Z

We're doing a small performance benchmark with PostGIS and Microsoft
SQL-Server Spatial.

We took the Tiger data from FOSS4G's "WMS Performance: Mapserver vs.
Geoserver" and are doing queries like shown below.

Any comments about these and/or suggestions about additional queries?

- Stefan

PostgreSQL syntax with curly brackets as table placeholders:

1. Loading data (SELECT * INTO...) and generating indices (CREATE
SPATIAL INDEX...)

2. Non-spatial selection query (inc. filling table):
SELECT * INTO query2_result FROM {dataset} t
WHERE t.Name = n;

3. Spatial query (inc. filling table):
SELECT * FROM {dataset} t INTO query3_result
WHERE t.geom.STIntersects(@poly) = 1

4. Combining two spatial functions (inc. filling table):
SELECT * FROM {polygons} t INTO query3_result
WHERE STArea(t.geom)>x AND t.geom.STIntersects(@poly) = 1

5. Join of a linestring and a point table (inc. filling table):
SELECT s.* FROM {linestrings} t
INNER JOIN {points} s ON STDistance(t.geom, s.geom) <= x INTO query5_result
WHERE t.Type = ‘Autobahn’
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Re: OpenStreetMap to GPS

2009-11-08T12:52:57Z

Thanks alot :) the last part of the tutorial to load the 900913.sql really wasn't useful then :) using the -l attributed helped the import to run successfully! thanks guys

On Sat, Nov 7, 2009 at 11:28 PM, Emilie Laffray <emilie.laffray@...> wrote:

Matthew Pulis wrote:
> Guys,
>
> I want to plot a list of GPS acquired locations with data originating
> from OpenStreetMap. I am thinking to keep everything in GPS projection
> since quite near in the future the project is going to be accepting
> live GPS readings.
>
> OSM SRID = 900913
>
> Should I consider GPS SRID to be: 4326?

It looks like you used osm2pgsql in its default mode. If you want to
have data in 4326 with osm2pgsql, you have to use the flag -l.
The default SRID for OSM is 4326. It is only osm2pgsql that is
transforming this into 900913 for the rendering.

Emilie Laffray

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--
Matthew Pulis
URL : http://www.matthewpulis.info | http://www.solutions-lab.net
MSN : pulis_matthew[@]hotmail.com
ICQ : 145951110
Skype : solutions-lab.net

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Re: Is that possible a function to behave differently inside and outside another main function code?

2009-11-08T09:26:41Z

Hi Kevin,

Thanks for your repply. I can't be sure whether the two functions have the same X value, and I don't want them twice, that's why I was using UNION, instead of UNION ALL (which is much faster even...).

But what you said make some sense. Do you think if use first a UNION ALL and then in the outer query (when I order by q.t) I use DISTINCT may work?

I think I will try it out.

Thanks again for the help.

Rodrigo Sperb

Kevin Neufeld wrote:

Are you sure you want to use "UNION" and not "UNION ALL"? The former
will remove duplicates, the latter does not. It's conceivable that when
UNIONed, the three SELECT st_X clauses will return a single value.
Collected and put through ST_LineFromMultiPoint would probably result in
a single point line (depending on which version of PostGIS you are using
- the newer versions will ERROR with "geometry requires more points").

Hope that helps,
Kevin

rodrigosperb wrote:
> Hello,
>
> I have a bit of a problem that is sort of driving me crazy. I need to
> perform an "addition of two (mathematical) functions". I represent them as
> linestrings in my solution, and it is part of another bigger function. The
> code is as follows:
>
> ...header...
> SELECT st_LineFromMultiPoint(st_Collect(st_MakePoint(xy.t,xy.at)))
> FROM (SELECT q.t, dr_delay_value($1,q.t) +
> dr_delay_value($3,dr_delay_value($1,q.t)) AS at
> FROM (SELECT st_X(st_PointN($1,n)) AS t
> FROM generate_series(1,st_NumPoints($1)) AS h(n)
> UNION
> SELECT st_X(st_PointN($2,n)) AS t
> FROM generate_series(1,st_NumPoints($2)) AS h(n)
> UNION
> SELECT st_Xmax($1) AS t
> ) AS q ORDER BY q.t) AS xy
> ...bottom...
> dr_delay_value() is simply a look-up function that takes the Y value for a
> certain X.
>
> The thing is that eventually this fuction is failing on returning more
> specifically a 2-points linestring (that sould) and returns only a single
> point one. Now, I have prepared a "wrapper" PL/Pgsql function to keep track
> of what is passed to that function (perhaps that was the reason for the
> error. With that I'm pretty much sure that the arguments passed are fine,
> and still get the same error... Strangely, with my wrapper function keeping
> track of the arguments passed to the function I was able to try out to run
> the same request (that inside of the bigger function fails) separately, and
> guess what? is simply works!!
>
> I hope anyone may have a clue of what is going on. That's a very strange
> behavior, I would say.
>
> Regards,
>
> Rodrigo Sperb
>
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Re: Is that possible a function to behave differently inside and outside another main function code?

2009-11-08T09:22:19Z

Are you sure you want to use "UNION" and not "UNION ALL"? The former
will remove duplicates, the latter does not. It's conceivable that when
UNIONed, the three SELECT st_X clauses will return a single value.
Collected and put through ST_LineFromMultiPoint would probably result in
a single point line (depending on which version of PostGIS you are using
- the newer versions will ERROR with "geometry requires more points").

Hope that helps,
Kevin

rodrigosperb wrote:

> Hello,
>
> I have a bit of a problem that is sort of driving me crazy. I need to
> perform an "addition of two (mathematical) functions". I represent them as
> linestrings in my solution, and it is part of another bigger function. The
> code is as follows:
>
> ...header...
> SELECT st_LineFromMultiPoint(st_Collect(st_MakePoint(xy.t,xy.at)))
> FROM (SELECT q.t, dr_delay_value($1,q.t) +
> dr_delay_value($3,dr_delay_value($1,q.t)) AS at
> FROM (SELECT st_X(st_PointN($1,n)) AS t
> FROM generate_series(1,st_NumPoints($1)) AS h(n)
> UNION
> SELECT st_X(st_PointN($2,n)) AS t
> FROM generate_series(1,st_NumPoints($2)) AS h(n)
> UNION
> SELECT st_Xmax($1) AS t
> ) AS q ORDER BY q.t) AS xy
> ...bottom...
> dr_delay_value() is simply a look-up function that takes the Y value for a
> certain X.
>
> The thing is that eventually this fuction is failing on returning more
> specifically a 2-points linestring (that sould) and returns only a single
> point one. Now, I have prepared a "wrapper" PL/Pgsql function to keep track
> of what is passed to that function (perhaps that was the reason for the
> error. With that I'm pretty much sure that the arguments passed are fine,
> and still get the same error... Strangely, with my wrapper function keeping
> track of the arguments passed to the function I was able to try out to run
> the same request (that inside of the bigger function fails) separately, and
> guess what? is simply works!!
>
> I hope anyone may have a clue of what is going on. That's a very strange
> behavior, I would say.
>
> Regards,
>
> Rodrigo Sperb
>

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Re: Postgis for dummies

2009-11-08T07:11:54Z

On Fri, Nov 6, 2009 at 7:03 PM, Fernando Tong <nandorov@...> wrote:

> I have a dummy question:
> i have a POLYGON, how can i get all the polygon's coordinates with a SELECT
> query?
> something like:
> select unknown_functions(polygon) from mytable
> output:
> 1 POINT(1 2)
> 2 POINT(2 2)
> 3 POINT(3 2)
> ...
> or much better if i get
> X Y
> 1 1 2
> 2 2 2
> 3 3 2
> Thanks a lot.
>

Maybe a

SELECT ST_AsText(polygon_column) FROM Table

Is enough

Output:

POLYGON( (1 1, 2 2, 3 3) )

> On Fri, Nov 6, 2009 at 9:19 AM, David Fawcett <david.fawcett@...>
> wrote:
>>
>> I think that another good way to approach it is to have a task/problem
>> that you want to solve using PostGIS (whether real or made up). Learn
>> what you need to about PostGIS to solve that problem and branch out
>> from there.
>>
>> David.
>>
>> On Fri, Nov 6, 2009 at 12:04 AM, Paragon Corporation <lr@...> wrote:
>> > You can also look at some of these - might be helpful
>> >
>> > http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01
>> >
>> > http://workshops.opengeo.org/stack-intro/
>> >
>> > This one is a bit dated but probably still useful
>> > http://2007.foss4g.org/workshops/W-04/
>> >
>> > Leo
>> > ________________________________
>> > From: postgis-users-bounces@...
>> > [mailto:postgis-users-bounces@...] On Behalf Of Bob
>> > and
>> > Deb
>> > Sent: Thursday, November 05, 2009 11:51 PM
>> > To: PostGIS Users Discussion
>> > Subject: Re: [postgis-users] Postgis for dummies
>> >
>> > How about the book, "PostGIS in Action" ? There is even a free chapter
>> > that might give you enough info to get started. There is also the Wiki.
>> >
>> > -Bob
>> >
>> > On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...>
>> > wrote:
>> >>
>> >> Need link to tutorial at the “dummy” level.
>> >>
>> >>
>> >>
>> >> I know a bit about kml, but that’s it. In looking at postgis, I now
>> >> see,
>> >> in the instructions, things like, “To spatially-enable a jump-oriented
>> >> static sql line pointer,….” That’s just wayyyy over me. Where do I
>> >> go as
>> >> I newbie in gis to become a pro like you all?
>> >>
>> >>
>> >>
>> >> Thanks.
>> >>
>> >> _______________________________________________
>> >> 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
>
>
> _______________________________________________
> postgis-users mailing list
> postgis-users@...
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
>

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Is that possible a function to behave differently inside and outside another main function code?

2009-11-07T23:43:32Z

Hello,

I have a bit of a problem that is sort of driving me crazy. I need to perform an "addition of two (mathematical) functions". I represent them as linestrings in my solution, and it is part of another bigger function. The code is as follows:

...header...
SELECT st_LineFromMultiPoint(st_Collect(st_MakePoint(xy.t,xy.at)))
FROM (SELECT q.t, dr_delay_value($1,q.t) + dr_delay_value($3,dr_delay_value($1,q.t)) AS at
FROM (SELECT st_X(st_PointN($1,n)) AS t
FROM generate_series(1,st_NumPoints($1)) AS h(n)
UNION
SELECT st_X(st_PointN($2,n)) AS t
FROM generate_series(1,st_NumPoints($2)) AS h(n)
UNION
SELECT st_Xmax($1) AS t
) AS q ORDER BY q.t) AS xy
...bottom...
dr_delay_value() is simply a look-up function that takes the Y value for a certain X.

The thing is that eventually this fuction is failing on returning more specifically a 2-points linestring (that sould) and returns only a single point one. Now, I have prepared a "wrapper" PL/Pgsql function to keep track of what is passed to that function (perhaps that was the reason for the error. With that I'm pretty much sure that the arguments passed are fine, and still get the same error... Strangely, with my wrapper function keeping track of the arguments passed to the function I was able to try out to run the same request (that inside of the bigger function fails) separately, and guess what? is simply works!!

I hope anyone may have a clue of what is going on. That's a very strange behavior, I would say.

Regards,

Rodrigo Sperb

Re: Postgis for dummies

2009-11-07T18:34:37Z

There's another workshop available at
http://revenant.ca/www/postgis/workshop/

--
Mark

Paragon Corporation wrote:

>
> You can also look at some of these - might be helpful
>
> http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01
>
> http://workshops.opengeo.org/stack-intro/
>
> This one is a bit dated but probably still useful
> http://2007.foss4g.org/workshops/W-04/
>
> Leo
>
> *From:* postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] *On Behalf Of
> *Bob and Deb
> *Sent:* Thursday, November 05, 2009 11:51 PM
> *To:* PostGIS Users Discussion
> *Subject:* Re: [postgis-users] Postgis for dummies
>
> How about the book, "PostGIS in Action <http://www.manning.com/obe/>"
> ? There is even a free chapter that might give you enough info to get
> started. There is also the Wiki
> <http://trac.osgeo.org/postgis/wiki/UsersWikiMain>.
>
> -Bob
>
> On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...
> <mailto:info@...>> wrote:
>
> Need link to tutorial at the “dummy” level.
>
>
>
> I know a bit about kml, but that’s it. In looking at postgis, I now
> see, in the instructions, things like, “To spatially-enable a
> jump-oriented static sql line pointer,….” That’s just wayyyy over
> me. Where do I go as I newbie in gis to become a pro like you all?
>
>
>
> Thanks.
>
>
> _______________________________________________
> postgis-users mailing list
> postgis-users@...
> <mailto: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: OpenStreetMap to GPS

2009-11-07T14:28:37Z

Matthew Pulis wrote:

> Guys,
>
> I want to plot a list of GPS acquired locations with data originating
> from OpenStreetMap. I am thinking to keep everything in GPS projection
> since quite near in the future the project is going to be accepting
> live GPS readings.
>
> OSM SRID = 900913
>
> Should I consider GPS SRID to be: 4326?

It looks like you used osm2pgsql in its default mode. If you want to

have data in 4326 with osm2pgsql, you have to use the flag -l.
The default SRID for OSM is 4326. It is only osm2pgsql that is
transforming this into 900913 for the rendering.

Emilie Laffray

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Re: OpenStreetMap to GPS

2009-11-07T13:37:33Z

Matthew Pulis <mpulis@...> writes:

> I want to plot a list of GPS acquired locations with data originating from
> OpenStreetMap. I am thinking to keep everything in GPS projection since
> quite near in the future the project is going to be accepting live GPS
> readings.
>
> OSM SRID = 900913
>
> Should I consider GPS SRID to be: 4326?
>
> However when I try to transform this geometry:
>
> gis=# select astext(way), asewkt(way), st_srid(way) from malta_roads
> gis-# where osm_id = 23561453;

Have you looked at the .osm file with an editor to see what's actually
in it?

I think you'll find that the data in the osm file is actually in SRID
4326. Certainly the osm file saved by JOSM is in this format, and also
e.g. the Massachusetts state extract of the planet file from cloudmade.

It is true that OSM uses google spherical mercator for creating map
tiles, but those are then projected coordinates rather than what appears
in the vector database. It is of course possible that your vector file
has been pre-transformed to something unusual, but from my experience
with osm that would be somewhat odd.

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attachment0 (200 bytes) Download Attachment

OpenStreetMap to GPS

2009-11-07T12:59:14Z

Guys,

I want to plot a list of GPS acquired locations with data originating from OpenStreetMap. I am thinking to keep everything in GPS projection since quite near in the future the project is going to be accepting live GPS readings.

OSM SRID = 900913

Should I consider GPS SRID to be: 4326?

However when I try to transform this geometry:

gis=# select astext(way), asewkt(way), st_srid(way) from malta_roads
gis-# where osm_id = 23561453;
astext | asewkt | st_srid
------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+---------
LINESTRING(1582821.69 4304893.15,1582810.45 4304860.01,1582804.55 4304849.75,1582790.4 4304824.81,1582776.19 4304794.61,1582748.85 4304746.72) | SRID=900913;LINESTRING(1582821.69 4304893.15,1582810.45 4304860.01,1582804.55 4304849.75,1582790.4 4304824.81,1582776.19 4304794.61,1582748.85 4304746.72) | 900913
(1 row)

I get:

gis=# select astext(st_transform(way, 4326)) from malta_roads
gis-# where osm_id = 23561453;
ERROR: transform: couldn't project point (1.58281e+06 4.30486e+06 0): failed to load NAD27-83 correction file (-38)
HINT: PostGIS was unable to transform the point because either no grid shift files were found, or the point does not lie within the range for which the grid shift is defined. Refer to the ST_Transform() section of the PostGIS manual for details on how to configure PostGIS to alter this behaviour.
gis=#

The data in malta_roads has been acquired from OpenSreetMap in a file .osm. Data regards Maltese roads.

Thanks for your help and Happy Weekend!

--
Matthew Pulis
URL : http://www.matthewpulis.info | http://www.solutions-lab.net
MSN : pulis_matthew[@]hotmail.com
ICQ : 145951110
Skype : solutions-lab.net

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Re: Postgis for dummies

2009-11-06T21:04:10Z

The best way? Unfortunately, at this point in time, I'm afraid so.
We've had this on our wish list for some time now
(http://trac.osgeo.org/postgis/ticket/76). If you want, you can import
a plpgsql implementation of this until it's implemented in C
(http://trac.osgeo.org/postgis/attachment/ticket/76/my_st_dump_points.2.sql).

Usage would be something like:
SELECT ST_AsText( (ST_DumpPoints( poly )).geom )
FROM (
SELECT 'POLYGON((0 0, 1 1, 1 0, 0 0))'::geometry AS poly
) AS foo;

st_astext
------------
POINT(0 0)
POINT(1 1)
POINT(1 0)
POINT(0 0)
(4 rows)

Cheers,
Kevin

Fernando Tong wrote:

> it works, thank you very much. However, i wonder if this is the best
> way (:
>
> On Fri, Nov 6, 2009 at 1:26 PM, Moen, Paul T. <pmoen@...
> <mailto:pmoen@...>> wrote:
>
>
> SELECT DISTINCT ST_X(ST_POINTN(foo.lines,foo.index)) AS
> x,ST_Y(ST_POINTN(foo.lines,foo.index)) AS y FROM
> (select thelines.lines,generate_series(1,thelines.n) AS index FROM
> (select polys.geo AS lines, ST_NUMPOINTS(polys.geo) AS n FROM
> (SELECT ST_BOUNDARY((ST_DUMP(the_geom)).geom) AS geo FROM
> "YOURTABLE" WHERE YOURQUERY) AS polys)
> AS thelines)
> AS foo;
>
>
> should work for multipolygons and polygons.although there may be
> an easier way.
>
>
> Paul Moen
>
>
> On Nov 6, 2009, at 12:03 PM, Fernando Tong wrote:
>
>> I have a dummy question:
>>
>> i have a POLYGON, how can i get all the polygon's coordinates
>> with a SELECT query?
>>
>> something like:
>> select unknown_functions(polygon) from mytable
>>
>> output:
>> 1 POINT(1 2)
>> 2 POINT(2 2)
>> 3 POINT(3 2)
>> ...
>>
>> or much better if i get
>> X Y
>> 1 1 2
>> 2 2 2
>> 3 3 2
>>
>> Thanks a lot.
>>
>>
>> On Fri, Nov 6, 2009 at 9:19 AM, David Fawcett
>> <david.fawcett@... <mailto:david.fawcett@...>> wrote:
>>
>> I think that another good way to approach it is to have a
>> task/problem
>> that you want to solve using PostGIS (whether real or made
>> up). Learn
>> what you need to about PostGIS to solve that problem and
>> branch out
>> from there.
>>
>> David.
>>
>> On Fri, Nov 6, 2009 at 12:04 AM, Paragon Corporation
>> <lr@... <mailto:lr@...>> wrote:
>> > You can also look at some of these - might be helpful
>> >
>> >
>> http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01
>> >
>> > http://workshops.opengeo.org/stack-intro/
>> >
>> > This one is a bit dated but probably still useful
>> > http://2007.foss4g.org/workshops/W-04/
>> >
>> > Leo
>> > ________________________________
>> > From: postgis-users-bounces@...
>> <mailto:postgis-users-bounces@...>
>> > [mailto:postgis-users-bounces@...
>> <mailto:postgis-users-bounces@...>] On
>> Behalf Of Bob and
>> > Deb
>> > Sent: Thursday, November 05, 2009 11:51 PM
>> > To: PostGIS Users Discussion
>> > Subject: Re: [postgis-users] Postgis for dummies
>> >
>> > How about the book, "PostGIS in Action" ? There is even a
>> free chapter
>> > that might give you enough info to get started. There is
>> also the Wiki.
>> >
>> > -Bob
>> >
>> > On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews
>> <info@... <mailto:info@...>>
>> > wrote:
>> >>
>> >> Need link to tutorial at the “dummy” level.
>> >>
>> >>
>> >>
>> >> I know a bit about kml, but that’s it. In looking at
>> postgis, I now see,
>> >> in the instructions, things like, “To spatially-enable a
>> jump-oriented
>> >> static sql line pointer,….” That’s just wayyyy over me.
>> Where do I go as
>> >> I newbie in gis to become a pro like you all?
>> >>
>> >>
>> >>
>> >> Thanks.
>> >>
>> >> _______________________________________________
>> >> postgis-users mailing list
>> >> postgis-users@...
>> <mailto:postgis-users@...>
>> >> http://postgis.refractions.net/mailman/listinfo/postgis-users
>> >>
>> >
>> >
>> > _______________________________________________
>> > postgis-users mailing list
>> > postgis-users@...
>> <mailto:postgis-users@...>
>> > http://postgis.refractions.net/mailman/listinfo/postgis-users
>> >
>> >
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users@...
>> <mailto:postgis-users@...>
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users@...
>> <mailto:postgis-users@...>
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
>
> _______________________________________________
> postgis-users mailing list
> postgis-users@...
> <mailto: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: Using plpgsql for in select with st_dump

2009-11-06T20:22:10Z

You have a typo in both of your "output := ..." lines. You've declared
tmpgeo, not tempgeo.
Also, you're missing a line to increment count. Perhaps after the inner
if statement, "count := count+1;"
Hope that helps,
Kevin

Moen, Paul T. wrote:

> I am trying to expand my horizons and learn some plpgsq. I want to
> split out a list of points from a multipoint via plpgsql into json,
> not geojson. I get the following notices.
>
> ERROR: missing FROM-clause entry for table "tempgeo"
> LINE 1: SELECT $1 ||'{"x":'|| $2 ||',"y":'||tempgeo.they||'}'
> ^
> QUERY: SELECT $1 ||'{"x":'|| $2 ||',"y":'||tempgeo.they||'}'
> CONTEXT: PL/pgSQL function "pointsfromgeom" line 16 at assignment
>
> ********** Error **********
>
> ERROR: missing FROM-clause entry for table "tempgeo"
> SQL state: 42P01
> Context: PL/pgSQL function "pointsfromgeom" line 16 at assignment
>
> Is there any way to do this? Does the record type have to be based on
> an existing table? Is this the right list to ask?
>
> CREATE OR REPLACE FUNCTION pointsfromgeom(ingeom GEOMETRY) RETURNS
> TEXT AS $$
> DECLARE
> geotype TEXT;
> output TEXT:='';
> BEGIN
> SELECT INTO geotype geometrytype(ingeom);
> IF (geotype = 'MULTIPOINT') THEN
> DECLARE
> tmpgeo RECORD;
> count integer :=1;
> BEGIN
> FOR tmpgeo IN SELECT DISTINCT st_x((st_dump(ingeom)).geom) as
> thex,st_y((st_dump(ingeom)).geom) as they
> LOOP
> IF (count=1) THEN
> output := '[{"x":'||tmpgeo.thex||',"y":'||tempgeo.they||'}';
> ELSE
> output := output||',{"x":'||tmpgeo.thex||',"y":'||tempgeo.they||'}';
> END IF;
> END LOOP;
> output:=output||']';
> END;
> ELSE
> RAISE NOTICE 'Geometry type is not compatable';
> RETURN NULL;
> END IF;
> RETURN output;
> END;
> $$ LANGUAGE 'plpgsql';
>
>
> Thanks,
>
> Paul
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> postgis-users mailing list
> postgis-users@...
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>

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Re: Postgis for dummies

2009-11-06T11:16:34Z

it works, thank you very much. However, i wonder if this is the best way (:

On Fri, Nov 6, 2009 at 1:26 PM, Moen, Paul T. <pmoen@...> wrote:

SELECT DISTINCT ST_X(ST_POINTN(foo.lines,foo.index)) AS x,ST_Y(ST_POINTN(foo.lines,foo.index)) AS y FROM

(select thelines.lines,generate_series(1,thelines.n) AS index FROM
(select polys.geo AS lines, ST_NUMPOINTS(polys.geo) AS n FROM

(SELECT ST_BOUNDARY((ST_DUMP(the_geom)).geom) AS geo FROM "YOURTABLE" WHERE YOURQUERY) AS polys)
AS thelines)

AS foo;

should work for multipolygons and polygons.although there may be an easier way.

Paul Moen

On Nov 6, 2009, at 12:03 PM, Fernando Tong wrote:

I have a dummy question:

i have a POLYGON, how can i get all the polygon's coordinates with a SELECT query?

something like:
select unknown_functions(polygon) from mytable

output:
1 POINT(1 2)
2 POINT(2 2)
3 POINT(3 2)
...

or much better if i get
   X Y
1 1 2
2 2 2

3 3 2

Thanks a lot.

On Fri, Nov 6, 2009 at 9:19 AM, David Fawcett <david.fawcett@...> wrote:

I think that another good way to approach it is to have a task/problem
that you want to solve using PostGIS (whether real or made up). Learn
what you need to about PostGIS to solve that problem and branch out
from there.

David.

On Fri, Nov 6, 2009 at 12:04 AM, Paragon Corporation <lr@...> wrote:
> You can also look at some of these - might be helpful
>
> http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01
>
> http://workshops.opengeo.org/stack-intro/
>
> This one is a bit dated but probably still useful
> http://2007.foss4g.org/workshops/W-04/
>
> Leo
> ________________________________
> From: postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] On Behalf Of Bob and
> Deb
> Sent: Thursday, November 05, 2009 11:51 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Postgis for dummies
>
> How about the book, "PostGIS in Action" ?   There is even a free chapter
> that might give you enough info to get started. There is also the Wiki.
>
> -Bob
>
> On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...>
> wrote:
>>
>> Need link to tutorial at the “dummy” level.
>>
>>
>>
>> I know a bit about kml, but that’s it. In looking at postgis, I now see,
>> in the instructions, things like, “To spatially-enable a jump-oriented
>> static sql line pointer,….”   That’s just wayyyy over me. Where do I go as
>> I newbie in gis to become a pro like you all?
>>
>>
>>
>> Thanks.
>>
>> _______________________________________________
>> 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 for dummies

2009-11-06T10:26:24Z

SELECT DISTINCT ST_X(ST_POINTN(foo.lines,foo.index)) AS x,ST_Y(ST_POINTN(foo.lines,foo.index)) AS y FROM

(select thelines.lines,generate_series(1,thelines.n) AS index FROM

(select polys.geo AS lines, ST_NUMPOINTS(polys.geo) AS n FROM

(SELECT ST_BOUNDARY((ST_DUMP(the_geom)).geom) AS geo FROM "YOURTABLE" WHERE YOURQUERY) AS polys)

AS thelines)

AS foo;

should work for multipolygons and polygons.although there may be an easier way.

Paul Moen

On Nov 6, 2009, at 12:03 PM, Fernando Tong wrote:

I have a dummy question:

i have a POLYGON, how can i get all the polygon's coordinates with a SELECT query?

something like:
select unknown_functions(polygon) from mytable

output:
1 POINT(1 2)
2 POINT(2 2)
3 POINT(3 2)
...

or much better if i get
   X Y
1 1 2
2 2 2

3 3 2

Thanks a lot.

On Fri, Nov 6, 2009 at 9:19 AM, David Fawcett <david.fawcett@...> wrote:

I think that another good way to approach it is to have a task/problem
that you want to solve using PostGIS (whether real or made up). Learn
what you need to about PostGIS to solve that problem and branch out
from there.

David.

On Fri, Nov 6, 2009 at 12:04 AM, Paragon Corporation <lr@...> wrote:
> You can also look at some of these - might be helpful
>
> http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01
>
> http://workshops.opengeo.org/stack-intro/
>
> This one is a bit dated but probably still useful
> http://2007.foss4g.org/workshops/W-04/
>
> Leo
> ________________________________
> From: postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] On Behalf Of Bob and
> Deb
> Sent: Thursday, November 05, 2009 11:51 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Postgis for dummies
>
> How about the book, "PostGIS in Action" ?   There is even a free chapter
> that might give you enough info to get started. There is also the Wiki.
>
> -Bob
>
> On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...>
> wrote:
>>
>> Need link to tutorial at the “dummy” level.
>>
>>
>>
>> I know a bit about kml, but that’s it. In looking at postgis, I now see,
>> in the instructions, things like, “To spatially-enable a jump-oriented
>> static sql line pointer,….”   That’s just wayyyy over me. Where do I go as
>> I newbie in gis to become a pro like you all?
>>
>>
>>
>> Thanks.
>>
>> _______________________________________________
>> 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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http://postgis.refractions.net/mailman/listinfo/postgis-users

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Re: Postgis for dummies

2009-11-06T10:03:57Z

I have a dummy question:

i have a POLYGON, how can i get all the polygon's coordinates with a SELECT query?

something like:

select unknown_functions(polygon) from mytable

output:

1 POINT(1 2)

2 POINT(2 2)

3 POINT(3 2)

...

or much better if i get

X Y

1 1 2

2 2 2

3 3 2

Thanks a lot.

On Fri, Nov 6, 2009 at 9:19 AM, David Fawcett <david.fawcett@...> wrote:

I think that another good way to approach it is to have a task/problem
that you want to solve using PostGIS (whether real or made up). Learn
what you need to about PostGIS to solve that problem and branch out
from there.

David.

On Fri, Nov 6, 2009 at 12:04 AM, Paragon Corporation <lr@...> wrote:
> You can also look at some of these - might be helpful
>
> http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01
>
> http://workshops.opengeo.org/stack-intro/
>
> This one is a bit dated but probably still useful
> http://2007.foss4g.org/workshops/W-04/
>
> Leo
> ________________________________
> From: postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] On Behalf Of Bob and
> Deb
> Sent: Thursday, November 05, 2009 11:51 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Postgis for dummies
>
> How about the book, "PostGIS in Action" ? There is even a free chapter
> that might give you enough info to get started. There is also the Wiki.
>
> -Bob
>
> On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...>
> wrote:
>>
>> Need link to tutorial at the “dummy” level.
>>
>>
>>
>> I know a bit about kml, but that’s it. In looking at postgis, I now see,
>> in the instructions, things like, “To spatially-enable a jump-oriented
>> static sql line pointer,….” That’s just wayyyy over me. Where do I go as
>> I newbie in gis to become a pro like you all?
>>
>>
>>
>> Thanks.
>>
>> _______________________________________________
>> 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
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Using plpgsql for in select with st_dump

2009-11-06T09:50:47Z

I am trying to expand my horizons and learn some plpgsq. I want to split out a list of points from a multipoint via plpgsql into json, not geojson. I get the following notices.

ERROR: missing FROM-clause entry for table "tempgeo"

LINE 1: SELECT $1 ||'{"x":'|| $2 ||',"y":'||tempgeo.they||'}'

QUERY: SELECT $1 ||'{"x":'|| $2 ||',"y":'||tempgeo.they||'}'

CONTEXT: PL/pgSQL function "pointsfromgeom" line 16 at assignment

********** Error **********

ERROR: missing FROM-clause entry for table "tempgeo"

SQL state: 42P01

Context: PL/pgSQL function "pointsfromgeom" line 16 at assignment

Is there any way to do this? Does the record type have to be based on an existing table? Is this the right list to ask?

CREATE OR REPLACE FUNCTION pointsfromgeom(ingeom GEOMETRY) RETURNS TEXT AS $$

DECLARE

geotype TEXT;

output TEXT:='';

BEGIN

SELECT INTO geotype geometrytype(ingeom);

IF (geotype = 'MULTIPOINT') THEN

DECLARE

tmpgeo RECORD;

count integer :=1;

BEGIN

FOR tmpgeo IN SELECT DISTINCT st_x((st_dump(ingeom)).geom) as thex,st_y((st_dump(ingeom)).geom) as they

LOOP

IF (count=1) THEN

output := '[{"x":'||tmpgeo.thex||',"y":'||tempgeo.they||'}';

ELSE

output := output||',{"x":'||tmpgeo.thex||',"y":'||tempgeo.they||'}';

END IF;

END LOOP;

output:=output||']';

END;

ELSE

RAISE NOTICE 'Geometry type is not compatable';

RETURN NULL;

END IF;

RETURN output;

END;

$$ LANGUAGE 'plpgsql';

Thanks,

Paul

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Re: Postgis for dummies

2009-11-06T06:19:41Z

I think that another good way to approach it is to have a task/problem
that you want to solve using PostGIS (whether real or made up). Learn
what you need to about PostGIS to solve that problem and branch out
from there.

David.

On Fri, Nov 6, 2009 at 12:04 AM, Paragon Corporation <lr@...> wrote:

> You can also look at some of these - might be helpful
>
> http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01
>
> http://workshops.opengeo.org/stack-intro/
>
> This one is a bit dated but probably still useful
> http://2007.foss4g.org/workshops/W-04/
>
> Leo
> ________________________________
> From: postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] On Behalf Of Bob and
> Deb
> Sent: Thursday, November 05, 2009 11:51 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Postgis for dummies
>
> How about the book, "PostGIS in Action" ? There is even a free chapter
> that might give you enough info to get started. There is also the Wiki.
>
> -Bob
>
> On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...>
> wrote:
>>
>> Need link to tutorial at the “dummy” level.
>>
>>
>>
>> I know a bit about kml, but that’s it. In looking at postgis, I now see,
>> in the instructions, things like, “To spatially-enable a jump-oriented
>> static sql line pointer,….” That’s just wayyyy over me. Where do I go as
>> I newbie in gis to become a pro like you all?
>>
>>
>>
>> Thanks.
>>
>> _______________________________________________
>> 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
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Re: Postgis for dummies

2009-11-05T22:04:05Z

You can also look at some of these - might be helpful

http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01

http://workshops.opengeo.org/stack-intro/

This one is a bit dated but probably still useful

http://2007.foss4g.org/workshops/W-04/

Leo

From: postgis-users-bounces@... [mailto:postgis-users-bounces@...] On Behalf Of Bob and Deb
Sent: Thursday, November 05, 2009 11:51 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Postgis for dummies

How about the book, "PostGIS in Action" ? There is even a free chapter that might give you enough info to get started. There is also the Wiki.

-Bob

On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...> wrote:

Need link to tutorial at the “dummy” level.

I know a bit about kml, but that’s it. In looking at postgis, I now see, in the instructions, things like, “To spatially-enable a jump-oriented static sql line pointer,….” That’s just wayyyy over me. Where do I go as I newbie in gis to become a pro like you all?

Thanks.

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Re: Postgis for dummies

2009-11-05T20:51:22Z

How about the book, "PostGIS in Action" ? There is even a free chapter that might give you enough info to get started. There is also the Wiki.

-Bob

On Thu, Nov 5, 2009 at 6:34 PM, Jeff Matthews <info@...> wrote:

Need link to tutorial at the “dummy” level.

I know a bit about kml, but that’s it. In looking at postgis, I now see, in the instructions, things like, “To spatially-enable a jump-oriented static sql line pointer,….” That’s just wayyyy over me. Where do I go as I newbie in gis to become a pro like you all?

Thanks.

_______________________________________________
postgis-users mailing list
postgis-users@...
http://postgis.refractions.net/mailman/listinfo/postgis-users

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Postgis for dummies

2009-11-05T18:34:41Z

Need link to tutorial at the “dummy” level.

I know a bit about kml, but that’s it. In looking at postgis, I now see, in the instructions, things like, “To spatially-enable a jump-oriented static sql line pointer,….” That’s just wayyyy over me. Where do I go as I newbie in gis to become a pro like you all?

Thanks.

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Re: SOLVED: Combining / agglomerating / clustering numbers of adjacent polygons

2009-11-05T04:49:12Z

I don't know if I have misunderstood this, but to me it looks like what you are doing is:

create table agglom_areas as
select (st_dump(st_union(the_geom))).geom as split_geom
from grid_squares;

with cascaded union (geos 3.1 or higher) this should befast as I understand it.

But if I have missunderstood everything, just ignore it :-)

/Nicklas

2009-11-05 Derek Jones wrote:

Dear Leo
>
>Hey thanks!
>
>Since these and other steps can run for several tens of minutes or even
>hours because of the data densities, I didn't notice because I left them
>each cooking and did something else instead, but I appreciate any
>improvements here because I may well be running the same kind of query
>elsewhere also.
>
>Occam's Razor and all that ;-)
>
>Kind regards
>
>Derek.
>
>Paragon Corporation wrote:
>>
>> Derek,
>>
>> FWIW -- this is a bit faster and shorter to write than your last step. You
>> probably won't notice the difference until you start dealing with huge
>> geometry collections.
>>
>> --REVISED LAST STEP
>> create table
>> agglom_areas
>> as
>> SELECT (ST_Dump(the_geom)).geom As split_geom
>> FROM temp_f;
>>
>>
>>
>> ---YOUR LAST STEP--
>>
>> create table
>> agglom_areas
>> as
>> select
>> st_GeometryN
>> (
>> the_geom,
>> generate_series(1,st_NumGeometries(the_geom))
>> ) as split_geom
>> from
>> temp_f;
>>
>>
>> Leo
>> -----Original Message-----
>> From: postgis-users-bounces@...
>> [mailto:postgis-users-bounces@...] On Behalf Of Derek
>> Jones
>> Sent: Wednesday, November 04, 2009 10:26 PM
>> Cc: PostGIS Users Discussion
>> Subject: [postgis-users] SOLVED: Combining / agglomerating / clustering
>> numbers of adjacent polygons
>>
>> Dear all,
>>
>> I solved the problem with just a handful of lines of SQL in the end... :-P
>>
>> Kinda roundabout thinking but it worked. Here's the solution:
>>
>> grid_squares contains my reduced grid set from the complete grid overlay
>> from a previous select - it's the density table. I also previously removed
>> singletons from it with a check for any grid entries that had 0 touching
>> entities.
>>
>> # Break out the multipolygon grids into polygons
>>
>> create table
>> temp_e
>> as
>> select
>> st_GeometryN
>> (
>> the_geom,
>> generate_series(1,st_NumGeometries(the_geom))
>> ) as split_geom
>> from
>> grid_squares;
>>
>> # Break out the polygons into linestrings and agglomerate into areas #
>> Becomes one big area as a multipolygon so ...
>>
>> create table
>> temp_f
>> as
>> select
>> st_buildarea
>> (
>> st_collect
>> (
>> st_ExteriorRing(split_geom)
>> )
>> ) as the_geom
>> from
>> temp_e;
>>
>> # ... afterwards, break out into polygons again # each of which is the
>> clustered set of # polygons comprising the outer boundary agglomeration # of
>> the original grid areas.
>>
>> create table
>> agglom_areas
>> as
>> select
>> st_GeometryN
>> (
>> the_geom,
>> generate_series(1,st_NumGeometries(the_geom))
>> ) as split_geom
>> from
>> temp_f;
>>
>>
>>
>> I can probably with a little work reduce the steps but I don't have a need
>> to at this point.
>>
>> This does exactly what I wanted - hope it's useful perhaps to others in the
>> same jam. Appreciate the help given in any event.
>>
>> Now I can use the generated areas to get me some centroids and then both
>> intersect and then cluster the "other" data set I have which is 10s of 1000s
>> of points and different to this one but related to it.
>>
>> Thank you again. Always useful to bounce these kinds of things around...
>>
>> Kind regards
>>
>> Derek Jones
>> _______________________________________________
>> 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: SOLVED: Combining / agglomerating / clustering numbers of adjacent polygons

2009-11-05T04:35:24Z

Dear Leo

Hey thanks!

Since these and other steps can run for several tens of minutes or even
hours because of the data densities, I didn't notice because I left them
each cooking and did something else instead, but I appreciate any
improvements here because I may well be running the same kind of query
elsewhere also.

Occam's Razor and all that ;-)

Kind regards

Derek.

Paragon Corporation wrote:

>
> Derek,
>
> FWIW -- this is a bit faster and shorter to write than your last step. You
> probably won't notice the difference until you start dealing with huge
> geometry collections.
>
> --REVISED LAST STEP
> create table
> agglom_areas
> as
> SELECT (ST_Dump(the_geom)).geom As split_geom
> FROM temp_f;
>
>
>
> ---YOUR LAST STEP--
>
> create table
> agglom_areas
> as
> select
> st_GeometryN
> (
> the_geom,
> generate_series(1,st_NumGeometries(the_geom))
> ) as split_geom
> from
> temp_f;
>
>
> Leo
> -----Original Message-----
> From: postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] On Behalf Of Derek
> Jones
> Sent: Wednesday, November 04, 2009 10:26 PM
> Cc: PostGIS Users Discussion
> Subject: [postgis-users] SOLVED: Combining / agglomerating / clustering
> numbers of adjacent polygons
>
> Dear all,
>
> I solved the problem with just a handful of lines of SQL in the end... :-P
>
> Kinda roundabout thinking but it worked. Here's the solution:
>
> grid_squares contains my reduced grid set from the complete grid overlay
> from a previous select - it's the density table. I also previously removed
> singletons from it with a check for any grid entries that had 0 touching
> entities.
>
> # Break out the multipolygon grids into polygons
>
> create table
> temp_e
> as
> select
> st_GeometryN
> (
> the_geom,
> generate_series(1,st_NumGeometries(the_geom))
> ) as split_geom
> from
> grid_squares;
>
> # Break out the polygons into linestrings and agglomerate into areas #
> Becomes one big area as a multipolygon so ...
>
> create table
> temp_f
> as
> select
> st_buildarea
> (
> st_collect
> (
> st_ExteriorRing(split_geom)
> )
> ) as the_geom
> from
> temp_e;
>
> # ... afterwards, break out into polygons again # each of which is the
> clustered set of # polygons comprising the outer boundary agglomeration # of
> the original grid areas.
>
> create table
> agglom_areas
> as
> select
> st_GeometryN
> (
> the_geom,
> generate_series(1,st_NumGeometries(the_geom))
> ) as split_geom
> from
> temp_f;
>
>
>
> I can probably with a little work reduce the steps but I don't have a need
> to at this point.
>
> This does exactly what I wanted - hope it's useful perhaps to others in the
> same jam. Appreciate the help given in any event.
>
> Now I can use the generated areas to get me some centroids and then both
> intersect and then cluster the "other" data set I have which is 10s of 1000s
> of points and different to this one but related to it.
>
> Thank you again. Always useful to bounce these kinds of things around...
>
> Kind regards
>
> Derek Jones
> _______________________________________________
> 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

Re: query question

2009-11-05T02:55:37Z

Good call!
With the following partial statement we get promising results.

round(st_area(st_intersection(r.the_geom,s.the_geom)) / st_area(r.the_geom) * 100) as Percentage

Thanks,
Ge

--- On Thu, 11/5/09, Nicolas Ribot <nicky666@...> wrote:

> From: Nicolas Ribot <nicky666@...>
> Subject: Re: [postgis-users] query question
> To: "PostGIS Users Discussion" <postgis-users@...>
> Date: Thursday, November 5, 2009, 12:45 AM
> 2009/11/5 G. van Es <gves2000@...>:
> > Thanks Maxime,
> >
> > That worked!
> >
> > However now I see another problem.
> >
> > Some polygons are touching in a way they shouldn't.
> This is a problem of our drawing department but since there
> are a few thousand of those objects it would be nice to
> query with a certain tolerance. Say, the object should
> overlap for at least 80%.
> >
>
> Hello,
>
> You could compute the actual intersection (st_intersection)
> area and
> compare its area to the initial polygons area
>
> Nicolas
>
> > Well, that is too much rocket science for me at the
> moment.
> > If someone has any clue if this is possible please
> drop me a line.
> >
> > Thanks,
> > Ge
> >
> > --- On Wed, 11/4/09, Maxime van Noppen <maxime@...>
> wrote:
> >
> >> From: Maxime van Noppen <maxime@...>
> >> Subject: Re: [postgis-users] query question
> >> To: "PostGIS Users Discussion" <postgis-users@...>
> >> Date: Wednesday, November 4, 2009, 3:56 AM
> >> G. van Es wrote:
> >> > I want to have a list of wich geometry of a
> certain
> >> type is touching or crossing another type.
> >> >
> >> > Can someone point me in the right direction?
> >>
> >> Hi,
> >>
> >> If I understand your problem you want to find for
> each
> >> geometry in your
> >> table which geometries intersect with it ?
> >>
> >> This can be done with the ST_Intersects function
> and an
> >> self-join.
> >> Something like :
> >>
> >> SELECT t1.type, t2.type FROM T t1, T t2 WHERE
> t1.type !=
> >> t2.type AND
> >> ST_Intersects(t1.the_geom, t2.the_geom);
> >>
> >> This will generate an output like :
> >>
> >> t1.type | t2.type
> >> -----------------
> >> 13 | 12
> >> 13 | 1
> >> 13 | 4
> >> 12 | 3
> >> 12 | 8
> >> ...
> >>
> >> --
> >> Maxime
> >> _______________________________________________
> >> 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
>

_______________________________________________
postgis-users mailing list
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Re: query question

2009-11-05T00:45:29Z

2009/11/5 G. van Es <gves2000@...>:
> Thanks Maxime,
>
> That worked!
>
> However now I see another problem.
>
> Some polygons are touching in a way they shouldn't. This is a problem of our drawing department but since there are a few thousand of those objects it would be nice to query with a certain tolerance. Say, the object should overlap for at least 80%.
>

Hello,

You could compute the actual intersection (st_intersection) area and
compare its area to the initial polygons area

Nicolas

> Well, that is too much rocket science for me at the moment.
> If someone has any clue if this is possible please drop me a line.
>
> Thanks,
> Ge
>
> --- On Wed, 11/4/09, Maxime van Noppen <maxime@...> wrote:
>
>> From: Maxime van Noppen <maxime@...>
>> Subject: Re: [postgis-users] query question
>> To: "PostGIS Users Discussion" <postgis-users@...>
>> Date: Wednesday, November 4, 2009, 3:56 AM
>> G. van Es wrote:
>> > I want to have a list of wich geometry of a certain
>> type is touching or crossing another type.
>> >
>> > Can someone point me in the right direction?
>>
>> Hi,
>>
>> If I understand your problem you want to find for each
>> geometry in your
>> table which geometries intersect with it ?
>>
>> This can be done with the ST_Intersects function and an
>> self-join.
>> Something like :
>>
>> SELECT t1.type, t2.type FROM T t1, T t2 WHERE t1.type !=
>> t2.type AND
>> ST_Intersects(t1.the_geom, t2.the_geom);
>>
>> This will generate an output like :
>>
>> t1.type | t2.type
>> -----------------
>> 13 | 12
>> 13 | 1
>> 13 | 4
>> 12 | 3
>> 12 | 8
>> ...
>>
>> --
>> Maxime
>> _______________________________________________
>> 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

Re: SOLVED: Combining / agglomerating / clustering numbers of adjacent polygons

2009-11-05T00:31:13Z

Derek,

FWIW -- this is a bit faster and shorter to write than your last step. You
probably won't notice the difference until you start dealing with huge
geometry collections.

--REVISED LAST STEP
create table
agglom_areas
as
SELECT (ST_Dump(the_geom)).geom As split_geom
FROM temp_f;

---YOUR LAST STEP--

create table
agglom_areas
as
select
st_GeometryN
(
the_geom,
generate_series(1,st_NumGeometries(the_geom))
) as split_geom
from
temp_f;

Leo
-----Original Message-----
From: postgis-users-bounces@...
[mailto:postgis-users-bounces@...] On Behalf Of Derek
Jones
Sent: Wednesday, November 04, 2009 10:26 PM
Cc: PostGIS Users Discussion
Subject: [postgis-users] SOLVED: Combining / agglomerating / clustering
numbers of adjacent polygons

Dear all,

I solved the problem with just a handful of lines of SQL in the end... :-P

Kinda roundabout thinking but it worked. Here's the solution:

grid_squares contains my reduced grid set from the complete grid overlay
from a previous select - it's the density table. I also previously removed
singletons from it with a check for any grid entries that had 0 touching
entities.

# Break out the multipolygon grids into polygons

create table
temp_e
as
select
st_GeometryN
(
the_geom,
generate_series(1,st_NumGeometries(the_geom))
) as split_geom
from
grid_squares;

# Break out the polygons into linestrings and agglomerate into areas #
Becomes one big area as a multipolygon so ...

create table
temp_f
as
select
st_buildarea
(
st_collect
(
st_ExteriorRing(split_geom)
)
) as the_geom
from
temp_e;

# ... afterwards, break out into polygons again # each of which is the
clustered set of # polygons comprising the outer boundary agglomeration # of
the original grid areas.

create table
agglom_areas
as
select
st_GeometryN
(
the_geom,
generate_series(1,st_NumGeometries(the_geom))
) as split_geom
from
temp_f;

I can probably with a little work reduce the steps but I don't have a need
to at this point.

This does exactly what I wanted - hope it's useful perhaps to others in the
same jam. Appreciate the help given in any event.

Now I can use the generated areas to get me some centroids and then both
intersect and then cluster the "other" data set I have which is 10s of 1000s
of points and different to this one but related to it.

Thank you again. Always useful to bounce these kinds of things around...

Kind regards

Derek Jones
_______________________________________________
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

Re: query question

2009-11-04T23:08:54Z

Thanks Maxime,

That worked!

However now I see another problem.

Some polygons are touching in a way they shouldn't. This is a problem of our drawing department but since there are a few thousand of those objects it would be nice to query with a certain tolerance. Say, the object should overlap for at least 80%.

Well, that is too much rocket science for me at the moment.
If someone has any clue if this is possible please drop me a line.

Thanks,
Ge

--- On Wed, 11/4/09, Maxime van Noppen <maxime@...> wrote:

> From: Maxime van Noppen <maxime@...>
> Subject: Re: [postgis-users] query question
> To: "PostGIS Users Discussion" <postgis-users@...>
> Date: Wednesday, November 4, 2009, 3:56 AM
> G. van Es wrote:
> > I want to have a list of wich geometry of a certain
> type is touching or crossing another type.
> >
> > Can someone point me in the right direction?
>
> Hi,
>
> If I understand your problem you want to find for each
> geometry in your
> table which geometries intersect with it ?
>
> This can be done with the ST_Intersects function and an
> self-join.
> Something like :
>
> SELECT t1.type, t2.type FROM T t1, T t2 WHERE t1.type !=
> t2.type AND
> ST_Intersects(t1.the_geom, t2.the_geom);
>
> This will generate an output like :
>
> t1.type | t2.type
> -----------------
> 13 | 12
> 13 | 1
> 13 | 4
> 12 | 3
> 12 | 8
> ...
>
> --
> Maxime
> _______________________________________________
> 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

SOLVED: Combining / agglomerating / clustering numbers of adjacent polygons

2009-11-04T19:25:40Z

Dear all,

I solved the problem with just a handful of lines of SQL in the end... :-P

Kinda roundabout thinking but it worked. Here's the solution:

grid_squares contains my reduced grid set from the complete grid overlay
from a previous select - it's the density table. I also previously
removed singletons from it with a check for any grid entries that had 0
touching entities.

# Break out the multipolygon grids into polygons

create table
temp_e
as
select
st_GeometryN
(
the_geom,
generate_series(1,st_NumGeometries(the_geom))
) as split_geom
from
grid_squares;

# Break out the polygons into linestrings and agglomerate into areas
# Becomes one big area as a multipolygon so ...

create table
temp_f
as
select
st_buildarea
(
st_collect
(
st_ExteriorRing(split_geom)
)
) as the_geom
from
temp_e;

# ... afterwards, break out into polygons again
# each of which is the clustered set of
# polygons comprising the outer boundary agglomeration
# of the original grid areas.

create table
agglom_areas
as
select
st_GeometryN
(
the_geom,
generate_series(1,st_NumGeometries(the_geom))
) as split_geom
from
temp_f;

I can probably with a little work reduce the steps but I don't have a
need to at this point.

This does exactly what I wanted - hope it's useful perhaps to others in
the same jam. Appreciate the help given in any event.

Now I can use the generated areas to get me some centroids and then both
intersect and then cluster the "other" data set I have which is 10s of
1000s of points and different to this one but related to it.

Thank you again. Always useful to bounce these kinds of things around...

Kind regards

Derek Jones
_______________________________________________
postgis-users mailing list
postgis-users@...
http://postgis.refractions.net/mailman/listinfo/postgis-users

Re: [PostGIS] #175: 'SRID=26915; POINT(482020.9789850 4984378.)' fails to parse

2009-11-04T12:54:26Z

Just wanted to express my appreciation for the fix. Thanks folks!

Reid

On 11/04/2009 02:37 PM, PostGIS wrote:

> #175: 'SRID=26915;POINT(482020.9789850 4984378.)' fails to parse
> ---------------------------+------------------------------------------------
> Reporter: rpriedhorsky | Owner: pramsey
> Type: defect | Status: closed
> Priority: low | Milestone: postgis 1.4.1
> Component: postgis | Version:
> Resolution: fixed | Keywords:
> ---------------------------+------------------------------------------------
> Changes (by pramsey):
>
> * status: new => closed
> * resolution: => fixed
>

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Re: ST_TRANSFORM function problem

2009-11-04T11:20:43Z

> Hi Folks,
>
> I'm having a problems with the transform process at present some records in
> my database.
> I try to transform my geometry in a 4326(EPSG:4326) projection to
> 900913(google mercator) projection uses a ST_TRANSFORM postgis function.
> In some geometries in same table(relation) it's work but in others postgis
> show me this erro.
>
> ********** Error **********
> ERROR: transform: couldn't project point: -14 (latitude or longitude
> exceeded limits)
> SQL state: XX000
> Context: SQL statement "SELECT ST_TRANSFORM( $1 ,900913)"
>
> What could be wrong since the geometry is valid and postgis
> metadata(spatial_ref_sys and geometry_columns) is correct?
> Environment description
>
> PostgreSQL 8.3.5 on x86_64-centOS-linux-gnu, compiled by GCC gcc (GCC) 4.1.2
> 20071124 (Red Hat 4.1.2-42)
> PostGIS 1.3.3 USE_GEOS=1 USE_PROJ=1 USE_STATS=1
> PROJ Rel. 4.6.1, 21 August 2008
> GEOS 3.0.3-CAPI-1.4.2
>

Would it be possible that your initial data (or some of them) are
stored as lat-lon, instead of lon-lat as it is expected by Postgis?
Could you isolate the points in error and send them to the list ?

Nicolas
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ST_TRANSFORM function problem

2009-11-04T10:54:38Z

Hi Folks,

I'm having a problems with the transform process at present some records in my database.
I try to transform my geometry in a 4326(EPSG:4326) projection to 900913(google mercator) projection uses a ST_TRANSFORM postgis function.
In some geometries in same table(relation) it's work but in others postgis show me this erro.

********** Error **********
ERROR: transform: couldn't project point: -14 (latitude or longitude exceeded limits)
SQL state: XX000
Context: SQL statement "SELECT ST_TRANSFORM( $1 ,900913)"

What could be wrong since the geometry is valid and postgis metadata(spatial_ref_sys and geometry_columns) is correct?

Environment description

PostgreSQL 8.3.5 on x86_64-centOS-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20071124 (Red Hat 4.1.2-42)
PostGIS 1.3.3 USE_GEOS=1 USE_PROJ=1 USE_STATS=1
PROJ Rel. 4.6.1, 21 August 2008
GEOS 3.0.3-CAPI-1.4.2

Hopes for help!

Rafael Soto

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Re: Combining / agglomerating / clustering numbers of adjacent polygons

2009-11-04T06:14:29Z

Dear Matias

Thanks for the thought. Any help is always appreciated.

I actually am using this agglomeration (when I eventually derive it ;-)
) to seed kmedoids or kmean centroids for statistical clustering, (doing
it in R via a variety of methods to see what works best). I already have
a much larger set of points that need to be clustered around the set of
centroids I generate from this grid agglomeration process.

However doing this gridding and agglomeration process first gives me a
twofold advantage, in that it not only gives me the centroid for the
clustering of the "other" data set, but also allows me to identify the
actual spatial areas in which some of my (statistical) cluster points
(in the other data set) should fall to start with, so I will do at least
one level of spatial intersection, then one level of statistical
clustering on top.

I am at this point favoring doing the grid agglomeration
programmatically - perhaps I can get that done today. (Unless anyone
comes up with an SQL solution before I finish coding it up ;-))

I'll let you folks know if I make the programmatic approach work but I'm
still open to other input in the meantime.

Thanks to all for suggestions thus far.

Kind regards

Derek.
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Re: Combining / agglomerating / clustering numbers ofadjacent polygons

2009-11-04T06:03:35Z

Derek,

I work with a "use case" similar for Site Specific Farming.
Right now I'm using statistical clustering without spatial relations.
After the clustering i use spatial relationship just to adjust the
result.
I'm interested in using spatial factor in the clustering, I'm not
experts in statistics but perhaps I can help you.

Good Luck.

Matías

On Wed, Nov 4, 2009 at 5:02 AM, Paragon Corporation <lr@...> wrote:

> Derek,
>
> Which version of PostgreSQL are you using?
>
> Interestingly we are demonstrating some of these kinds of exercises in our
> upcoming book "PostGIS in Action" book well actually we are in the middle of
> writing those chapters now -- and cleaning up some of our examples - so they
> aren't quite ready to disseminate without a lot of explanation. But all
> these tricks require the new PostgreSQL 8.4 window function and/or recursive
> query (common table expression) functionality.
>
> Sound like the recursive query might be closer to what you want (where you
> keep on accumulating based on some condition and then start a new bucket).
> There are also several techniques for creating on the fly grids in PostGIS
> which would help out here.
>
> Hope that helps,
> Regina
>
>
> -----Original Message-----
> From: postgis-users-bounces@...
> [mailto:postgis-users-bounces@...] On Behalf Of Derek
> Jones
> Sent: Tuesday, November 03, 2009 5:27 PM
> To: postgis-users@...
> Subject: [postgis-users] Combining / agglomerating / clustering numbers
> ofadjacent polygons
>
> Dear list,
>
> I have been using postgres/postgis for some years, and written a fair amount
> of spatial SQL and pgsql and R and Perl based queries.
>
> However, I've hit a brick wall in my thinking (November time change ;-)
> perhaps? ) and wondered if someone could suggest a method to help out.
>
> I have a spatial data set that varies in density across a region.
>
> I have constructed a grid (did it in qgis) and overlayed on the region, and
> then derived the density of items per grid area.
>
> Where the density is >= 3 per area, I retain the grid square in a new table.
>
> Then I want to combine the grid squars to form a larger region and (then
> incidentally to this question) find the centroid of that region where the
> grid areas touch. Singletons are rejected, and, if, say, I had 10000
> original grid squares, I might end up with 1000 clusterings of squares
> unioned together of arbitrary eventual shapes.
>
> Touching here - adjacency - could mean colinear or diagonal with 2 minimum.
> The maximum # of adjacent grid squares could run to 1000s per unioned area.
>
> But, I'm having a hard time to think through how to write the query.
>
> There are no columns in common across the grid squares, otherwise it'd be an
> easy st_union where col_xyz = 'PQR' kind of select, but all I have is the
> spatial adjacency.
>
> I've looked through the archives for the past couple of days, and perhaps
> I'm just using the wrong search criteria but I haven't seen anything that
> helps.
>
> I can see how to do this programmatically by agglomerating clusters and
> deleting from the remaining set as I go (and if I did that I would probably
> export the data and do it externally because it's quite a large data set),
> but I was really wanting to write a query for it and let it chug.
>
> Any thoughts?
>
>
> Kind regards
>
> Derek Jones.
>
>
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>
>
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--
Lic. Matías Massigoge
Cel: 54-11-62047686
www.agerpro.com.ar
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