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Creating an Arc
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Creating an Arc
by Sling Blade
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Hi,
I need to create an Arc in a shape file. Is this possible using shapelib? My understanding is that only points, polylines and polygons can be created so what I probably need is a way to convert an Arc to a collection of Polylines, is that correct? Does any one have an example of creating Arcs they can share with me? Regards _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib |
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Re: Creating an Arc
by Frank Warmerdam-2
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Scott Ferguson wrote:
> Hi, > > I need to create an Arc in a shape file. Is this possible using shapelib? My > understanding is that only points, polylines and polygons can be created so > what I probably need is a way to convert an Arc to a collection of > Polylines, is that correct? > > > Does any one have an example of creating Arcs they can share with me? Scott, You are correct that shapefiles cannot store curved arcs. The normal technique is to approximate them as polylines. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@... light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib |
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Re: Creating an Arc
by Sling Blade
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You are correct that shapefiles cannot store curved arcs. The normal technique is to approximate them as polylines. What would be great would be to learn how to approximate an Arc with Polylines. Do you have any code showing how this is done? Regards |
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Re: Creating an Arc
by Frank Warmerdam-2
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Sling Blade wrote:
> > You are correct that shapefiles cannot store curved arcs. The normal > technique is to approximate them as polylines. > > > What would be great would be to learn how to approximate an Arc with > Polylines. Do you have any code showing how this is done? > > Regards Sling, There is some example code for converting arcs to polylines in: http://svn.osgeo.org/gdal/trunk/gdal/ogr/ogrsf_frmts/oci/ogrocistroke.cpp A lot depends on how your arcs are defined. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@... light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib |
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Re: Creating an Arc
by Sling Blade
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Thanks Frank!
I could make better sense of it if I could see the includes too, or at least see the OGRLineString class. Would it be possible for you to post them, or you could email them directly to me if that is preferred? Thanks again for your help Regards, -----Original Message----- From: shapelib-bounces@... [mailto:shapelib-bounces@...] On Behalf Of Frank Warmerdam Sent: Tuesday, July 28, 2009 2:36 PM To: Shapelib Development Subject: Re: [Shapelib] Creating an Arc Sling Blade wrote: > > You are correct that shapefiles cannot store curved arcs. The normal > technique is to approximate them as polylines. > > > What would be great would be to learn how to approximate an Arc with > Polylines. Do you have any code showing how this is done? > > Regards Sling, There is some example code for converting arcs to polylines in: http://svn.osgeo.org/gdal/trunk/gdal/ogr/ogrsf_frmts/oci/ogrocistroke.cpp A lot depends on how your arcs are defined. Best regards, -- ---------------------------------------+------------------------------------ -- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@... light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib |
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Re: Creating an Arc
by Frank Warmerdam-2
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Scott Ferguson wrote:
> Thanks Frank! > > I could make better sense of it if I could see the includes too, or at least > see the OGRLineString class. > > Would it be possible for you to post them, or you could email them directly > to me if that is preferred? Scott, It is all part of GDAL/OGR (http://www.gdal.org). But since the code is not written in terms of SHPObject you are going to have to do a bunch of restructuring. So best to treat this code as an example and avoid dragging in the actual classes references. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@... light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib |
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Re: Creating an Arc
by Sling Blade
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>Scott,
>It is all part of GDAL/OGR (http://www.gdal.org). >But since the code is not written in terms of SHPObject you are going to >have >to do a bunch of restructuring. So best to treat this code as an example >and >avoid dragging in the actual classes references. I'll go over it and see how far I get. I was hoping this was a common question with an obvious answer :-) Thanks again Frank you've been a huge help! Regards, -----Original Message----- From: shapelib-bounces@... [mailto:shapelib-bounces@...] On Behalf Of Frank Warmerdam Sent: Tuesday, July 28, 2009 3:31 PM To: Shapelib Development Subject: Re: [Shapelib] Creating an Arc Scott Ferguson wrote: > Thanks Frank! > > I could make better sense of it if I could see the includes too, or at least > see the OGRLineString class. > > Would it be possible for you to post them, or you could email them directly > to me if that is preferred? Scott, It is all part of GDAL/OGR (http://www.gdal.org). But since the code is not written in terms of SHPObject you are going to have to do a bunch of restructuring. So best to treat this code as an example and avoid dragging in the actual classes references. Best regards, -- ---------------------------------------+------------------------------------ -- I set the clouds in motion - turn up | Frank Warmerdam, warmerdam@... light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib |
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shpproj help
by Ken S. Elvehjem
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Hi,
I have a set of shapefiles that are in what I have always been told are "unprojected longitude & latitude." X & Y coordinates are in decimal degrees ( -92.5173861 x 42. 9431848) with a datum of WGS84 I am trying to use shpproj to convert these files to UTM Zone data (Zone 15, in my example) for some further analysis. The following don't work: shpproj jack jackson-soils-UTM -i=geographic -o="proj=utm zone=15 units=m" shpproj jack jackson-soils-UTM -o="proj=utm zone=15 units=m" The processis aborted with the note, "unable to process projection, exiting" I suspect that some data files may be missing, but I have no way of figuring that out. BTW, the "proj" directive "works" but doesn't give me any good clues either. Any suggestions would be greatly appreciated. Ken _______________________________________________ Shapelib mailing list Shapelib@... http://lists.maptools.org/mailman/listinfo/shapelib |
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