[gdal-dev] OSGeo.OGR.Layer.Clip in C# application

[Ellis Robin (Bundaberg)]

As an update, this would appear to be a topological issue with my input
shapefile. I can successfully complete Intersection processes using the
method described previously if I use simple data inputs. Similarly, I
can complete a Clip process on simple data inputs, although the results
aren't always entirely as expected. If I hook up the
GDALProgressFuncDelegate I do notice this message pops up during
intersection/clip of complex inputs:

 

'System.ApplicationException' occurred in ogr_csharp.dll

 

Which ultimately leads to the GEOMETRYCOLLECTION error reported
previously. I can only assume that clean topology will avoid this.

 

Regards

 

Rob

 

From: gdal-dev-bounces at lists.osgeo.org
[mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Ellis Robin
(Bundaberg)
Sent: Friday, 13 December 2013 10:32 AM
To: gdal-dev at lists.osgeo.org
Subject: [gdal-dev] OSGeo.OGR.Layer.Clip in C# application

 

I'm working in Win 7 x64 and  VS2010 using gdal/ogr compiled libraries
in a C# project (libraries from 'release-1600-x64-dev.zip', built
12/12/2013). I can successfully open two polygon shapefiles as
'DataSource' objects, however when I attempt to clip one shapefile by
the other I get this error message:

 

Attempt to write non-polygon (GEOMETRYCOLLECTION) geometry to POLYGON
type shapefile

 

My code is posted below, any assistance appreciated. I'm happy to read
more documentation/examples if somebody can point me in the right
direction.

 

Thanks very much

 

Rob

 

public static Layer clipAGdalDSByAnother(DataSource baseDS, DataSource
clipDS)

{

    Layer baseLayer = baseDS.GetLayerByIndex(0);

    Layer clipLayer = clipDS.GetLayerByIndex(0);

 

    string newDataName = "tester.shp";

 

    Layer layer;

 

    int i;

    for (i = 0; i < baseDS.GetLayerCount(); i++)

    {

        layer = baseDS.GetLayerByIndex(i);

        if (layer != null && layer.GetLayerDefn().GetName() ==
newDataName)

        {

            Console.WriteLine("Layer already existed. Recreating
it.\n");

            baseDS.DeleteLayer(i);

            break;

        }

    }

           

    Layer result = baseDS.CreateLayer(newDataName, null,
baseLayer.GetLayerDefn().GetGeomType(), new string[] { });

 

    baseLayer.Clip(clipLayer, result, new string[] { "SKIP_FAILURES=YES"
}, null, null);

 

    return result;

}

 

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