[gdal-dev] ogr.Geometry - UnionCascaded() question

[Even Rouault]

Le mardi 16 septembre 2014 19:43:43, Max Demars a écrit :
> Hi,
> 
> I want to do a union on many ogr.Geometry stored in a list, but I have a
> TypeError: unbound method UnionCascaded() must be called with Geometry
> instance as first argument (got list instance instead).
> 
> I though UnionCascaded was made to perform Union on many geometries like
> this:
> 
>         geometries = []
>         for feature in featureCollection['features']:
> 
> geometries.append(ogr.CreateGeometryFromJson(json.dumps(feature['geometry']
> ))) outputGeometry = ogr.Geometry
>         output = outputGeometry.UnionCascaded(geometries)
> 
> How am I supposed to use this function if list are not accepted?

Max,

UnionCascaded() takes no argument and operates on a multipolygon geometry :

For example

geom = ogr.CreateGeometryFromWkt('MULTIPOLYGON(((0 0,0 1,1 1,0 0)),((0 0,1 1,1 
0,0 0)))')
result = geom.UnionCascaded()

Or you can build it into several steps :

geom = ogr.Geometry(ogr.wkbMultiPolygon)
geom.AddGeometry(ogr.CreateGeometryFromWkt('POLYGON((0 0,0 1,1 1,0 0))'))
geom.AddGeometry(ogr.CreateGeometryFromWkt('POLYGON((0 0,1 1,1 0,0 0))'))
result = geom.UnionCascaded()

Best regards,

Even

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