[gdal-dev] confused about coordinate dimension

[Daniel Baston]

Hi Rich,

I'm sure there's a historical reason for this, but it looks like GDAL has
two very similar methods: GetCoordinateDimension() and
CoordinateDimension(). The former, rather surprisingly, returns only 2 or
3. The latter one returns the value you're looking for:

>>> from osgeo import ogr
>>> g = ogr.CreateGeometryFromWkt('POINT ZM (1 2 3 4)')
>>> g.CoordinateDimension()
4
>>> g.GetCoordinateDimension()
3

Dan

On Mon, Jun 29, 2026 at 2:45 PM Richard Greenwood via gdal-dev <
gdal-dev at lists.osgeo.org> wrote:

> In Python, I want to find the coordinate dimension of my source. For
> example, with a postgis table with geometry(MultiLineStringZM,4326). My
> Python:
>
> in_lyr = in_ds.ExecuteSQL(select)
> feature0 = in_lyr.GetNextFeature()
> feature0_geom = feature0.GetGeometryRef()
> feature0_geom.GetGeometryType()        # 3005
> ogr.GeometryTypeToName(3005)            #  '3D Measured Multi Line String'
> feature0_geom.GetCoordinateDimension()  # 3
>
> Based on:
> https://gdal.org/en/stable/api/vector_c_api.html#_CPPv425OGR_G_CoordinateDimension12OGRGeometryH
> I am expecting the coordinate dimension to be 4. Am I approaching this
> incorrectly?
>
> --
> Richard W. Greenwood
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> gdal-dev at lists.osgeo.org
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>
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