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I have a series of shapefiles, that have 3D geometries (ie: points ZM). I would like to remove the 3D geometry so that the files are 2D. Is there a way to remove 3D geometry from a shapefile using OGR?

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  • Technically, shapefiles with elevation values and measures are 4-D, not 3-D.
    – Vince
    Commented Oct 14, 2015 at 18:07
  • Is it enough to update Z and M to zero or do you want that the type of the shapefile is changed into POINT?
    – user30184
    Commented Oct 14, 2015 at 19:21
  • My preference would be to have the geometry as a point, not a pointZM
    – Ryan Garnett
    Commented Oct 14, 2015 at 19:28
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    Then simply write a new shapefile as ogr2ogr -f "ESRI Shapefile" output_2d.shp input_zm.shp -dim 2 gdal.org/ogr2ogr.html. However, I do not know if it works if you really has POINTZM shapefile because GDAL does not support M gdal.org/drv_shapefile.html. Let's hope it just skips M values.
    – user30184
    Commented Oct 14, 2015 at 19:34
  • Thank you! I was wondering if the -dim was referencing geometry
    – Ryan Garnett
    Commented Oct 14, 2015 at 19:44

2 Answers 2

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Write your data into a new shapefile with ogr2ogr and force geometry type into 2D with the -dim switch.

ogr2ogr -f "ESRI Shapefile" output_2d.shp input_zm.shp -dim 2

The -dim setting is not limited to shapefiles but works in the same way for most vector formats. One exception I know is Oracle Spatial that does not honour the ogr2ogr switch but you must use the layer specific -lco DIM=2instead.

http://gdal.org/ogr2ogr.html

http://www.gdal.org/drv_oci.html

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Once your shapefile is read as ogr.Geometry, you can use its flattenTo2d() method.

See the GDAL documentation.

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