Forcing a geometry type as output doesn't seem to work on multipolygons

theroggy commented 3 weeks ago

What is the bug?

When gdal.VectorTranslate with option geometryType is ran on a file with (also) multipolygons, for most geometrytypes being specified the conversion is not happening:

For MULTILINESTRING and MULTIPOINT the conversion would lead to something sensible but it isn't happening.
For LINESTRING and POINT nothing is happening either, and there it is not super clear what would be sensible to do. However, maybe a conversion to MULTILINESTRING and MULTIPOINT is more logical than just keeping the MULTIPOLYGON?

PS: Sorry for the stupid bug reports, but I'm cleaning up warnings in my unit tests ;-)...

Steps to reproduce the issue

from osgeo import gdal

gdal.UseExceptions()

for geometrytype in ["MULTILINESTRING", "LINESTRING", "MULTIPOINT", "POINT"]:
    options = gdal.VectorTranslateOptions(geometryType=geometrytype)
    ds_output = gdal.VectorTranslate(
        srcDS="/vsicurl/https://github.com/geofileops/geofileops/raw/main/tests/data/polygon-parcel.gpkg",
        destNameOrDestDS=f"C:/temp/force_type_{geometrytype}.gpkg",
        options=options,
    )

Versions and provenance

Windows 11 with gdal 3.9.2 installed from conda-forge

Additional context

No response

rouault commented 3 weeks ago

You are running into implementation limits of https://gdal.org/en/latest/doxygen/ogr__api_8h.html#a4e5f995d159279739909196d45ba09e5 . The doc doesn't say much as this would be extremely tedious. The doc is looking at the implementation for all (source, target) tuples that are implemented

theroggy commented 3 weeks ago

I had a look at the more specified functions that are probably used by ForceTo.

Indeed, for e.g. for ForceToPolygon: the doc mentions polygons will be changed to a collection of linestrings (one per ring). , but MultiPolygons are not mentioned at all... so implicitly it seems to be behaving according to the documentation...

OSGeo / gdal