[gdal-dev] GML driver - gfs geometry type values and supported GML geometry types

[Johannes Echterhoff]

Even,
Thank you, that was very helpful. Then I’ll map Curve to CompoundCurve and Surface to CurvePolygon.
The possible reason, that this may be due to a lack of mapping between OGR and QGIS geometry types, is quite intriguing. I tried to find out more on the web, and came across https://github.com/qgis/QGIS/blob/master/src/core/providers/ogr/qgsogrprovider.cpp (if that is the right place to look for the actual code), but could not find out more about the implemented mapping. Oh well, it’s ok.
Again, thanks, and best regards,
Johannes

Von: Even Rouault <even.rouault at spatialys.com>
Gesendet: Donnerstag, 5. Januar 2023 15:13
An: Johannes Echterhoff <echterhoff at interactive-instruments.de>; gdal-dev at lists.osgeo.org
Betreff: Re: [gdal-dev] GML driver - gfs geometry type values and supported GML geometry types


Johannes,

this is more an issue on QGIS side, in its OGR provider where there's likely a lack of mapping between the OGR geometry types and QGIS geometry types for Curve and Surface (just guessing, didn't check). The root cause is that Curve and Surface in OGC/ISO specs are abstract types only, not directly instantiable. So it is really hard to have datasets where they are reported as layer geometry types, unless you try hard to do so, as you did. I'd suggest you use CurvePolygon (resp. CompoundCurve) instead of Surface (resp. Curve) in your .gfs file. That's what the OGR XSD reader does when encountering a gml:SurfacePropertyType or gml:CurvePropertyType. Those are instanciable types and QGIS should behave properly

Even
Le 05/01/2023 à 14:00, Johannes Echterhoff a écrit :
Hi,

The GML driver shows behavior that I do not understand: When I load a feature with a gml:Polygon, which, in the gfs file, is defined with GeomPropertyDefn/Type = Surface, then the geometry does not appear to be understood. At least when I try to load the data in QGIS 3.28.0, then the layer has an unknown geometry type. If, on the other hand, I set GeomPropertyDefn/Type to “Polygon”, “MultiPolygon”, or even “MultiSurface”, the geometry is recognized. Same problem if the feature has a gml:LineString as geometry, and I declare it as GeomPropertyDefn/Type = Curve.

What am I missing here? :-)

Is there some documentation available that sheds light on which gfs geometry type values support which GML geometry types?

Best regards,
Johannes



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