How to extract a center point of a building in CityGML?

CityGML has a complex structure for sure and is annoyingly flexible which means a building can have no geometryand still be valid.... And indeed getting the Centerpoint which seems trivial can be quite complex.

The best option I think here is to aggregate the buildings using the hierarchy option. The Aggregator transformer lets you choose ids and parent ids on which to structure a geometry hierarchy. Here you can use gml_id and parent_gml_id.

If you ignore the CityModel feature type and feed in everything to the aggregator you should get out one aggregate for each building.

This method is nice because you don't need to worry about missing or multiple ground surfaces or LOD's etc.​

After this you can pretty easily ​extract the bounds and create a 3D bounding volume or calculate the center point based on bounds.

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