There are plenty of available GIS datasets available in e.g. Shapefile, GeoPackage, CSV. Those dataset can be used to enrich the existing CityGML 3D building models.
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Conversion from 2D Building Footprint to LoD1-CityGML
The 2D building footprint can be converted to the 3D building models in CityGML format. The height attribute is necessary as an input parameter to extrude each building.
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