Overlap between IfcAdvancedBrep, IfcFacetedBrep, IfcTessellatedFaceSet and its subtypes

The following entities have some similarities:
IfcAdvancedBrep
IfcAdvancedBrepWithVoids
IfcFacetedBrep
IfcFacetedBrepWithVoids
IfcTessellatedFaceSet
IfcPolygonalFaceSet
IfcTriangulatedFaceSet
Therefore the question is if some of these entities can be merged. IfcAdvancedBrep (IfcAdvancedBrepWithVoids) are clearly semantically the most rich concepts. If these entities would be replaced by the others semantic information will be lost, the most close here would be IfcPolygonalFaceSet. Also the other way around removing IfcPolygonalFaceSet or IfcTriangulatedFaceSet would prevent storing some of the basic geometry representations and a clean way to define individual triangle / face color assignment.

IfcFacetedBrep allows advanced representations of how faces are build up, via curved polygons, trimmed polygons etc. as does its subtype entity supporting openings. Therefore this entity has extra value over tessellated representations. The other way around tessellated entities are able to represent knowledge in much more condense and easy manner to process.

The bottom line is that all these 7 entities have their own clear benefits and my opinion would be to keep them separate and not merge them.

Start by reviewing the seven IFC entities named in the issue and their subtype definitions. No file, test, or entry point is identified; a contribution would first need a decided scope for whether they remain separate or are merged, plus criteria for validating the schema change.

Written by the indexing model from the issue text.