adding "geometry validation" parameter to IFC4.3

a call particularly to all software implementers

in the past, we discussed at various occasions, e.g. ISG Meetings, the need to add parameters to the IFC exchange file, that allows the receiver to quickly validate, if it has rendered the geometry correctly (particularly for advanced geometry representations, such as advanced brep, advanced sweeps or CSG trees).

In IFC4 one has been added - IfcShapeRepresentation with RepresentationIdentier "CoG" as center of gravity, others were discussed, like the body volume or a bounding box.

is this sufficient, and sufficiently described?

also relates to #193, #194