As part of 0.6 refactoring

Aims:

1. Abstraction to have a OpenCascade-agnostic interface
   • To allow for a mesh based kernel (e.g. CGAL). OpenCascade carries a lot of overhead for simple faceted geometries in IFC. A hybrid BRep-mesh based approach would alleviate the remaining performance bottlenecks
   • Companies might want to use proprietary geometry kernels for reliability and integration with their products
2. Maintain IFC-instance to TopoDS_Shape mapping
   • IfcGeom::IfcRepresentationShapeItem (a {placement, shape, style}-tuple) not particularly granular. E.g material overrides for specific faces within a shell cannot be recorded.
   • Now, faces with boolean results from operands with different styles cannot retain association to original operand and therefore loose style association.
   • Provides benefits in advanced visualisation where e.g an IfcCartesianPoint of a IfcPolyline in an IfcExtrudedAreaSolid can be traced back to the IFC instance.

Implementation:

Mesh based

To be determined

Open Cascade

Every operation results in a TopoDS_Compound and a mapping of TopoDS_Shape -> IfcRepresentationItem*. At the moment of triangulation, individual faces can retrieve their IfcSurfaceStyle from the mapping.