I am using IfcProduct.Transform() method to obtain the transformation matrix (XbimMatrix3D instance) and using that to do conversions between relative and absolute placements.
But I am not able to find those functions in Ifc4 namespace! I am not able to find anything else that is meant to substitute these functions. This issue has been highlighted here too: https://github.com/xBimTeam/XbimGeometry/issues/103, but there is no response. Please help!
It looks like this all got refactored in the IFC4 updates so that transforms on IfcObjectPlacements are handled in Xbim.Geometry.Engine against interfaces in Xbim.Ifc4.Interfaces
I'd take a look at https://github.com/xBimTeam/XbimGeometry/blob/08920df29f909dde0c4f65c63d80ae0b5540025f/Xbim.Geometry.Engine.Interop/XbimGeometryEngine.cs#L442