Best practice for multi-material IfcProducts

Hi all,

I’m developing an application to render IFC models. So it is very important that I can associate materials (not styles) with every piece of geometry in the model. I’ve been testing my approach with the Schependomlaan model and I’ve run into problems with the IfcProducts that consist of multiple materials, such as windows and doors. All I got for those is an IfcMaterialList, which is useless as far as I understand in identifying which IfcRepresentationItem is associated with which material.

I have a lot of unanswered questions:

  • Have I missed something? Is there a way to associate materials in an IFcMaterialList with IfcRepresentationItems?
  • What would be the recommended practice to deal with multi-material IfcProducts in IFC2? So far I’ve encountered models where a all items of an door are distributed across multiple IfcDoors, or such as in the Schependomlaan example where an IfcMaterialList is used. Is there a way to represent an IfcProduct with multiple items, each with an associated material?
  • And how would that work in IFC4? I’ve been trying to make sense out of the IfcShapeAspect diagram. Do I understand correctly that instead of a ‘Body’ representation the IfcWindow in the diagram would have multiple IfcProductDefinitionShapes, each with a name stored in an IfcShapeAspect?

Thanks for helping me out in advance.