Can opening element geometry have _any_ material associated with it?

IfcOpeningElement is not allowed to have a material association. It can have representation items with materials/colors, though. Should we be respecting these materials/colors on import?

I think this is an interesting question. Some geometry libraries are indeed able to apply the material/color of the 2nd operand to the boolean result where the subtraction occurred.

I didn’t find any word on this in the specification. I would be inclined to say we should not. A physical interpretation of this would be that some sort of surface finishing is applied to the void (?). I’d say that is relevant information then that needs to be supplied semantically such as IfcCovering or IfcSurfaceFeature.

It would be a good time to ask around though what the implementations are currently doing. (IfcOpenShell-based applications for one would not be able to apply it).

I tend to agree with the interpretation that any materials applied to voids should be ignored - they don’t make sense other than for display.

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I would also be inclined to disregard such presentation colors/styles. As @aothms said, the only use I could see is in Boolean operations (which in my understanding is however not too reliable).