Ifc object with multiple colors

Question

Is it possible, within IFC 4.0, to define an Ifc object (IFC Wall for example) with multiple colors (which are IfcStyledItem)? How can we activate each color inside a BIM Viewer program (like layer in AutoCAD)?

Thanks,

Answer 1

Formally, you can have only one IfcStyledItem per IfcRepresentationItem, but the styled item can refer to multiple presentation styles (IfcPresentationStyle). Similarly, you could have one IfcPresentationLayerWitStyle per IfcPresentationItem referring to multiple presentation styles. A viewer application could then provide user interactions to switch styles on or off per representation item or layer. However I believe that is not the right interpretation of those presentation style sets. The standard is not clear about it, but I would rather assume these styles are supposed to aggregate, that is you have both curve and fill style for example, which complement each other rather than being alternatives.

A more high-level solution and idiomatic with CAD applications is assignment on the level of the whole IfcPresentation (as opposed to the items of a presentation). If you are concerned about styles on the level of product geometry like a whole wall, that would be sufficient detail. You would do this through layer assignment. Layers then have styles and can be switched on and off. Since one presentation can be assigned to multiple layers this would likely resemble the functionality you have in mind.