The purpose of PnIndex in the IfcTriangulatedFaceSet

Developers
1

Hi Experts,

I would like to know the purpose of PnIndex in the IfcTriangulatedFaceSet.

As shown in the image below, I could use CoordIndex directly to find the points in the CoordList, because the list of PnIndex is a list with ascending number (1, 2, 3, 4……). Is PnIndex not necessary to my case?
image
For my case, one IfcTriangulatedFaceSet has its corresponding IfcCartesianPointList3D. Could several
IfcTriangulatedFaceSets share the same IfcCartesianPointList3D by using PnIndex?

2

Your interpretation sounds correct. Yes, if your PnIndex is ascending, it may be omitted. See this doc description:

If the PnIndex is not provided the indices point directly into the IfcCartesianPointList3D.

I would agree that you can indeed share IfcCartesianPointList3D using PnIndex.