I have this problem.
I Have surfaces (triangles) which looks like an extruded surface. (with a ground layer and a layer above)
like feature looks like coming out from an Extruder transformer.
Which transformer i use to get only the "roof" layer (the highest layer or thickness)...so in my opinion to delete all triangles which goes from roof to ground level.
I dont know if i use the right english words to explain my problem.
Greetz
Franco