trim and join breps

Hi all!

I'm having some issues using the Brep.Trim and Brep.MergeBreps methods. Im working on a script that generates vertical section curves of a terrain including the buildings standing on it. The buildings shouldn't overlap the terrain because the curves should be continuous polylines in the end, therefore the terrain should trim the buildings and the terrain should have a spare whole delimitated by every building. I tried to use the above mentiones methods to first trim the buildings with the terrain and then "cut out" wholes in the terrain where buildings are standing. The resulting breps have to be joined together in order to get one open brep. I managed to run the script once, later I got an "index out of range error" without really figuring out why the breps aren't cut any more.

Thx for help and suggestions)

Best

H.