Trimmed surface

Hi,

Would you help me to solve next problem:

A trimmed NURBS surface, if I well know, is created in next way: - create Geom_BSplineSurface - create topological object over it TopoDS_Face - create topological outer wire object - add outer wire to TopoDS_Face object (Add() function). (Is it correct?) I would like to perform intersections of plane with trimmed surface. I made some tests, but I always obtained intersections with original not trimmed surface. Help, please.

Best regards, Adrian