Perhaps Tibor might have some easier suggestions, but this is a difficult problem from past experience. The only way to be sure of the window opening shape is to compare the 3D body of the wall with
the opening, probably necessitating making a copy of the wall (and probably connected/cutting elements). This can yield a list of polygons that make up the opening, but note that:
- The opening on the wall inside might be different to the outside
- If the wall is curved, both the inside and outside openings will multi-facetted (echoing the wall faces).
Ralph Wessel BArch