Hi Marco, yeah you're right, it turns out for a case with some of the curves intersecting each other like you've got there it won't make nested holes. So for that method to work you'd need to detect curves that intersect with your outer boundary and remove those from what you give to PlanarSrf. With the intersected curves removed you could probably use PlanarSrf to detect whether a curve is either inside or outside the outline though, if your other method doesn't work out.

- Michael