I just replied about this on one of your other threads. But you can try Trimble.Vce.Gem.dll, the class you're looking for is Model3D, that may have a method that lets you do this sort of calculation, or a way to create difference surfaces (like a cut/fill surface). You might try messaging Gary Lantaff directly and see if he'll get back to you on it, he's a surface guru.
Quan
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