Determine which faces of intersection body were originally open to the air?

marena_richardson

I have two rectangular blocks positioned perpendicular to each other in an L shape so they overlap. I used opBoolean to get the intersection block. Now I want to know which faces of the intersection block were in the middle of the original two blocks and which two were originally the ends of the two blocks. Is that possible? How would I do that?

kevin_o_toole_1

It would be tricky, and I doubt it could be made to be robust. An intersection between two arbitrary bodies will likely have no "exposed" faces, and it may be useful to think about what should happen in such a case. I honestly can't think of a good mechanism for guessing a reference frame that wouldn't annoy me when it guesses wrong. So if it were me, I'd use at least one directional input.

If you do want this behavior, you can write some logic which checks for pairs of coincident faces between the original bodies, since
that's the only starting condition that results in "exposed" faces in the intersection. See Jacob's question for how to check if planes are coincident.