@plha said: Fredo: I like that approach, as it happens, I might use this code in some other place of my silly program, it just does not solve my initial problem - to be able to select one particular face. I am trying to avoid drawing one more edge (on one of the unmarked edges of shaded face in my picture) - so I wil have unambiguos common face - but that lacks elegance a lot. You have to figure out an additional criterion then to say which face you like to have. For instance, the fact that the normals to each edge crosses within the surface, or any other condition.