The simplest case would be, one side has two collinear edges [A,B] and [B,C], and the other side has edge [F,G] such that F/A and G/C are coincident. The implementation works by adding a matching vertex to [F,G], via an edge split at the projected location of B, to create a new vertex X that could be welded with B. F A F A So basically it | | | | turns this | B into this one X B configuration | | | | G C G C