Join the Patches into MCad Structure ? (or reverse: "split")

Splitting is easy, but joining is sure not. You cant join arbitrary surfaces. In the structure expected by Mathcad's 3D plot, two patches (plane quadrilaterals, 2x2 matrices) must have exactly one edge in common. This means that most arbitrarily chosen surfaces can't be connected at all and I imagine it is quite time-consuming and difficult to write a function which checks a bunch of patches to see if they can be connected at all and then sew them together.