Ok so as a branch from here PMVC I've started looking at GMVC - General Mean Value Coordinates These coordinates are in 2D for now and I'm hoping to extend them into 3D using the same technique as in the PMVC stuff, why? just cos, and because the one limitation in PMVC is that the control cage needs to be triangles, GMVC takes that limitation away and will still be a positive value coordinate system for convex polys (i.e quad mesh control cages) that should with a bit of luck lead to even smo