Slightly Un developable surfaces

I’ll try to explain some general issues: Rhino should not unroll surfaces with compound curvature, BUT it will unroll any surface which is at least linear in one direction (u/v). Then it does not even check the Gaussian curvature (which is a bug IMHO) and it simply _Smash-es the surface. It will report the difference in area of the curved and unrolled surface, but in rare cases it may happen that stretching and compressing cancels out. Rhino will not unroll surfaces where the “ruling-lines” do not follow one of the NURBS directions (u/v) no matter if the Gaussian Curvature is zero overall.

_Squish should be used to flatten slightly un-developable surfaces but you’ll have to take care about the topology. You may search the forum for squish failures and bugs to see some examples which it does not like. It helps to know that squish creates a mesh under the hood and uses that to calculate the deformation. Looks like meshes created with the new _QuadRemesh command in V7 work pretty good with _Squish. The optional parameters in _Squish are nice but can be tricky. Of course you cannot expect to “preserve the boundaries” length and use “stretch mostly” on a saddle surface (negative Gaussian curvature).

_Smash is most flexible and will flatten almost any surface. But if you cannot Squish it, then _Smash probably will not help much for your kind of work. However it should also work with trimmed surfaces so if you have an example which does not work then please post it.