Summary

These surfaces and skins were constructed in pure openSCAD, thanks to support for computation provided in versions since late 2014.

The code is on Github https://github.com/KitWallace/openscad/blob/master/poly_surface.scad and the project is discussed in my blog http://kitwallace.tumblr.com/post/111959789244/computed-surfaces-in-openscad

http://www.thingiverse.com/thing:24897 also constructs surfaces but because it uses unions of small cuboids, it is rather slower.

Be aware that there is no check on sanity so faces can be reversed with dire effects on subsequent CSG operations.