Giles Bathgate

@nophead True, in-fact @kintel and I recently tried to get to the bottom of this. He has a patch that removes zero-area triangles, which seems to fix a lot of...

@nophead Yeah self intersections: ``` c# polyhedron([[0,0,0],[0,10,0],[10,10,0],[10,0,0]],[[0,1,3,2]]); ``` Are definitely bad. Arguably my previous examples are "bad" too, you can't export them, or do anything much with them in OpenSCAD...

@nophead The error there is converting from CGAL's Polyherdon3 representation to NefPolyhedron3, So the problem isn't that that shape cannot be represented, its that the construction is wrong. Consider the...

@nophead In anwser to your question the boolean operations work as one would expect, the intersection of two lines is a point, the intersection of a sphere and a plane...

hmm, Yet this works: ``` c# difference() { union() { polyhedron([[0,0,0],[0,10,0],[5,5,0]],[[0,1,2]]); polyhedron([[10,0,0],[5,5,0],[10,10,0]],[[0,1,2]]); } cylinder(); } ```

@doug-moen There is no limitation on what STL can represent vs what AMF can represent, ultimately these file formats represent triangles. STL just uses a list of vertexes and repeats...

@doug-moen Here is your non manifold shape in STL https://gist.github.com/GilesBathgate/79450ae7f51a990f3883

I think what most people care about is whether they can load these files into their slicer. The above loads into Slic3r and it seems to think its manifold :/...

@MichaelAtOz The CGAL alpha shapes module as you suggested seems to be fit for this purpose. I've thrown together a proof of concept implementation based on this: https://stackoverflow.com/questions/38829464/cgal-concave-hull-3d-alpha-shapes-3 It seems...

This problem also effects my project, I would be very interested in a solution such as that proposed in https://github.com/CGAL/cgal/pull/451 being adopted.