[OpenSCAD] Origami ship has Manifold problem

Marius Kintel marius at kintel.net
Sun Apr 26 16:44:20 EDT 2015


On Apr 26, 2015, at 06:10 AM, kitwallace <kit.wallace at gmail.com> wrote:

> I think the problem boils down to unioned spheres at different angles
> sphere(20);
> rotate([0,40,0]) sphere(20);
> 
The problem is that CGAL uses infinite precision when calculating unions. When converting back to floating point, some vertices get collapsed. Such collapsing may affect topology, and in this case it collapses a very small volume into a plane, similar to this: https://github.com/openscad/openscad/issues/1042#issuecomment-70279505

This breaks the manifoldness pre-condition for reading files back into CGAL (thus breaking import) and it trips manifold checks in external software.

To fix this we should post-process CGAL results to fix degenerate cases, or better; use a different CSG library.

 -Marius





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