[OpenSCAD] STL problem - globoid worm gear system

Marius Kintel marius at kintel.net
Mon Jan 1 12:34:44 EST 2018

> On Jan 1, 2018, at 11:43 AM, Parkinbot <rudolf at parkinbot.com> wrote:
> I wouldn't mix up mesh repair for input and mesh coarsing for output. 
> For output, where you start with a supposedly valid representation, [...]

One of the initial challenges is to effectively obtain such a valid representation. When using CGAL, this comes as Nef3 polyhedrons with fractional (Gmpq) coordinates. Teasing out a reasonable mesh data format from this is already an annoying problem. Converting from Gmpq to something more manageable (like double precision floats) already introduces topology issues. If we try to run this algorithm _after_ converting to doubles, the problem is basically the same as incoming mesh repair. If we were to solve this in fractional space, we would have a few more freedoms, but even then, an edge collapse isn’t topology-preserving and we’d still need some good heuristics or neighborhood analysis to select valid edges for collapse, and then introduce another cleanup algorithm to deal with the leftover edges.

..or go the other way like Carsten did and base the algorithms on edge splits, and accept that incoming meshes may have been destroyed by an earlier coarsening step.

Anyway, this is all stuff we’d love to get to - just significant work to implement and test.


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