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<kintel>
Hey all. Recent advances in geometry processing, in particular by switching to Manifold, has made it possible to both represent and process corner cases which we'd previously barf on, things like two cubes sharing a face, or geometry folding back onto itself.
<InPhase>
Excellent.
<kintel>
Most of this has been made possible by separating topology from spatial positioning, and building topologically manifold objects by splitting coincident vertices into multiple logically separate (but still co-incident) vertices
<kintel>
This is only possible when using file formats where positions and connectivity is separate (3MF, OBJ, OFF etc.). For legacy formats like STL, we can partially work around this by attempting to reconstruct a valid manifold topology through connectivity analysis.
<kintel>
Now one question: Does anyone possess examples or STL files, which OpenSCAD still struggles to import due to manifoldness issues? I'm not talking about plain broken STL, but anything that has collapsed vertices, touching parts, microscopic cracks etc.
<ali1234>
how does a bad import actually manifest?
<kintel>
Bad import: If you try to perform a CSG op with a good object, the result becomes an empty object
<ali1234>
i only have examples where it takes forever
<kintel>
heh, forever is a different challenge. Not trying to address that yet :)
<ali1234>
now i think about it, i think i have seen empty objects in the past - and i fixed it by slightly moving one of the objects
<ali1234>
i may have been using CGAL though
<kintel>
yeah, cgal is a lot less forgiving as we don't have a good intermediate format to import through
<ali1234>
this didn't involve any import
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