[OpenSCAD] Discuss manifoldness, co-incident faces edges etc

Parkinbot rudolf at digitaldocument.de
Sun Nov 17 20:27:30 EST 2019

This is an interesting, but endless discussion. In my eyes the cause (and the
possible solution) of the problem is somewhere else, and language
immediately makes it clear:

nophead wrote
> So with 2 cubes sharing an edge,

You speak about *two* cubes, but you want to get a single physical object in
order to have a 2-manifold. And indeed, the union of two cubes which don't
have any region, edge, or vertex in common are treated as a *single*
2-manifold - and not as a list of 2-manifolds describing physical objects
that have nothing in common. This is for logical (and representational)
reasons of course, but it is also the source of all evil. Having the union
operation returning a list of continuous objects would solve the problem.
Also if two cubes are sharing an edge, because you can just put them both
into the list as individual continuous objects.  

It would be easy to represent such a list, if STL format allowed multiple
solid/endsolid sections, but the file format never grew out from from its
being a provisional solution. Of course this only mirrors the common
implementations of libraries and programs, like the ones used by OpenSCAD. 

Sent from: http://forum.openscad.org/

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