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

Jordan Brown openscad at jordan.maileater.net
Thu Nov 14 13:42:26 EST 2019

On 11/14/2019 7:32 AM, arnholm at arnholm.org wrote:
> I think self-intersections are almost always a sign of something else
> gone wrong, it is typically a body that overlaps itself and and not a
> result of a boolean operation. A self-overlapping volume is physically
> impossible. There are lots of ways to use bodies that are not
> 2-manifold, but a self overlapping volume seems like an obvious mistake.

Is it?

Consider the 2D case.  I'm drawing with a paintbrush, and so I'm drawing
areas, not lines.  I draw a figure-8.  It's self-intersecting, but it's
clearly not impossible.  The two parts of the stroke are unioned.

If we view the 3D equivalent as painting in 3D with a 3D brush, the
result doesn't seem impossible at all.

If we were drawing with voxels, I suspect that the question wouldn't
even arise.
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