[OpenSCAD] GROUP vs UNION

Alan Cox alan at lxorguk.ukuu.org.uk
Wed Feb 8 11:10:52 CET 2012


On Wed, 8 Feb 2012 00:18:28 +0000
nop head <nop.head at gmail.com> wrote:

> Well STL files are intended to represent physical objects to be made on a
> 3D printer. Physical objects are always manifold. What is the meaning / use
> of a mesh with overlapping shells?

Firstly physical objects are not always manifold.. solids are (almost,
but we'll leave that to the quantum physicists). Secondly a lot of other
things where STL is useful for modelling purposes are decidedly non
manifold (consider modelling clearances for a set of moving parts, the
parts *can* overlap providing they don't exist in the same place at the
same moment, so the set of clearances are non manifold when you model
their full extent)

You can do a lot more with an STL model that print widgets.


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