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

nop head nop.head at gmail.com
Sun Nov 17 03:25:51 EST 2019


> I frequently ran into non-manifold conditions, and also due to (I
believe) the small number problem, producing self intersections.

The problem is OpenSCAD snaps to a grid and then stores the result as a
polygon soup. That can create non-manifold geometry whenever there are very
close vertices. It is a massive bug to truncate vertex coordinates and not
fix the mesh.

On Sun, 17 Nov 2019 at 07:29, <arnholm at arnholm.org> wrote:

> On 2019-11-17 00:33, Michael Marx wrote:
> > As Doug said 'STL can't represent curved surfaces, it can only
> > represent a polyhedral approximation'.
>
> That's true of anything that comes out of OpenSCAD or any other mesh
> based modeller, it is nothing particular to STL, OBJ, OFF, AMF or
> whatever format you choose. A mesh representation is a finite
> approximation, of course it is.
>
> It is not the file format, is the core modeller.
>
> If you took the CGAL library and replaced it with another library based
> on CAD BREP style datastructure, for example OpenCASCADE
> https://dev.opencascade.org/ the situation would be different, and you
> could output STEP files or other formats with accurate respresentation
> of curved geometry. But as long as the core model is a mesh
> representation, the output will be a polyhedral approximation.
>
> Carsten Arnholm
>
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