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

Carsten Arnholm arnholm at arnholm.org
Wed Nov 13 15:33:55 EST 2019

On 13.11.2019 21:05, nop head wrote:
> There is no guesswork needed to read an STL if the geometry it contains 
> is manifold. 

I am sorry but this is nonsensical. See below.

> If STL files had a rule to say the geometry they contained has to be 
> manifold and writers and readers enforced it there would not be a problem.

How many times must it be explained that STL is a polygon soup without 
any topological information whatsoever, and hence any topology 
(manifoldness relates to topology only) on the reader side must be 
guessed? It has been stated many times already. It is a fact.

> OpenSCAD doesn't reject bad STLs. It just feeds the soup to CGAL and 
> CGAL barfs if it is not manifold and produces and incomprehensible 
> exception. 

And in this process, someone takes a guess at what the topology is 
supposed to be.

Carsten Arnholm

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