[OpenSCAD] lookup_halfedge(): input error - explanation please ?

Daniel K. Schneider Daniel.Schneider at unige.ch
Tue Mar 23 18:52:41 CET 2010


Hi,
Could some nice soul explain what this means:
Quote from 
http://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids :

"Note that OpenSCAD currently crashes if your polygons are not all 
oriented the same way; pay attention to the vertex ordering."

I understand about crashing I mean, but don't know what "oriented the 
same way means". I thought I did, e.g.
I managed to create a simple 3 triangle shape (inserted the picture in 
the wiki page above). I also know how to create the same shape by 
extrusion or difference, but I just want to do it "by hand", once :)

A pointer to some text about "polygon orientation" made for non-CS, 
non-math, non-3D people is fine enough :)

Here is my case:

polyhedron
   (points = [
          [0, -10, 60], [0, 10, 60], [0, 10, 0], [0, -10, 0], [60, -10, 
60], [60, 10, 60],
          [10, -10, 50], [10, 10, 50], [10, 10, 30], [10, -10, 30], [30, 
-10, 50], [30, 10, 50]
          ],
    triangles = [
         [0,2,3],   [0,1,2],  [0,4,5],  [0,5,1],   [5,4,2],  [2,4,3],
                 [6,8,9],  [6,7,8],  [6,10,11], [6,11,7], [10,8,11],
         [10,9,8], [0,3,9],  [9,0,6], [10,6, 0],  [0,4,10],
                 [3,9,10], [3,10,4], [1,7,11],  [1,11,5], [1,7,8], 
                 [1,8,2],  [2,8,11], [2,11,5]
         ]
    );

Trace:
CGAL::Polyhedron_incremental_builder_3<HDS>::
lookup_halfedge(): input error: facet 13 shares a halfedge from vertex 2 
to vertex 6 with facet 12.
CGAL error: assertion violation!
Expression : check_protocoll == 0
File       : /usr/local/include/CGAL/Polyhedron_incremental_builder_3.h
Line       : 198
Explanation:
Refer to the bug-reporting instructions at 
http://www.cgal.org/bug_report.html
Aborted

A picture (before OpenSCAD crashes) is here:
http://edutechwiki.unige.ch/en/File:Openscad-polyhedron-example3.png

- thanx - Daniel

PS: Added some stuff to the wikibook, i.e. a few pictures and a few 
precisions.
http://en.wikibooks.org/wiki/OpenSCAD_User_Manual/2D_to_3D_Extrusion
http://en.wikibooks.org/wiki/OpenSCAD_User_Manual/STL_Export
My goal is to make a (simple duplo factory) and I need a support element 
that is as simple
as possible (difference objects do not sit well next to other cubes ...)

-- 
Dr Daniel K.Schneider, TECFA (Educational Technologies and Learning)

TECFA    (TEchnologies de Formation et Apprentissage)
FPSE     (Faculté de Psychologie et des Sciences de l'Education)
Université de Genève
54 Route des Acacias, CH-1227 Carouge

email: Daniel.Schneider at unige.ch
www:   http://tecfa.unige.ch/tecfa-people/schneider.html
       http://edutechwiki.unige.ch/

Tel: 41 22 379 9377 - Fax: 41 22 379 9379




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