[OpenSCAD] F5 works, but F6 gives: ERROR: CGAL error in CGAL_Nef_polyhedron3():

arnholm at arnholm.org arnholm at arnholm.org
Thu Jan 18 03:27:20 EST 2018


On 2018-01-17 23:34, Ronaldo Persiano wrote:
> Here is another interesting case. The hull is a tetrahedron but the
> inside polyhedron was defined with just one face ( a simple list of
> all vertices). It is surprising that the preview of the polyhedron
> alone is correct but the preview of the intersection with the sphere
> is void.
> 
>> intersection(){
>> hull(){
>>    polyhedron( points=[[0,0,0],[0,10,0],[10,10,0],[0,0,10]],
>>                faces =[[0,1,3,2]]);
>>    }
>>    sphere(8); // the preview is correct when this line is commented
>> }

Since faces are of no interest in the context of hull() this works. But 
the single face is totally warped, i.e. points not in the same plane. 
According to
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/The_OpenSCAD_Language#polyhedron
this should be an error:
"Points which describe a single face must all be on the same plane."

Perhaps one could also say that a polyhedron with fewer than 4 faces is 
always an error, perhaps with the exception of zero faces in the case of 
using it within hull()?

Carsten Arnholm




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