[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
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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