CGAL users discussion list

[Gilbert Bernstein <>]

Stephen,

The mesh you're trying to read in is non-manifold.  This is probably  
why it is not working.  Inside of the triangular prism is a second  
triangular prism sharing part of a face.  The surface represented  
itself is non-manifold, and your data file contains T-Junctions, so  
the connectivity of the mesh isn't made explicit.  One or both of  
these problems might be the cause of a bad conversion.

If you check the examples folder, there is a program called  
"complex_construction.cpp"  It demonstrates the use of the following  
function:

#include<CGAL/OFF_to_nef_3.h>

Nef_3 N;
std::size_t discarded = CGAL::OFF_to_nef_3 (std::cin, N, true);

discarded contains the number of facets of the model which were  
discarded by the conversion process.  You might want to try running  
the model through complex_construction and see what happens.

-- Gilbert


On Jan 12, 2008, at 7:47 PM, Stephen Wong wrote:

Hi there,

On this seemingly innocent input solid in the form of a OFF file,  
CGAL's Nef_polyhedron_3 constructor using Polyhedron_3 crashes.  I  
believe that the solid represented by the OFF file is valid based on  
the specification (you can see the model in geomview or any other OFF  
viewer).  I caused this crash by modifying the Nef_3.sln's  
interface_polyhedron:

Polyhedron P ;
std::ifstream fin( "Triangle - Copy.off" ) ;
fin >> P ;
if ( P.is_closed() && P.is_valid() )
{
  Nef_polyhedron_3 N1( poly ) ;
}

Thanks,

Stephen
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<Triangle - Copy.off>