CGAL users discussion list

[Joe C <>]

Hi,

I am getting crash while performing 3D difference. When I searched for the forum, I found this old thread which I copied below. It seems that this issue still exists (I'm using fairly recent release CGAL 3.6.1). Any solution to this?

Joe


*****************************************************************
The following is the contents from the old thread:

Hi there,

 

I have encountered a crash during execution of boolean operations on a data set.  The assertion is below.

 

CGAL error: assertion violation!

Expr: itl != it->second.end()

File: $(CGALROOT)\include\CGAL/Nef_3/SNC_external

_structure.h

Line: 567

 

If the assertion is ignored, a null-pointer reference occurs in make_twins() a few lines below that code.  I have attached the offending files, and a modification of the example “interface_polyhedron” program that demonstrates this error.  The kernels I have used are Cartesian<Gmpq> and Exact_predicates_exact_constructions_kernel.  I know the input files are ugly (a.off is pretty ugly), but they pass is_valid() and is_closed()/is_simple() tests both in Polyhedron_3 and Nef_polyhedron_3.

 

If anyone can provide any more details regarding how to avoid this kind of error, or why this is happening, I am glad to hear it!

 

Thanks,

 

Stephen

//#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Gmpq.h>
#include <CGAL/Cartesian.h>
#include <CGAL/Polyhedron_3.h>
#include <CGAL/IO/Polyhedron_iostream.h>
#include <CGAL/Nef_polyhedron_3.h>
#include <CGAL/IO/Nef_polyhedron_iostream_3.h>
#include <iostream>
#include <fstream>

typedef CGAL::Cartesian<CGAL::Gmpq>  Kernel;
typedef CGAL::Polyhedron_3<Kernel>  Polyhedron;
typedef CGAL::Nef_polyhedron_3<Kernel> Nef_polyhedron;
typedef Kernel::Vector_3  Vector_3;
typedef Kernel::Aff_transformation_3  Aff_transformation_3;

Polyhedron* loadPolyFromFile( const char* file )
{
   std::ifstream fin( file ) ;
   if ( !fin.is_open() ) return NULL ;

   Polyhedron* p = new Polyhedron() ;
   fin >> *p ;

   if ( p->is_closed() && p->is_valid() )
   {
      // Only return when closed and valid.
      return p ;
   }
   else
   {
      delete p ;
      return NULL ;
   }
}

void savePolyToFile( const Polyhedron& p )
{
   std::ofstream fout( "out.off" ) ;
   fout << p ;
   fout.close() ;
}

int main()
{
   Polyhedron* p1 = loadPolyFromFile( "a.off" ) ;
   Polyhedron* p2 = loadPolyFromFile( "a2.off" ) ;
   Polyhedron* p3 = loadPolyFromFile( "b.off" ) ;

   if ( !p1 || !p2 || !p3 )
   {
      std::cerr << "Error loading files..." << std::endl ;
      exit( 1 ) ;
   }

   Nef_polyhedron n1( *p1 ) ;
   if ( !n1.is_simple() || !n1.is_valid() )
   {
      std::cerr << "n1 is not a 2-manifold." << std::endl ;
      exit( 1 ) ;
   }
   Nef_polyhedron n2( *p2 ) ;
   if ( !n2.is_simple() || !n2.is_valid() )
   {
      std::cerr << "n2 is not a 2-manifold." << std::endl ;
      exit( 1 ) ;
   }
   Nef_polyhedron n3( *p3 ) ;
   if ( !n3.is_simple() || !n3.is_valid() )
   {
      std::cerr << "n3 is not a 2-manifold." << std::endl ;
      exit( 1 ) ;
   }
   Nef_polyhedron n = n1 - n2 - n3 ; // <-- Crashes here...

   if ( n.is_simple() )
   {
      Polyhedron p ;
      n.convert_to_Polyhedron( p ) ;
      savePolyToFile( p ) ;
   }
   else
   {
      std::cerr << "N1 is not a 2-manifold." << std::endl;
   }

   // Clean up.
   delete p1 ;
   delete p2 ; 
   delete p3 ;
   exit( 0 ) ;
}

Attachment: b.off
Description: Binary data

Attachment: a2.off
Description: Binary data

Attachment: a.off
Description: Binary data