CGAL users discussion list

[Pierre Cagne <>]

Hi,

I currently use the facilities of CGAL about line arrangements, and I'm 
experiencing an issue. When I want to insert a segment line whose the 
endpoints are already vertices of the graph, I'm having that kind of error :

  terminate called after throwing an instance of 
'CGAL::Precondition_exception'
    what():  CGAL ERROR: precondition violation!
  Expr: ! is_degen
  File: /usr/macports/include/CGAL/Arr_segment_traits_2.h
  Line: 149
  Explanation: Cannot contruct a degenerate segment.
  Abort trap

Here is a minimal example code to get this error :

#include <iostream>
#include <CGAL/Cartesian.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arrangement_2.h>
#include <CGAL/Gmpz.h>
#include <CGAL/Gmpq.h>

using namespace std;

typedef CGAL::Gmpz                                                            
        NT;
typedef CGAL::Gmpq                                                            
        rat;
typedef CGAL::Cartesian<rat>                                                  
  Kernel;
typedef CGAL::Arr_segment_traits_2<Kernel>                       Traits_2;
typedef Traits_2::Point_2                                                     
         Point_2;
typedef Traits_2::X_monotone_curve_2                                   
Segment_2;
typedef CGAL::Arrangement_2<Traits_2>                                
Arrangement_2;

int main(void) {
  Arrangement_2 arr;

  CGAL::insert(arr, Segment_2 (Point_2 (rat(0),rat(0)), Point_2 
(rat(1),rat(1))));
  CGAL::insert(arr, Segment_2 (Point_2 (rat(1/4),rat(1/2)), Point_2 
(rat(1),rat(0))));
  CGAL::insert(arr, Segment_2 (Point_2 (rat(0),rat(0)), Point_2 
(rat(1/4),rat(1/2))))
  
  return 0;
}


I kind of understood that point-location query might help me, but after 
several trials, I'm still at the same point (without pun :) ).

So, does anyone know how to do it ?



Thankfully.

--
Pierre Cagne
Etudiant à l'ENS de Paris
Département Informatique