Insert an edges in a surface - CGAL error: assertion violation

Question

I'm creating an application using qt creator which read .off files as CGAL::Linear_cell_complex_for_combinatorial_map and preview it I want to make operations on the read mesh such as removing edge and restore it .

it shows the following error :

terminate called after throwing an instance of 'CGAL::Assertion_exception'
  what():  CGAL ERROR: assertion violation!
Expr: i != idx.end()

my code:

   filename =std::string("/home/nourhan/QT projects/cube.off");
     std::ifstream ifile(filename.c_str());
     if (ifile)
     {

   CGAL::load_off(lcc, ifile);
}

       lcc.display_characteristics(std::cout) << ", valid=" <<
         lcc.is_valid() << std::endl;

 LCC_3::Dart_handle d2=lcc.darts().begin();
   LCC_3::Dart_handle d3= lcc.insert_cell_0_in_cell_1( d2);
  lcc.insert_cell_0_in_cell_2(   d2);

       std::vector<LCC_3::Dart_handle> adarts;
       adarts.push_back(d2);
           adarts.push_back(d3);
       adarts.push_back(lcc.beta<1>(d3));

       if (lcc.is_insertable_cell_1_in_cell_2(d2, d3))
      lcc.insert_cell_1_in_cell_2( d2, d3);

       lcc.display_characteristics(std::cout) << ", valid=" <<
         lcc.is_valid() << std::endl;

  CGAL::write_off(lcc, "copy-head.off");
 }

the output : Darts=24, #0-cells=8, #1-cells=12, #2-cells=6, #ccs=1, valid=1

Darts=36, #0-cells=10, #1-cells=18, #2-cells=10, #ccs=1, valid=Map not valid: dart 0x5d7df0 does not have a vertex.

0

the output .off file :

OFF 
8 10 0

I don't know how it inserted edges successfully and the same time Map not valid and the output .off file isn't correct .

I appreciate any help .

Answer 1

The method you use, insert_cell_0_in_cell_1, is a method from combinatorial map.

This method modifies the topology of the object, inserting a new vertex, but the geometry is not updated, because a combinatorial map does not necessarily have a geometry.

There are 2 solutions:

1. you can add a point to the new vertex after the insertion, using for example set_vertex_attribute(d3, create_vertex_attribute(
2. replace the use of insert_cell_0_in_cell_1 by a method of linear cell complex, which updates both topology and geometry. You can for example use the insert_point_in_cell method.

Using one of these solutions will give you a valid linear cell complex, and thus you can export it as off file.

But, one important question is what are you trying to do ? It seems you insert some cells randomly, thus it is highly likely to obtain a very strange mesh.

Have a look once again at the examples Modification Operations of the linear cell complex package. When I insert cells, I do not take random darts but precise darts in order to do a precise operation.