CGAL users discussion list

[Martin Baeker <>]

Dear all,

yesterday I asked about modifying a vertex of a Nef_polyhedron.

By now I understand the following:
Obviously, I should use a
Nef_polyhedron::Vertex_iterator
insetad of a 
Nef_polyhedron::Vertex_const_iterator.

The only problem I have is that this does not work because
the function vertices_begin()
seems to be const, so I cannot iterate my iterator.

According to the manual, there should be a non-const version of this,
but I'm at a loss how to call it. I found that vertices_begin() is
defined in SNC_decorator.h and SNC_const_decorator.h, but *both* are
included in Nef_polyhedron_3.h 
Nef_polyhedron_3.h contains the follwoing declaration

template <typename Kernel_, typename Items_ = typename 
CGAL::Default_items<Kernel_>::Items, typename Mark_ = bool>
class Nef_polyhedron_3 : public CGAL::Handle_for< Nef_polyhedron_3_rep<Kernel_, 
Items_, Mark_> >,
                          public 
SNC_const_decorator<SNC_structure<Kernel_,Items_,Mark_> >

Is it this that is responsible for the choice? if so, how do I access
the non-const version of vertices_begin? Do I need to modify
Nef_polyhedron_3.h itself? That seems a "bit" dangerous to me...

Any help would really be appreciated, since I'm completely lost...

Martin.



                   Priv.-Doz. Dr. Martin Bäker
                   Institut für Werkstoffe
                   Technische Universität Braunschweig
                   Langer Kamp 8
                   38106 Braunschweig
                   Germany
                   Tel.: 00-49-531-391-3073
                   Fax   00-49-531-391-3058
                   e-mail 
<>

---------- Forwarded message ----------
Date: Tue, 17 Aug 2010 10:18:53 +0200 (CEST)
From: Martin Baeker 
<>
To: CGAL Mailinglist 
<>
Subject: Modifying a vertex of a Nef_Polyhedron

Dear all,

I'm trying to loop over the vertices of a Nef_Polyhedron and modify
the coordinates of one of the vertices:

      for(Nef_polyhedron::Vertex_const_iterator
          v = Cube.vertices_begin(),
              end = Cube.vertices_end();
                v != end; ++v)
                {
                  if ( v->point() ==tip)
		      v->point() = Nef_polyhedron::Point_3(0,0,0);//tip.x(), 
tip.y(), secondHeight);
                        break;
                        }

The trouble is that v seems to be const and cannot be modified, at
least that's how I understand the compiler error:

error: passing ‘const CGAL::Point_3<CGAL::Cartesian<CGAL::Gmpq> >’ as ‘this’ 
argument of ‘CGAL::Point_3<CGAL::Cartesian<CGAL::Gmpq> >& 
CGAL::Point_3<CGAL::Cartesian<CGAL::Gmpq> >::operator=(const 
CGAL::Point_3<CGAL::Cartesian<CGAL::Gmpq> >&)’ discards qualifiers

There seems to be no such thing as a non-constant Vertex-iterator - so
how can I loop over vertices in a way that I can modify their coordinates?

Any help greatly appreciated, as usual,

Martin.

PS: Here's my bunch of Definitions, just in case:

typedef CGAL::Cartesian<CGAL::Gmpq>   Kernel;
typedef CGAL::Polyhedron_3<Kernel>                           Polyhedron;
typedef CGAL::Nef_polyhedron_3<Kernel>  Nef_polyhedron;
typedef Kernel::Plane_3  Plane_3;
typedef Kernel::Ray_3  Ray_3;
typedef Kernel::Point_3    Point;
typedef Kernel::Segment_3    Segment;
typedef Kernel::Line_3    Line;
typedef Kernel::Vector_3  Vector_3;
typedef EKernel::Plane_3  EPlane_3;
typedef EKernel::Point_3    EPoint;
typedef EKernel::Vector_3  EVector_3;
typedef Polyhedron::Halfedge_handle                          Halfedge_handle;
typedef Polyhedron::Halfedge_around_facet_circulator 
Halfedge_facet_circulator;
typedef Polyhedron::Halfedge_iterator Halfedge_iterator;
typedef Polyhedron::Facet_handle                          Facet_handle;
typedef Polyhedron::Facet                          Facet;
typedef Polyhedron::Facet_iterator                   Facet_iterator;
typedef Kernel::Aff_transformation_3  Aff_transformation_3;
typedef Nef_polyhedron::Vertex_const_handle Vertex_const_handle;
typedef Nef_polyhedron::Halfedge_const_handle Halfedge_const_handle;
typedef Nef_polyhedron::Halffacet_const_handle Halffacet_const_handle;
typedef Nef_polyhedron::Volume_const_handle Volume_const_handle;
typedef Nef_polyhedron::Object_handle Object_handle;


                   Priv.-Doz. Dr. Martin Bäker
                   Institut für Werkstoffe
                   Technische Universität Braunschweig
                   Langer Kamp 8
                   38106 Braunschweig
                   Germany
                   Tel.: 00-49-531-391-3073
                   Fax   00-49-531-391-3058
                   e-mail 
<>