CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Hello,

First of all, sorry for the delay.


Is the attached patch solving your problem?


S.

Lehtonen, Matti/HIIT wrote:
> HI!
>
> Versions of files:
> // $URL:
> svn+ssh://scm.gforge.inria.fr/svn/cgal/branches/CGAL-3.5-branch/Surface_mesh_simplification/include/CGAL/Surface_mesh_simplification/halfedge_collapse_Polyhedron_3.h
> $
> // $Id: halfedge_collapse_Polyhedron_3.h 50078 2009-06-25 15:12:52Z fcacciola 
> $
>
> // $URL:
> svn+ssh://scm.gforge.inria.fr/svn/cgal/branches/CGAL-3.5-branch/Surface_mesh_simplification/include/CGAL/Surface_mesh_simplification/Detail/Edge_collapse_impl.h
> $
> // $Id: Edge_collapse_impl.h 50078 2009-06-25 15:12:52Z fcacciola $
>
>
> Sympton:
> The border were broken after edge collapse, even the border were constrained.
> See:
> http://picasaweb.google.fi/mmalehtonen/SimplificationBorderNotHonored?authkey=Gv1sRgCKTirofBua60GQ&feat=directlink
>
> Description:
> In Edge_collapse_impl.h, line 358, an edge is rejected if vertices P *and* Q 
> are
> on border allowing case were vertex P is on border and vertex Q is not (and
> vice-versa). However, in halfedge_collapse_Polyhedron_3.h, lines 145-150, 
> vertex
> P is always removed without checking.
>
> Correct fix:
> In halfedge_collapse_Polyhedron_3.h it should be checked that vertex P isn't 
> on
> border and vertex Q should be removed instead, if P is on border. However, it 
> is
> currently impossible, because vertex_descriptor don't have is_border() method 
> or
> it is next to impossible to call bool EdgeCollapse<...>::is_border(...) for
> vertex.
>
> Quick fix:
> In Edge_collapse_impl.h, line 358, change "&&" to "||" or reject edges that 
> have
> any vertex on border. However, this prevents edges to be collapsed by removing
> vertex Q.
>
> Lehtonen, Matti
>
>
> Quoting "Lehtonen, Matti/HIIT" 
> <>:
>
> > Codebase: plain 3.5.1
> >
> > Sympton:
> > I have simplified surfaces extracted from C3T3 volume(s). For some reason, I
> > cannot get borders honored (not modified during simplification process), even
> > thought they should be.
> >
> > See:
> http://picasaweb.google.fi/mmalehtonen/SimplificationBorderNotHonored?authkey=Gv1sRgCKTirofBua60GQ&feat=directlink
> > Question: How to solve this problem?
> >
> > Code samples:
> > * Simplification:
> > int r = CGAL::Surface_mesh_simplification::edge_collapse( P,
> >           stop,
> >           CGAL::vertex_index_map( boost::get( CGAL::vertex_external_index, P 
> > ) )
> >           .edge_index_map  (boost::get(CGAL::edge_external_index, P ) )
> >           .edge_is_border_map( constrains_map )
> >           .get_cost(
> > CGAL::Surface_mesh_simplification::Edge_length_cost<Polyhedron>()
> > )
> >           .get_placement(
> > CGAL::Surface_mesh_simplification::Midpoint_placement<Polyhedron>() )
> >           .visitor( vis ) );
> >
> > * Constraint map:
> > reference
> > operator[]
> > (
> >  key_type const &   e
> > )
> > const
> > {
> >  key_type const &   oe = opposite_edge( e, polyhedron );
> >  return e->is_border() ||
> >         /* Without opposite edge checking, even less is honored */
> >         oe->is_border() /* ||
> >         is_constrained( e ) || is_constrained( oe ) */;
> > }
> >
> > * stop predicate:
> > bool
> > operator()
> > (
> >  FT const &         aCurrentCost    __attribute__((unused)),
> >  Profile const&     aEdgeProfile    __attribute__((unused)),
> >  size_type              aInitialCount   __attribute__((unused)),
> >  size_type              aCurrentCount   __attribute__((unused))
> > )
> > const
> > {
> >  return aCurrentCost > _aParam ;
> > }
> >
> >
> > Data files:
> https://docs.google.com/uc?id=0B0XXln5ZRT1xMTczZWFkMmQtNTJjNy00MzA3LTg2MzgtYmIyMjNiYjJkZjU0&authkey=CMCXweAE&hl=en
> > Thx,
> > Lehtonen, Matti
> >
> > Researcher, head programmer - Helsinki Institute for Information Technology
> > HIIT
> > http://www.hiit.fi/
> > --
> > Life is complex. It has real and imaginary parts.
>
>
> Researcher, head programmer - Helsinki Institute for Information Technology 
> HIIT
> http://www.hiit.fi/

Index: include/CGAL/Surface_mesh_simplification/Detail/Edge_collapse_impl.h
===================================================================
--- include/CGAL/Surface_mesh_simplification/Detail/Edge_collapse_impl.h	(revision 60712)
+++ include/CGAL/Surface_mesh_simplification/Detail/Edge_collapse_impl.h	(working copy)
@@ -713,7 +713,7 @@
   // (PT and QB are removed if they are not null).
   // All other edges must be kept.
   // All directed edges incident to vertex removed are relink to the vertex kept.
-  rResult = halfedge_collapse(aProfile.v0_v1(),mSurface);
+  rResult = halfedge_collapse((is_border(aProfile.v0())?opposite_edge(aProfile.v0_v1(),mSurface):aProfile.v0_v1()) ,mSurface);
 
   CGAL_SURF_SIMPL_TEST_assertion_code( -- lResultingEdgeCount ) ;