CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Try with the attached file.

Sebastien.


On 03/24/2012 11:38 AM, Zohar wrote:
> 1.
> http://cgal-discuss.949826.n4.nabble.com/Contibution-for-CGAL-Complex-3-in-triangulation-3-polyhedron-builder-h-td2307832.html
>
> 2.
> A. It converts tets from CGAL to tets for vtk, I'm not sure how it could
> help me.
> B. But there is the
> MeshComplex_3InTriangulation_3::Facets_in_complex_iterator(), which gives
> the surface facets. I can't see a link (?) to what the facet consists of,
> but I assume there's a begin_vertices(), or I can look in the source for
> that.
> C. I could hold in an std::map the vertex handles to some arbitrary ids, so
> I could connect between common vertices of the facets.
> D. I can use c3t3.surface_patch_index(Facet f), to retrieve the connected
> component the facet belongs to - if that's what I think it is, and here
> things get a bit murky. I'm not fully sure about the definitions, or what's
> going on here, and that's why I implied that a depiction might help. There
> are two related links in the manual:
>
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Mesh_3/Chapter_main.html
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Mesh_3_ref/Concept_MeshComplex_3InTriangulation_3.html
>
> On the second link, second paragraph:
>
> "To distinguish the faces of the embedded 3D complex from the faces of the
> triangulation, we call the faces of the embedded complex respectively
> subdomains, for 3D faces and surface patches, for 2D faces, while the
> triangulations faces are called respectively cells, facets, edges and
> vertices."
>
> I'm not sure if it's bad punctuation, but there's a problem in this sentence
> and it doesn't make sense to me.
>
> Please help me understand the c3t3 structure. It's a 3 simplicial complex,
> which is embedded as a triangulation. The simplicial complex is partitioned
> to a few spaces (sub-domains?), each space is composed of tets, and its
> boundary surface is composed of facets. Referring to the first link, figure
> 50.1, I assume that each colored set of tets is an independent space.
> Are there facets only on the surface, since a tet is also made of 4 facets?
> Why do we need to distinguish between the simplicial complex and its
> embedding - the triangulation?
> When I extract a polyhedron, I want only facets that touch 'air', and not
> the ones between the spaces, how do I know if a facet touches air?
> When I reconstruct a c3t3 from a poly, how many spaces will I have?
>
> 3.
> I thought it was buggy officially. Anyway here is one of the standard
> models, try to remesh it with poly_3 demo:
>
> http://svn.code.sf.net/p/mymayaplugins/code-0/trunk/tmp/camel.off
>
> --
> View this message in context: 
> http://cgal-discuss.949826.n4.nabble.com/Convert-C3t3-to-Polyhedron-tp4467182p4501152.html
> Sent from the cgal-discuss mailing list archive at Nabble.com.

// Copyright (c) 2008-2009  GeometryFactory (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
// You can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation,
// either version 3 of the License, or (at your option) any later version.
//
// Licensees holding a valid commercial license may use this file in
// accordance with the commercial license agreement provided with the software.
//
// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
//
// $URL: svn+ssh:///svn/cgal/branches/next/Mesh_3/include/CGAL/IO/Complex_3_in_triangulation_3_to_vtk.h $
// $Id: Complex_3_in_triangulation_3_to_vtk.h 67117 2012-01-13 18:14:48Z lrineau $
//
//
// Author(s)     : Laurent Rineau

#ifndef BOUNDARY_OF_SUDDOMAIN_OF_COMPLEX_3_IN_TRIANGULATION_3_TO_OFF_H
#define BOUNDARY_OF_SUDDOMAIN_OF_COMPLEX_3_IN_TRIANGULATION_3_TO_OFF_H

#include <map>
#include <sstream>

#include <CGAL/array.h>

namespace CGAL {

namespace internal{
template <class Vertex_handle>
std::size_t get_vertex_index(Vertex_handle v,std::map<Vertex_handle, std::size_t>& V,std::size_t& inum,std::stringstream& vertex_buffer){
  std::pair<typename std::map<Vertex_handle, std::size_t>::iterator,bool> res=
    V.insert(std::make_pair(v,inum));
  if (res.second){
    ++inum;
    vertex_buffer <<   res.first->first->point().point() <<"\n"; //point is weighted!
  }
  return res.first->second;
}
}//namespace internal

template <typename C3T3>
std::ostream&
output_boundary_of_c3t3_to_off(const C3T3& c3t3, 
                               typename C3T3::Subdomain_index sd_index,
                               std::ostream& output)
{
  typedef typename C3T3::Triangulation Triangulation;
  typedef typename Triangulation::Vertex_handle Vertex_handle;

  const Triangulation& tr = c3t3.triangulation();

  std::map<Vertex_handle, std::size_t> V;
  
  std::size_t inum = 0; 
  std::size_t nfacets = 0;
  cpp0x::array<std::size_t,3> indices={{0,0,0}};
  std::stringstream facet_buffer,vertex_buffer;
  for(typename C3T3::Facets_in_complex_iterator 
        fit = c3t3.facets_in_complex_begin(),
        end = c3t3.facets_in_complex_end();
      fit != end; ++fit) 
  {
    typename C3T3::Subdomain_index cell_sd=c3t3.subdomain_index(fit->first);
    typename C3T3::Subdomain_index opp_sd=c3t3.subdomain_index(fit->first->neighbor(fit->second));
    
    if (cell_sd!=sd_index && opp_sd!=sd_index) continue;

    ++nfacets;
    int j=-1;
    
    
    for (int i = 0; i < 4; ++i)
      if (i != fit->second)
          indices[++j]=internal::get_vertex_index((*fit).first->vertex(i), V, inum,vertex_buffer);
    if ( (cell_sd==sd_index) == (fit->second%2 == 1) ) std::swap(indices[0],indices[1]);
    facet_buffer << "3" << " " << indices[0] <<" " << indices[1] <<" " << indices[2] << "\n";
  }
  
  output << "OFF " << inum << " " << nfacets << " 0\n";
  output << vertex_buffer.str();
  output << facet_buffer.str();
  
  
  return output;
}

} // end namespace CGAL

#endif // BOUNDARY_OF_SUDDOMAIN_OF_COMPLEX_3_IN_TRIANGULATION_3_TO_OFF_H