CGAL users discussion list

["Andriy Fedorov" <>]

The example which is located in
CGAL/examples/Polyhedron_IO/triangulation_print_OFF.h shows how to
output a 3d triangulation into OFF format. I found that doing
something similar for 3d surface requires some (non-trivial for a
person not familiar with CGAL) changes to that code. I spent a lot of
time figuring out types and functions, so I attach the resulting code
in case someone else will be trying to solve a similar problem.

Andriy Fedorov
// Modified from $CGAL/examples/Polyhedron_IO/triangulation_print_OFF.h
// to output surface triangulation
// 
// Prints a Surface_mesh_complex_2_in_triangulation_3 with points in RAW format
// 
// RAW format is (vertex numbering starts from 0):
// <#points> <#faces>
// point_0.x point_0.y point_0.z
// ...
// face0.firstPoint face1.firstPoint face2.firstPoint
// ...
//
// Andriy Fedorov / fedorov at cs wm edu

#ifndef CGAL_TRIANGULATION_PRINT_RAW_H
#define CGAL_TRIANGULATION_PRINT_RAW_H 1

#ifndef CGAL_PROTECT_MAP
#include <map>
#define CGAL_PROTECT_MAP
#endif

CGAL_BEGIN_NAMESPACE

template < class Triang >
void
triangulation_print_RAW( std::ostream& out, 
			 Triang& triang, 
			 bool binary  = false, 
			 bool noc     = false,
			 bool verbose = false) {

    typedef typename Triang::Vertex_handle    Vertex;
    typedef typename Triang::Vertex_iterator  Vertex_iterator;
    typedef typename Triang::Facet_iterator   Face_iterator;
    typedef typename Triang::Cell_handle      Cell;

    // Build a map from vertex pointers to vertex indices.
    std::map<typename Triang::Triangulation::Point,std::size_t> mapping;
    std::size_t vn = 0;
    Vertex_iterator vi = triang.vertices_begin();
    for ( ; vi != triang.vertices_end(); ++vi) {
    	mapping[(*vi).point()] = vn;
    	vn++;
    }

/* AF: NB!!! from CGAL docs here 

 http://www.cgal.org/Manual/3.2/doc_html/cgal_manual/TriangulationDS_3_ref/Concept_TriangulationDataStructure_3.html#Cross_link_anchor_780

 "[...] Edges (1-faces) and facets (2-faces) are not explicitly represented: a facet is given by a cell
 and an index (the facet i of a cell c is the facet of c that is opposite to the vertex of index 
 i) and an edge is given by a cell and two indices (the edge (i,j) of a cell c is the edge whose 
 endpoints are the vertices of indices i and j of c).[...]"

 */

    
    // Count faces
    std::size_t fn  = 0;
    Face_iterator fi = triang.facets_begin();
    for ( ; fi != triang.facets_end(); ++fi)
    	fn++;

    out << vn << " " << fn << std::endl;
    
    vi = triang.vertices_begin();
    for ( ; vi != triang.vertices_end(); ++vi) {
	  out <<  to_double(vi->point().x()) << " " 
			  <<  to_double(vi->point().y()) << " " 
			  <<  to_double(vi->point().z()) << std::endl;
    }
    

    fi = triang.facets_begin();
    while ( fi !=triang.facets_end() ) {
      const Cell& ch = (*fi).first;
      const int& i = (*fi).second;
      for(int j=0;j<3;j++){
        const Vertex w = ch->vertex(triang.triangulation().vertex_triple_index(i,j));
        assert(mapping.find(w->point())!=mapping.end());
        out << mapping[w->point()] << " ";
      }
      out << std::endl;
      fi++;
    }
    
}

CGAL_END_NAMESPACE

#endif // CGAL_TRIANGULATION_PRINT_RAW_H //
// EOF //