text: #include <cstdlib>
  #include <iostream>
  #include <fstream>
  #include <iterator>
  
  #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
  
  #include <CGAL/Random.h>
  
  #include <CGAL/Polyhedron_3.h>
  #include <CGAL/Polyhedron_items_with_id_3.h>
  #include <CGAL/IO/Polyhedron_iostream.h>
  
  #include <CGAL/Surface_mesh_shortest_path.h>
  #include <CGAL/boost/graph/graph_traits_Polyhedron_3.h>
  #include <CGAL/boost/graph/iterator.h>
  
  #include <boost/variant.hpp>
  
  typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
  typedef CGAL::Polyhedron_3<Kernel, CGAL::Polyhedron_items_with_id_3> Polyhedron_3;
  typedef CGAL::Surface_mesh_shortest_path_traits<Kernel, Polyhedron_3> Traits;
  typedef CGAL::Surface_mesh_shortest_path<Traits> Surface_mesh_shortest_path;
  typedef Traits::Barycentric_coordinate Barycentric_coordinate;
  typedef boost::graph_traits<Polyhedron_3> Graph_traits;
  typedef Graph_traits::vertex_iterator vertex_iterator;
  typedef Graph_traits::face_iterator face_iterator;
  typedef Graph_traits::vertex_descriptor vertex_descriptor;
  typedef Graph_traits::face_descriptor face_descriptor;
  typedef Graph_traits::halfedge_descriptor halfedge_descriptor;
  
  // A model of SurfaceMeshShortestPathVisitor storing simplicies
  // using boost::variant
  struct Sequence_collector
  {
    typedef boost::variant< vertex_descriptor,
                           std::pair<halfedge_descriptor,double>,
                           std::pair<face_descriptor, Barycentric_coordinate> > Simplex;
    std::vector< Simplex > sequence;
  
    void operator()(halfedge_descriptor he, double alpha)
    {
  
      sequence.push_back( std::make_pair(he, alpha) );
    }
  
    void operator()(vertex_descriptor v)
    {
      sequence.push_back( v );
    }
  
    void operator()(face_descriptor f, Barycentric_coordinate alpha)
    {
      sequence.push_back( std::make_pair(f, alpha) );
    }
  };
  
  // A visitor to print what a variant contains using boost::apply_visitor
  struct Print_visitor : public boost::static_visitor<> {
    int i;
    Polyhedron_3& g;
  
    Print_visitor(Polyhedron_3& g) :i(-1), g(g) {}
  
    void operator()(vertex_descriptor v)
    {
      std::cout << "#" << ++i << " : Vertex : " << get(boost::vertex_index, g)[v] << "\n";
    }
  
    void operator()(const std::pair<halfedge_descriptor,double>& h_a)
    {
      std::cout << "#" << ++i << " : Edge : " << get(CGAL::halfedge_index, g)[h_a.first] << " , ("
                                              << 1.0 - h_a.second << " , "
                                              << h_a.second << ")\n";
    }
  
    void operator()(const std::pair<face_descriptor, Barycentric_coordinate>& f_bc)
    {
      std::cout << "#" << ++i << " : Face : " << get(CGAL::face_index, g)[f_bc.first] << " , ("
                                              << f_bc.second[0] << " , "
                                              << f_bc.second[1] << " , "
                                              << f_bc.second[2] << ")\n";
    }
  };
  
  int main(int argc, char** argv)
  {
    // read input polyhedron
    Polyhedron_3 polyhedron;
    std::ifstream input((argc>1)?argv[1]:"data/elephant.off");
    input >> polyhedron;
    input.close();
  
    // initialize indices of vertices, halfedges and facets
    CGAL::set_halfedgeds_items_id(polyhedron);
  
    // pick up a random face
    const size_t randSeed = argc > 2 ? std::atoi(argv[2]) : 7915421;
    CGAL::Random rand(randSeed);
    const int target_face_index = rand.get_int(0, num_faces(polyhedron));
    face_iterator face_it = faces(polyhedron).first;
    std::advance(face_it,target_face_index);
    // ... and define a barycentric coordinate inside the face
    Barycentric_coordinate face_location = {{0.25, 0.5, 0.25}};
  
    // construct a shortest path query object and add a source point
    Surface_mesh_shortest_path shortest_paths(polyhedron);
    shortest_paths.add_source_point(*face_it, face_location);
  
    // pick a random target point inside a face
    face_it = faces(polyhedron).first;
    std::advance(face_it, rand.get_int(0, num_faces(polyhedron)));
  
    // collect the sequence of simplicies crossed by the shortest path
    Sequence_collector sequence_collector;
    shortest_paths.shortest_path_sequence_to_source_points(*face_it, face_location, sequence_collector);
  
    // print the sequence using the visitor pattern
    Print_visitor print_visitor(polyhedron);
    for (size_t i = 0; i < sequence_collector.sequence.size(); ++i)
      boost::apply_visitor(print_visitor, sequence_collector.sequence[i]);
  
    return 0;
  }
  