Seeding the mesh generator

mesh_with_my_seeding.cpp

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Mesh_triangulation_3.h>
#include <CGAL/Mesh_complex_3_in_triangulation_3.h>
#include <CGAL/Mesh_criteria_3.h>
#include <CGAL/Polyhedral_mesh_domain_3.h>
#include <CGAL/make_mesh_3.h>
#include <CGAL/refine_mesh_3.h>
#include <CGAL/grid_simplify_point_set.h>

// IO
#include <CGAL/IO/Polyhedron_iostream.h>

#include <boost/foreach.hpp>
#include <boost/lexical_cast.hpp>

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef K::Point_3 Point_3;

typedef CGAL::Polyhedron_3<K> Polyhedron;
typedef CGAL::Polyhedral_mesh_domain_3<Polyhedron, K> CGAL_Mesh_domain;


// My own domain class that basically overwrites the initialization

struct Mesh_domain : public CGAL_Mesh_domain {

  std::vector<Point_3> seeds;

  Mesh_domain(const Polyhedron& polyhedron, double cell_size)
    : CGAL_Mesh_domain(polyhedron),
      seeds(polyhedron.points_begin(), polyhedron.points_end())
  {
    // Select a subset of the points on the surface
    std::cerr << seeds.size() << " vertices" << std::endl;
    seeds.erase(CGAL::grid_simplify_point_set(seeds.begin(), seeds.end(), cell_size),
                seeds.end());
    
    std::cerr << seeds.size() << " seed points" << std::endl;
    
  }

  struct Construct_initial_points
  {
    Construct_initial_points(const std::vector<Point_3>& seeds)
      : seeds(seeds)
    {}

    template<class OutputIterator>
    OutputIterator operator()(OutputIterator pts, const int n = 8) const
    {
      BOOST_FOREACH(Point_3 p, seeds){
        *pts++ = std::make_pair(p,0);
      }
      return pts;
    }

  private:
    const std::vector<Point_3>& seeds;
  };

  Construct_initial_points construct_initial_points_object() const
  {
    return Construct_initial_points(seeds);
  }

};


// Triangulation
#ifdef CGAL_CONCURRENT_MESH_3
  typedef CGAL::Mesh_triangulation_3<
    Mesh_domain,
    CGAL::Kernel_traits<Mesh_domain>::Kernel, // Same as sequential
    CGAL::Parallel_tag                        // Tag to activate parallelism
  >::type Tr;
#else
  typedef CGAL::Mesh_triangulation_3<Mesh_domain>::type Tr;
#endif
typedef CGAL::Mesh_complex_3_in_triangulation_3<Tr> C3t3;

// Criteria
typedef CGAL::Mesh_criteria_3<Tr> Mesh_criteria;

// To avoid verbose function and named parameters call
using namespace CGAL::parameters;

int main(int argc, char*argv[])
{
  const char* fname = (argc>1)?argv[1]:"data/elephant.off";
  double cell_size = (argc>2)?boost::lexical_cast<double>(argv[2]) : 1.0;
  // Create input polyhedron
  Polyhedron polyhedron;
  std::ifstream input(fname);
  input >> polyhedron;
  if(input.bad()){
    std::cerr << "Error: Cannot read file " <<  fname << std::endl;
    return EXIT_FAILURE;
  }
  input.close();
 
  // Create domain
  Mesh_domain domain(polyhedron, cell_size);
  
  // Mesh criteria (no cell_size set)
  Mesh_criteria criteria(facet_angle=25, facet_size=0.15, facet_distance=0.008,
                         cell_radius_edge_ratio=3);
  
  // Mesh generation
  C3t3 c3t3 = CGAL::make_mesh_3<C3t3>(domain, criteria, no_perturb(), no_exude());

  // Output
  std::ofstream medit_file("out_1.mesh");
  c3t3.output_to_medit(medit_file);
  medit_file.close();

  return 0;
}