User Manual

Author

Ange Clément

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Definitions

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Examples

Feature Graph Extraction from a Segmented Image

The following example shows the extraction of the feature graph from a segmented image.

Example: Feature_graph/feature_graph_from_segmented_image.cpp

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// WARNING : non-functioning example. This exmaple is to understand how to create and use the feature graph for tetrahedral mesh creation.
 
#include <CGAL/Image_3.h>
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 
// Meshing definition
#include <CGAL/Mesh_triangulation_3.h>
#include <CGAL/Mesh_complex_3_in_triangulation_3.h>
#include <CGAL/Mesh_criteria_3.h>
 
#include <CGAL/make_mesh_3.h>
#include <CGAL/Image_3.h>
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Mesh_domain_with_polyline_features_3.h>
#include <CGAL/Labeled_mesh_domain_3.h>
 
// #include <CGAL/Mesh_3/polylines_to_protect.h>
#include <CGAL/boost/graph/split_graph_into_polylines.h>
#include <CGAL/Feature_graph/detect_sharp_features.h>

#ifdef CGAL_CONCURRENT_MESH_3
typedef CGAL::Parallel_tag Concurrency_tag;
#else
typedef CGAL::Sequential_tag Concurrency_tag;
#endif
 
typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Labeled_mesh_domain_3<K> Image_domain;
typedef CGAL::Mesh_domain_with_polyline_features_3<Image_domain> Mesh_domain;
 
typedef CGAL::Mesh_triangulation_3<Mesh_domain,CGAL::Default,Concurrency_tag>::type Tr;
typedef CGAL::Mesh_complex_3_in_triangulation_3<Tr> C3t3;
 
typedef CGAL::Mesh_criteria_3<Tr> Mesh_criteria;

typedef CGAL::Feature_graph::Detect_sharp_features_on_labeled_image<K> Feature_graph_detector;
 
// To avoid verbose function and named parameters call
namespace params = CGAL::parameters;
 
template<typename P, typename G>
struct Polyline_visitor
{
  std::vector<std::vector<P> >& polylines;
  G& graph;
  Polyline_visitor(typename std::vector<std::vector<P> >& lines, G& p_graph)
    : polylines(lines), graph(p_graph)
  {}
 
  void start_new_polyline()
  {
    std::vector<P> V;
    polylines.push_back(V);
  }
 
  void add_node(typename boost::graph_traits<G>::vertex_descriptor vd)
  {
    std::vector<P>& polyline = polylines.back();
    polyline.push_back(graph[vd]);
  }
 
  void end_polyline()
  {
    // ignore degenerated polylines
    if(polylines.back().size() < 2)
      polylines.resize(polylines.size() - 1);
  }
};
 
int main(int argc, char* argv[])
{
  const std::string fname = (argc>1)?argv[1]:CGAL::data_file_path("images/quadDomainCube.inr");

  CGAL::Image_3 image;
  if(!image.read(fname)){
    std::cerr << "Error: Cannot read file " <<  fname << std::endl;
    return EXIT_FAILURE;
  }

  Feature_graph_detector feature_graph_detector;
  const auto& feature_graph = feature_graph_detector(image);

  std::vector<std::vector<K::Point_3>> feature_graph_polylines;
  Polyline_visitor visitor(feature_graph_polylines, feature_graph);
  split_graph_into_polylines(feature_graph, visitor);
  Mesh_domain domain
    = Mesh_domain::create_labeled_image_mesh_domain(image,
         params::input_features = feature_graph_polylines);
 
  CGAL::Bbox_3 bbox = domain.bbox();
  double diag = CGAL::sqrt(CGAL::square(bbox.xmax() - bbox.xmin()) +
                           CGAL::square(bbox.ymax() - bbox.ymin()) +
                           CGAL::square(bbox.zmax() - bbox.zmin()));
  double sizing_default = diag * 0.05;

  Mesh_criteria criteria(params::edge_size = sizing_default,
    params::facet_angle = 30,
    params::facet_size = sizing_default,
    params::facet_distance = sizing_default / 10,
    params::cell_radius_edge_ratio = 0,
    params::cell_size = 0
  );

  C3t3 c3t3 = CGAL::make_mesh_3<C3t3>(domain, criteria,
                                      params::no_exude(),
                                      params::no_perturb());
 
  // Output
  CGAL::dump_c3t3(c3t3, "out");
 
  return 0;
}

Figure 90.1 Left: ...