Skeletonization: Add example

Author: afabri

Surface_mesh_skeletonization/doc/Surface_mesh_skeletonization/examples.txt

@@ -3,5 +3,6 @@
 \example Surface_mesh_skeletonization/MCF_Skeleton_example.cpp
 \example Surface_mesh_skeletonization/segmentation_example.cpp
 \example Surface_mesh_skeletonization/MCF_Skeleton_sm_example.cpp
+\example Surface_mesh_skeletonization/MCF_Skeleton_om_example.cpp
 \example Surface_mesh_skeletonization/simple_mcfskel_sm_example.cpp
 */

Surface_mesh_skeletonization/examples/Surface_mesh_skeletonization/CMakeLists.txt

@@ -9,6 +9,14 @@ find_package(CGAL REQUIRED)
 find_package(Eigen3 3.2.0) #(requires 3.2.0 or greater)
 include(CGAL_Eigen3_support)
 
+find_package(OpenMesh QUIET)
+
+if(OpenMesh_FOUND)
+  include(UseOpenMesh)
+else()
+  message(STATUS "Examples that use OpenMesh will not be compiled.")
+endif()
+
 if(TARGET CGAL::Eigen3_support)
   create_single_source_cgal_program("simple_mcfskel_example.cpp")
   create_single_source_cgal_program("simple_mcfskel_sm_example.cpp")
@@ -28,6 +36,11 @@ if(TARGET CGAL::Eigen3_support)
     segmentation_example)
     target_link_libraries(${target} PUBLIC CGAL::Eigen3_support)
   endforeach()
+
+  if(OpenMesh_FOUND)
+    create_single_source_cgal_program("MCF_Skeleton_om_example.cpp")
+    target_link_libraries( MCF_Skeleton_om_example PUBLIC CGAL::Eigen3_support PRIVATE ${OPENMESH_LIBRARIES})
+  endif()
 else()
   message(
     STATUS

Surface_mesh_skeletonization/examples/Surface_mesh_skeletonization/MCF_Skeleton_om_example.cpp

@@ -0,0 +1,81 @@
+
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <CGAL/Surface_mesh.h>
+#include <CGAL/Mean_curvature_flow_skeletonization.h>
+
+#include <OpenMesh/Core/IO/MeshIO.hh>
+#include <OpenMesh/Core/Mesh/PolyMesh_ArrayKernelT.hh>
+
+#include <CGAL/boost/graph/graph_traits_PolyMesh_ArrayKernelT.h>
+
+#include <fstream>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
+typedef Kernel::Point_3                                       Point;
+typedef OpenMesh::PolyMesh_ArrayKernelT</* MyTraits*/> Triangle_mesh;
+
+typedef boost::graph_traits<Triangle_mesh>::vertex_descriptor vertex_descriptor;
+
+typedef CGAL::Mean_curvature_flow_skeletonization<Triangle_mesh> Skeletonization;
+typedef Skeletonization::Skeleton                             Skeleton;
+
+typedef Skeleton::vertex_descriptor                           Skeleton_vertex;
+typedef Skeleton::edge_descriptor                             Skeleton_edge;
+
+int main(int argc, char* argv[])
+{
+  const std::string filename = (argc > 1) ? argv[1] : CGAL::data_file_path("meshes/elephant.off");
+
+  Triangle_mesh tmesh;
+  OpenMesh::IO::read_mesh(tmesh, filename);
+
+  if (!CGAL::is_triangle_mesh(tmesh))
+  {
+    std::cout << "Input geometry is not triangulated." << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  Skeleton skeleton;
+  Skeletonization mcs(tmesh);
+
+  // 1. Contract the mesh by mean curvature flow.
+  mcs.contract_geometry();
+
+  // 2. Collapse short edges and split bad triangles.
+  mcs.collapse_edges();
+  mcs.split_faces();
+
+  // 3. Fix degenerate vertices.
+  mcs.detect_degeneracies();
+
+  // Perform the above three steps in one iteration.
+  mcs.contract();
+
+  // Iteratively apply step 1 to 3 until convergence.
+  mcs.contract_until_convergence();
+
+  // Convert the contracted mesh into a curve skeleton and
+  // get the correspondent surface points
+  mcs.convert_to_skeleton(skeleton);
+
+  std::cout << "Number of vertices of the skeleton: " << boost::num_vertices(skeleton) << "\n";
+  std::cout << "Number of edges of the skeleton: " << boost::num_edges(skeleton) << "\n";
+
+  // Output all the edges of the skeleton.
+  std::ofstream output("skel-sm.polylines.txt");
+  for(Skeleton_edge e : CGAL::make_range(edges(skeleton)))
+  {
+    const Point& s = skeleton[source(e, skeleton)].point;
+    const Point& t = skeleton[target(e, skeleton)].point;
+    output << "2 "<< s << " " << t << "\n";
+  }
+  output.close();
+
+  // Output skeleton points and the corresponding surface points
+  output.open("correspondance-sm.polylines.txt");
+  for(Skeleton_vertex v : CGAL::make_range(vertices(skeleton)))
+    for(vertex_descriptor vd : skeleton[v].vertices)
+      output << "2 " << skeleton[v].point << "  " << get(CGAL::vertex_point, tmesh, vd)  << "\n";
+
+  return EXIT_SUCCESS;
+}