Merge pull request #7801 from janetournois/Tet_remeshing-improve_doc-jtournois

Tetrahedral_remeshing - Doc improvements

Tetrahedral_remeshing/doc/Tetrahedral_remeshing/Tetrahedral_remeshing.txt

@@ -70,6 +70,10 @@ The only required parameter is a given target edge length that drives the remesh
 towards a high-quality tetrahedral mesh with improved dihedral angles, and a more
 uniform mesh, with edge lengths getting closer to the input parameter value.
 
+By default, the cells with a non-zero `Subdomain_index` are
+selected for remeshing. The cells with `Subdomain_index` equal to zero
+are ignored by the remeshing algorithm.
+
 \cgalExample{Tetrahedral_remeshing/tetrahedral_remeshing_example.cpp }
 
 
@@ -81,6 +85,10 @@ control on the remeshing process. In this example, a triangulation with two subd
 (defined by the `Subdomain_index` 2)
 of its subdomains is remeshed.
 
+Only the cells with a non-zero `Subdomain_index` will be remeshed.
+The named parameter `cell_is_selected_map` can be used to change this
+behavior.
+
 \cgalExample{Tetrahedral_remeshing/tetrahedral_remeshing_of_one_subdomain.cpp }
 
 

Tetrahedral_remeshing/examples/Tetrahedral_remeshing/tetrahedral_remeshing_example.cpp

@@ -19,7 +19,12 @@ int main(int argc, char* argv[])
   const std::size_t nbv = (argc > 2) ? atoi(argv[2]) : 1000;
 
   Remeshing_triangulation tr;
-  CGAL::Tetrahedral_remeshing::generate_input_one_subdomain(nbv, tr);
+  CGAL::Tetrahedral_remeshing::insert_random_points_in_cube(nbv, tr);
+
+  /// A subdomain index 0 is considered outside and is not remeshed
+  /// so we set finite cells to a non-zero `Subdomain_index`
+  for (auto cell : tr.finite_cell_handles())
+    cell->set_subdomain_index(1);
 
   CGAL::tetrahedral_isotropic_remeshing(tr, target_edge_length);
 

Tetrahedral_remeshing/examples/Tetrahedral_remeshing/tetrahedral_remeshing_generate_input.h

@@ -22,40 +22,9 @@ namespace CGAL
 namespace Tetrahedral_remeshing
 {
   template<typename Tr>
-  void generate_input_two_subdomains(const std::size_t& nbv, Tr& tr)
+  void insert_random_points_in_cube(const std::size_t& nbv, Tr& tr)
   {
     CGAL::Random rng;
-
-    typedef typename Tr::Point Point;
-    typedef typename Tr::Cell_handle Cell_handle;
-
-    while (tr.number_of_vertices() < nbv)
-      tr.insert(Point(rng.get_double(-1., 1.), rng.get_double(-1., 1.), rng.get_double(-1., 1.)));
-
-    using P = typename Tr::Geom_traits::Point_3;
-    const typename Tr::Geom_traits::Plane_3
-      plane(P(0, 0, 0), P(0, 1, 0), P(0, 0, 1));
-
-    for (Cell_handle c : tr.finite_cell_handles())
-    {
-      if (plane.has_on_positive_side(
-        CGAL::centroid(P(c->vertex(0)->point()),
-                       P(c->vertex(1)->point()),
-                       P(c->vertex(2)->point()),
-                       P(c->vertex(3)->point()))))
-        c->set_subdomain_index(1);
-      else
-        c->set_subdomain_index(2);
-    }
-    assert(tr.is_valid(true));
-  }
-
-
-  template<typename Tr>
-  void generate_input_one_subdomain(const std::size_t nbv, Tr& tr)
-  {
-    CGAL::Random rng;
-
     typedef typename Tr::Point Point;
     std::vector<Point> pts;
     while (pts.size() < nbv)
@@ -67,11 +36,23 @@ namespace Tetrahedral_remeshing
       pts.push_back(Point(x, y, z));
     }
     tr.insert(pts.begin(), pts.end());
+  }
 
-    for (typename Tr::Cell_handle c : tr.finite_cell_handles())
-      c->set_subdomain_index(1);
+  template<typename Plane, typename Tr>
+  void insert_points_on_plane(const Plane& plane, const std::size_t& nbv, Tr& tr)
+  {
+    CGAL::Random rng;
+    typedef typename Tr::Point Point;
+    std::vector<Point> pts;
+    while (pts.size() < nbv)
+    {
+      const double x = rng.get_double(-1., 1.);
+      const double y = rng.get_double(-1., 1.);
+      const double z = rng.get_double(-1., 1.);
 
-    assert(tr.is_valid(true));
+      pts.push_back(plane.projection(Point(x, y, z)));
+    }
+    tr.insert(pts.begin(), pts.end());
   }
 
   template<typename Tr>

Tetrahedral_remeshing/examples/Tetrahedral_remeshing/tetrahedral_remeshing_of_one_subdomain.cpp

@@ -5,29 +5,22 @@
 
 #include "tetrahedral_remeshing_generate_input.h"
 
-typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
-
-typedef CGAL::Tetrahedral_remeshing::Remeshing_triangulation_3<K> Remeshing_triangulation;
+using K = CGAL::Exact_predicates_inexact_constructions_kernel;
 
+using Remeshing_triangulation = CGAL::Tetrahedral_remeshing::Remeshing_triangulation_3<K>;
+using Subdomain_index = Remeshing_triangulation::Tds::Cell::Subdomain_index;
 
 template<typename Tr>
 struct Cells_of_subdomain_pmap
 {
-private:
-  using Cell_handle = typename Tr::Cell_handle;
-
   const int m_subdomain;
 
 public:
-  using key_type = Cell_handle;
+  using key_type = typename Tr::Cell_handle;
   using value_type = bool;
   using reference = bool;
   using category = boost::read_write_property_map_tag;
 
-  Cells_of_subdomain_pmap(const int& subdomain)
-    : m_subdomain(subdomain)
-  {}
-
   friend value_type get(const Cells_of_subdomain_pmap& map,
                         const key_type& c)
   {
@@ -41,17 +34,54 @@ public:
   }
 };
 
+Subdomain_index subdomain_on_side_of_plane(const K::Point_3& p,
+                                           const K::Plane_3& plane)
+{
+  if (plane.has_on_positive_side(p))
+    return 1;
+  else
+    return 2;
+}
+
+K::Point_3 centroid(const Remeshing_triangulation::Cell_handle c)
+{
+  return CGAL::centroid(c->vertex(0)->point(),
+                        c->vertex(1)->point(),
+                        c->vertex(2)->point(),
+                        c->vertex(3)->point());
+}
+
 int main(int argc, char* argv[])
 {
-  const double target_edge_length = (argc > 1) ? atof(argv[1]) : 0.1;
+  const double target_edge_length = (argc > 1) ? atof(argv[1]) : 0.05;
   const std::size_t nbv = (argc > 2) ? atoi(argv[2]) : 1000;
+  const std::size_t nbv_on_plane = (argc > 3) ? atoi(argv[3]) : 100;
 
+  /// Create a randomly generated triangulation of a sphere
   Remeshing_triangulation tr;
-  CGAL::Tetrahedral_remeshing::generate_input_two_subdomains(nbv, tr);
+  CGAL::Tetrahedral_remeshing::insert_random_points_in_cube(nbv, tr);
 
-  CGAL::tetrahedral_isotropic_remeshing(tr, target_edge_length,
+  /// Use vertical plane to split the mesh into two subdomains
+  const K::Plane_3 plane(0, 0, 1, 0);
+  CGAL::Tetrahedral_remeshing::insert_points_on_plane(plane, nbv_on_plane, tr);
+
+  /// A subdomain index 0 is considered outside and is not remeshed
+  /// so we set finite cells to a non-zero `Subdomain_index`
+  /// (depending on the side of the plane they are on)
+  for (auto cell : tr.finite_cell_handles())
+  {
+    const K::Point_3 cc = centroid(cell);
+    cell->set_subdomain_index(subdomain_on_side_of_plane(cc, plane));
+  }
+
+  /// Remesh only the cells of subdomain 2
+  CGAL::tetrahedral_isotropic_remeshing(tr,
+      target_edge_length,
       CGAL::parameters::cell_is_selected_map(
-        Cells_of_subdomain_pmap<Remeshing_triangulation>(2)));
+        Cells_of_subdomain_pmap<Remeshing_triangulation>{2}));
+
+  std::ofstream os("out.mesh");
+  CGAL::IO::write_MEDIT(os, tr);
 
   return EXIT_SUCCESS;
 }