Add an example for ray shooting

AABB_tree/doc/AABB_tree/aabb_tree.txt

@@ -137,6 +137,19 @@ a segment.  We finally compute the first intersection along a ray.
 
 \cgalExample{AABB_tree/AABB_polyhedron_facet_intersection_example.cpp}
 
+
+\subsection aabb_tree_examples_2 Ray Shooting
+
+In the following example we load a closed polyhedral surface and perform a
+ray shooting query from the centroid of each face, orthogonally to the face
+towards the interior.  As the centroid is computed with floating point
+arithmetic the first face hit by the ray may be the face of the centroid.
+The skip functor takes care of ignoring the face.
+
+\cgalExample{AABB_tree/AABB_ray_shooting_example.cpp}
+
+
+
 \subsection aabb_tree_examples_3 Tree of Polyhedron Triangle Facets for Distance Queries
 
 In the following example the AABB primitive wraps a facet handle of a

AABB_tree/doc/AABB_tree/examples.txt

@@ -8,6 +8,7 @@
 \example AABB_tree/AABB_polyhedron_facet_distance_example.cpp
 \example AABB_tree/AABB_polyhedron_facet_intersection_example.cpp
 \example AABB_tree/AABB_segment_3_example.cpp
+\example AABB_tree/AABB_ray_shooting_example.cpp
 \example AABB_tree/AABB_triangle_3_example.cpp
 \example AABB_tree/AABB_halfedge_graph_edge_example.cpp
 \example AABB_tree/AABB_face_graph_triangle_example.cpp

AABB_tree/examples/AABB_tree/AABB_polyhedron_facet_intersection_example.cpp

@@ -58,8 +58,10 @@ int main()
     if(intersection)
     {
         // gets intersection object
-      if(boost::get<Point>(&(intersection->first)))
+      const Point* p = boost::get<Point>(&(intersection->first))
-        std::cout << "intersection object is a point" << std::endl;
+      if(p)
+        std::cout << "intersection object is a point " << *p << std::endl;
+
     }
 
     // computes all intersections with segment query (as pairs object - primitive_id)
@@ -83,10 +85,6 @@ int main()
       if(boost::get<Segment>(&(plane_intersection->first)))
             std::cout << "intersection object is a segment" << std::endl;
     }
-
-    Point inside(0.1, 0.1, 0.1);
-    Ray ray(inside,r);
-    tree.first_intersection(ray);
     
     return EXIT_SUCCESS;
 }

AABB_tree/examples/AABB_tree/AABB_ray_shooting_example.cpp

@@ -0,0 +1,72 @@
+#include <iostream>
+#include <fstream>
+
+#include <CGAL/Simple_cartesian.h>
+#include <CGAL/AABB_tree.h>
+#include <CGAL/AABB_traits.h>
+#include <CGAL/Surface_mesh.h>
+#include <CGAL/AABB_face_graph_triangle_primitive.h>
+#include <CGAL/Polygon_mesh_processing/compute_normal.h>
+#include <CGAL/Polygon_mesh_processing/orientation.h>
+
+typedef CGAL::Simple_cartesian<double> K;
+typedef K::FT FT;
+typedef K::Point_3 Point;
+typedef K::Vector_3 Vector;
+typedef K::Ray_3 Ray;
+
+typedef CGAL::Surface_mesh<Point> Mesh;
+typedef boost::graph_traits<Mesh>::face_descriptor face_descriptor;
+typedef boost::graph_traits<Mesh>::halfedge_descriptor halfedge_descriptor;
+
+typedef CGAL::AABB_face_graph_triangle_primitive<Mesh> Primitive;
+typedef CGAL::AABB_traits<K, Primitive> Traits;
+typedef CGAL::AABB_tree<Traits> Tree;
+typedef boost::optional<Tree::Intersection_and_primitive_id<Ray>::Type> Ray_intersection;
+
+
+struct Skip {
+  face_descriptor fd;
+
+  Skip(const face_descriptor fd)
+    : fd(fd)
+  {}
+
+  bool operator()(const face_descriptor& t) const
+  { if(t == fd){
+      std::cerr << "ignore" << t  <<std::endl;
+    };
+    return(t == fd);
+  }
+  
+};
+
+int main(int argc, char* argv[])
+{
+  const char* filename = (argc > 1) ? argv[1] : "data/tetrahedron.off";
+  std::ifstream input(filename);
+  Mesh mesh;
+  input >> mesh;
+  Tree tree(faces(mesh).first, faces(mesh).second, mesh);
+  
+  double d = CGAL::Polygon_mesh_processing::is_outward_oriented(mesh)?-1:1;
+
+  BOOST_FOREACH(face_descriptor fd, faces(mesh)){
+    halfedge_descriptor hd = halfedge(fd,mesh);
+    Point p = CGAL::centroid(mesh.point(source(hd,mesh)),
+                             mesh.point(target(hd,mesh)),
+                             mesh.point(target(next(hd,mesh),mesh)));
+    Vector v = CGAL::Polygon_mesh_processing::compute_face_normal(fd,mesh);	
+    
+    Ray ray(p,d * v);
+    Ray_intersection intersection = tree.first_intersection(ray, Skip(fd));
+    if(intersection){
+      if(boost::get<Point>(&(intersection->first))){
+        const Point* p =  boost::get<Point>(&(intersection->first) );
+        std::cout <<  *p << std::endl;
+      }
+    }
+  }
+  std::cerr << "done" << std::endl;
+  return 0;
+}

AABB_tree/examples/AABB_tree/data/tetrahedron.off

@@ -0,0 +1,11 @@
+OFF
+4 4 0
+0.0 0.0 0.0
+1.0 0.0 0.0
+0.0 1.0 0.0
+0.0 0.0 1.0
+3 0 1 2
+3 0 3 1
+3 0 2 3
+3 1 3 2
+