CGAL users discussion list

[Claus Volko <>]

I would like to remove faces from a polygon mesh. How can this be done?

Here is some code for you, which shows what I'm trying to do. In words, I try to remove faces that cannot be seen by the camera (the position of which is specified in camera_pos_x, camera_pos_y, camera_pos_z). These faces can be detected by computing the dot product of their vector to the camera and their normal vector. If it is close to zero, they are invisible and have to be removed.

  for (auto f : faces(polygon_mesh))

  {
      auto v0 = f->halfedge()->vertex()->point();
      auto v1 = f->halfedge()->next()->vertex()->point();
      auto v2 = f->halfedge()->next()->next()->vertex()->point();
      auto vmx = (v0.x() + v1.x() + v2.x()) / 3;
      auto vmy = (v0.y() + v1.y() + v2.y()) / 3;
      auto vmz = (v0.z() + v1.z() + v2.z()) / 3;
      auto w = f->plane().orthogonal_vector();
      auto wx = w.x() - camera_pos_x;
      auto wy = w.y() - camera_pos_y;
      auto wz = w.z() - camera_pos_z;
      auto w1 = new CGAL::Vector_3<Kernel>(wx, wy, wz);
      w1 = normalize(w1);
      auto res = w1->x() * vmx + w1->y() * vmy + w1->z() * vmz;
      if ((res > 0 && res < .75) || (res < 0 && res > -.75))

  }

Thank you in advance.

--

Dipl.-Ing. Dr. Claus D. Volko, BSc
http://www.cdvolko.net/