Envelope_3/envelope_triangles.cpp

 
// Constructing the lower and the upper envelope of a set of triangles.
 
#include <iostream>
#include <list>
 
#include <CGAL/Exact_rational.h>
#include <CGAL/Cartesian.h>
#include <CGAL/Env_triangle_traits_3.h>
#include <CGAL/Env_surface_data_traits_3.h>
#include <CGAL/envelope_3.h>
 
using Number_type = CGAL::Exact_rational;
using Kernel = CGAL::Cartesian<Number_type>;
using Traits_3 = CGAL::Env_triangle_traits_3<Kernel>;
using Point_3 = Kernel::Point_3;
using Triangle_3 = Traits_3::Surface_3;
using Data_traits_3 = CGAL::Env_surface_data_traits_3<Traits_3, char>;
using Data_triangle_3 = Data_traits_3::Surface_3;
using Envelope_diagram_2 = CGAL::Envelope_diagram_2<Data_traits_3>;
 
/* Auxiliary function - print the features of the given envelope diagram. */
void print_diagram(const Envelope_diagram_2& diag) {
  // Go over all arrangement faces.
  for (auto fit = diag.faces_begin(); fit != diag.faces_end(); ++fit) {
    // Print the face boundary.
    if (fit->is_unbounded()) std::cout << "[Unbounded face]";
    else {
      // Print the vertices along the outer boundary of the face.
      auto ccb = fit->outer_ccb();
      std::cout << "[Face]  ";
      do std::cout << '(' << ccb->target()->point() << ")  ";
      while (++ccb != fit->outer_ccb());
    }
 
    // Print the labels of the triangles that induce the envelope on this face.
    std::cout << "-->  " << fit->number_of_surfaces() << " triangles:";
 
    for (auto sit = fit->surfaces_begin(); sit != fit->surfaces_end(); ++sit)
      std::cout << ' ' << sit->data();
    std::cout << std::endl;
  }
 
  // Go over all arrangement edges.
  Envelope_diagram_2::Edge_const_iterator eit;
 
  for (auto eit = diag.edges_begin(); eit != diag.edges_end(); ++eit) {
    // Print the labels of the triangles that induce the envelope on this edge.
    std::cout << "[Edge]  (" << eit->source()->point()
              << ") (" << eit->target()->point()
              << ") -->  " << eit->number_of_surfaces()
              << " triangles:";
 
    for (auto sit = eit->surfaces_begin(); sit != eit->surfaces_end(); ++sit)
      std::cout << ' ' << sit->data();
    std::cout << std::endl;
  }
}
 
/* The main program: */
int main() {
  // Construct the input triangles, makred A and B.
  std::list<Data_triangle_3> triangles;
  auto t1 = Triangle_3(Point_3 (0, 0, 0), Point_3 (0, 6, 0), Point_3 (5, 3, 4));
  triangles.push_back(Data_triangle_3(t1, 'A'));
  auto t2 = Triangle_3(Point_3 (6, 0, 0), Point_3 (6, 6, 0), Point_3 (1, 3, 4));
  triangles.push_back(Data_triangle_3(t2, 'B'));
 
  // Compute and print the minimization diagram.
  Envelope_diagram_2 min_diag;
  CGAL::lower_envelope_3(triangles.begin(), triangles.end(), min_diag);
  std::cout << std::endl << "The minimization diagram:" << std::endl;
  print_diagram(min_diag);
 
  // Compute and print the maximization diagram.
  Envelope_diagram_2 max_diag;
  CGAL::upper_envelope_3 (triangles.begin(), triangles.end(), max_diag);
  std::cout << std::endl << "The maximization diagram:" << std::endl;
  print_diagram (max_diag);
 
  return 0;
}