Envelope_3/envelope_spheres.cpp

 
// Constructing the lower envelope of a set of spheres read from a file.
 
#include <CGAL/config.h>
 
#ifndef CGAL_USE_CORE
#include <iostream>
int main() {
  std::cout << "Sorry, this example needs CORE ..." << std::endl;
  return 0;
}
#else
 
#include <iostream>
#include <list>
#include <chrono>
 
#include <CGAL/Cartesian.h>
#include <CGAL/CORE_algebraic_number_traits.h>
#include <CGAL/Arr_conic_traits_2.h>
#include <CGAL/Env_sphere_traits_3.h>
#include <CGAL/envelope_3.h>
 
using Nt_traits = CGAL::CORE_algebraic_number_traits;
using Rational = Nt_traits::Rational;
using Algebraic = Nt_traits::Algebraic;
using Rat_kernel = CGAL::Cartesian<Rational>;
using Rat_point_3 = Rat_kernel::Point_3;
using Alg_kernel = CGAL::Cartesian<Algebraic>;
 
using Conic_traits_2 =
  CGAL::Arr_conic_traits_2<Rat_kernel, Alg_kernel, Nt_traits>;
 
using Traits_3 = CGAL::Env_sphere_traits_3<Conic_traits_2>;
using Sphere_3 = Traits_3::Surface_3;
using Envelope_diagram_2 = CGAL::Envelope_diagram_2<Traits_3>;
 
int main(int argc, char* argv[]) {
  // Get the name of the input file from the command line, or use the default
  // fan_grids.dat file if no command-line parameters are given.
  const char* filename = (argc > 1) ? argv[1] : "spheres.dat";
 
  // Open the input file.
  std::ifstream in_file(filename);
  if (! in_file.is_open()) {
    std::cerr << "Failed to open " << filename << " ..." << std::endl;
    return 1;
  }
 
  // Read the spheres from the file.
  // The input file format should be (all coordinate values are integers):
  // <n>                           // number of spheres.
  // <x_1> <y_1> <x_1> <R_1>       // center and squared radious of sphere #1.
  // <x_2> <y_2> <x_2> <R_2>       // center and squared radious of sphere #2.
  //   :     :     :     :
  // <x_n> <y_n> <x_n> <R_n>       // center and squared radious of sphere #n.
  int n = 0;
  std::list<Sphere_3> spheres;
  int x = 0, y = 0, z = 0, sqr_r = 0;
  in_file >> n;
  for (int i = 0; i < n; ++i) {
    in_file >> x >> y >> z >> sqr_r;
    spheres.push_back(Sphere_3(Rat_point_3(x, y, z), Rational(sqr_r)));
  }
  in_file.close();
  std::cout << "Constructing the lower envelope of " << n << " spheres.\n";
 
  // Compute the lower envelope.
  Envelope_diagram_2 min_diag;
  auto start = std::chrono::system_clock::now();
  CGAL::lower_envelope_3(spheres.begin(), spheres.end(), min_diag);
  std::chrono::duration<double> secs = std::chrono::system_clock::now() - start;
 
  // Print the dimensions of the minimization diagram.
  std::cout << "V = " << min_diag.number_of_vertices()
            << ", E = " << min_diag.number_of_edges()
            << ", F = " << min_diag.number_of_faces() << std::endl;
  std::cout << "Construction took " << secs.count() << " seconds.\n";
 
  return 0;
}
 
#endif