example_witness_complex_off.cpp

#include <sys/types.h>
#include <sys/stat.h>
 
#include <gudhi/Simplex_tree.h>
#include <gudhi/Euclidean_witness_complex.h>
#include <gudhi/pick_n_random_points.h>
#include <gudhi/choose_n_farthest_points.h>
#include <gudhi/Points_off_io.h>
 
#include <CGAL/Epick_d.h>
 
#include <iostream>
#include <fstream>
#include <ctime>
#include <string>
#include <vector>
 
using K = CGAL::Epick_d<CGAL::Dynamic_dimension_tag>;
using Point_d = K::Point_d;
using Witness_complex = Gudhi::witness_complex::Euclidean_witness_complex<K>;
using Point_vector = std::vector< Point_d >;
 
int main(int argc, char * const argv[]) {
  if (argc != 5) {
    std::cerr << "Usage: " << argv[0]
        << " path_to_point_file number_of_landmarks max_squared_alpha limit_dimension\n";
    return 0;
  }
 
  std::string file_name = argv[1];
  int nbL = atoi(argv[2]), lim_dim = atoi(argv[4]);
  double alpha2 = atof(argv[3]);
  clock_t start, end;
  Gudhi::Simplex_tree<> simplex_tree;
 
  // Read the point file
  Point_vector point_vector, landmarks;
  Gudhi::Points_off_reader<Point_d> off_reader(file_name);
  if (!off_reader.is_valid()) {
      std::cerr << "Witness complex - Unable to read file " << file_name << "\n";
      exit(-1);  // ----- >>
    }
  point_vector = Point_vector(off_reader.get_point_cloud());
 
  std::clog << "Successfully read " << point_vector.size() << " points.\n";
  std::clog << "Ambient dimension is " << point_vector[0].dimension() << ".\n";
 
  // Choose landmarks (decomment one of the following two lines)
  // Gudhi::subsampling::pick_n_random_points(point_vector, nbL, std::back_inserter(landmarks));
  Gudhi::subsampling::choose_n_farthest_points(K().squared_distance_d_object(), point_vector, nbL,
      Gudhi::subsampling::random_starting_point, std::back_inserter(landmarks));
 
  // Compute witness complex
  start = clock();
  Witness_complex witness_complex(landmarks,
                                  point_vector);
 
  witness_complex.create_complex(simplex_tree, alpha2, lim_dim);
  end = clock();
  std::clog << "Witness complex took "
      << static_cast<double>(end - start) / CLOCKS_PER_SEC << " s. \n";
  std::clog << "Number of simplices is: " << simplex_tree.num_simplices() << "\n";
}