Point_set_processing_3/normals_example.cpp

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>

#include <CGAL/compute_average_spacing.h>
#include <CGAL/pca_estimate_normals.h>
#include <CGAL/mst_orient_normals.h>
#include <CGAL/property_map.h>
#include <CGAL/IO/read_points.h>

#include <utility> // defines std::pair
#include <list>
#include <fstream>

// Types
typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
typedef Kernel::Point_3 Point;
typedef Kernel::Vector_3 Vector;

// Point with normal vector stored in a std::pair.
typedef std::pair<Point, Vector> PointVectorPair;

// Concurrency
typedef CGAL::Parallel_if_available_tag Concurrency_tag;

int main(int argc, char*argv[])
{
  const char* fname = (argc>1) ? argv[1] : "data/sphere_1k.xyz";

  // Reads a point set file in points[].
  std::list<PointVectorPair> points;
  if(!CGAL::IO::read_points(fname,
                            std::back_inserter(points),
                            CGAL::parameters::point_map(CGAL::First_of_pair_property_map<PointVectorPair>())))
  {
    std::cerr << "Error: cannot read file " << fname<< std::endl;
    return EXIT_FAILURE;
  }

  // Estimates normals direction.
  // Note: pca_estimate_normals() requiresa range of points
  // as well as property maps to access each point's position and normal.
  const int nb_neighbors = 18; // K-nearest neighbors = 3 rings

  if (argc > 2 && std::strcmp(argv[2], "-r") == 0) // Use a fixed neighborhood radius
  {
    // First compute a spacing using the K parameter
    double spacing
        = CGAL::compute_average_spacing<Concurrency_tag>
          (points, nb_neighbors,
           CGAL::parameters::point_map(CGAL::First_of_pair_property_map<PointVectorPair>()));

    // Then, estimate normals with a fixed radius
    CGAL::pca_estimate_normals<Concurrency_tag>
        (points,
         0, // when using a neighborhood radius, K=0 means no limit on the number of neighbors returns
         CGAL::parameters::point_map(CGAL::First_of_pair_property_map<PointVectorPair>())
                          .normal_map(CGAL::Second_of_pair_property_map<PointVectorPair>())
                          .neighbor_radius(2. * spacing)); // use 2*spacing as neighborhood radius
  }
  else // Use a fixed number of neighbors
  {
    CGAL::pca_estimate_normals<Concurrency_tag>
        (points, nb_neighbors,
         CGAL::parameters::point_map(CGAL::First_of_pair_property_map<PointVectorPair>())
                          .normal_map(CGAL::Second_of_pair_property_map<PointVectorPair>()));
  }

  // Orients normals.
  // Note: mst_orient_normals() requires a range of points
  // as well as property maps to access each point's position and normal.
  std::list<PointVectorPair>::iterator unoriented_points_begin =
      CGAL::mst_orient_normals(points, nb_neighbors,
                               CGAL::parameters::point_map(CGAL::First_of_pair_property_map<PointVectorPair>())
                                                .normal_map(CGAL::Second_of_pair_property_map<PointVectorPair>()));

  // Optional: delete points with an unoriented normal
  // if you plan to call a reconstruction algorithm that expects oriented normals.
  points.erase(unoriented_points_begin, points.end());

  return EXIT_SUCCESS;
}