Point_set_processing_3/normals_example.cpp

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/pca_estimate_normals.h>
#include <CGAL/mst_orient_normals.h>
#include <CGAL/property_map.h>
#include <CGAL/IO/read_xyz_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;

int main(void)
{
    // Reads a .xyz point set file in points[].
    std::list<PointVectorPair> points;
    std::ifstream stream("data/sphere_20k.xyz");
    if (!stream ||
        !CGAL::read_xyz_points(stream,
                               std::back_inserter(points),
                               CGAL::First_of_pair_property_map<PointVectorPair>()))
    {
        std::cerr << "Error: cannot read file data/sphere_20k.xyz" << std::endl;
        return EXIT_FAILURE;
    }

    // Estimates normals direction.
    // Note: pca_estimate_normals() requires an iterator over points
    // as well as property maps to access each point's position and normal.
    const int nb_neighbors = 18; // K-nearest neighbors = 3 rings
    CGAL::pca_estimate_normals(points.begin(), points.end(),
                               CGAL::First_of_pair_property_map<PointVectorPair>(),
                               CGAL::Second_of_pair_property_map<PointVectorPair>(),
                               nb_neighbors);

    // Orients normals.
    // Note: mst_orient_normals() requires an iterator over 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.begin(), points.end(),
                                 CGAL::First_of_pair_property_map<PointVectorPair>(),
                                 CGAL::Second_of_pair_property_map<PointVectorPair>(),
                                 nb_neighbors);

    // 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;
}