\( \newcommand{\E}{\mathrm{E}} \) \( \newcommand{\A}{\mathrm{A}} \) \( \newcommand{\R}{\mathrm{R}} \) \( \newcommand{\N}{\mathrm{N}} \) \( \newcommand{\Q}{\mathrm{Q}} \) \( \newcommand{\Z}{\mathrm{Z}} \) \( \def\ccSum #1#2#3{ \sum_{#1}^{#2}{#3} } \def\ccProd #1#2#3{ \sum_{#1}^{#2}{#3} }\)

CGAL 4.8 - Point Set Processing

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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;
// Concurrency
#ifdef CGAL_LINKED_WITH_TBB
typedef CGAL::Parallel_tag Concurrency_tag;
#else
typedef CGAL::Sequential_tag Concurrency_tag;
#endif
int main(int argc, char*argv[])
{
const char* fname = (argc>1)?argv[1]:"data/sphere_1k.xyz";
// Reads a .xyz point set file in points[].
std::list<PointVectorPair> points;
std::ifstream stream(fname);
if (!stream ||
!CGAL::read_xyz_points(stream,
std::back_inserter(points),
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() 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<Concurrency_tag>(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;
}