Point_set_processing_3/average_spacing_example.cpp

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/compute_average_spacing.h>
#include <CGAL/IO/read_xyz_points.h>

#include <vector>
#include <fstream>
#include <boost/tuple/tuple.hpp>

// Types
typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
typedef Kernel::FT FT;
typedef Kernel::Point_3 Point;

// Data type := index, followed by the point, followed by three integers that
// define the Red Green Blue color of the point.
typedef boost::tuple<int, Point, int, int, int> IndexedPointWithColorTuple;

int main(int argc, char*argv[])
{
    const char* fname = (argc>1)?argv[1]:"data/sphere_20k.xyz";
    // Reads a .xyz point set file in points.
    // As the point is the second element of the tuple (that is with index 1)
    // we use a property map that accesses the 1st element of the tuple.
    
    std::vector<IndexedPointWithColorTuple> points;
    std::ifstream stream(fname);
    if (!stream ||
        !CGAL::read_xyz_points(
            stream, std::back_inserter(points),
            CGAL::Nth_of_tuple_property_map<1,IndexedPointWithColorTuple>()))
    {
      std::cerr << "Error: cannot read file " << fname << std::endl;
      return EXIT_FAILURE;
    }

    // Initialize index and RGB color fields in tuple.
    // As the index and RGB color are respectively the first and third-fifth elements
    // of the tuple we use a get function from the property map that accesses the 0
    // and 2-4th elements of the tuple.
    for(unsigned int i = 0; i < points.size(); i++)
    {
      points[i].get<0>() = i;   // set index value of tuple to i

      points[i].get<2>() = 0;   // set RGB color to black
      points[i].get<3>() = 0;
      points[i].get<4>() = 0;
    }

    // Computes average spacing.
    const unsigned int nb_neighbors = 6; // 1 ring
    FT average_spacing = CGAL::compute_average_spacing(
                            points.begin(), points.end(),
                            CGAL::Nth_of_tuple_property_map<1,IndexedPointWithColorTuple>(),
                            nb_neighbors);
    std::cout << "Average spacing: " << average_spacing << std::endl;

    return EXIT_SUCCESS;
}