CGAL 6.2 - 2D Alpha Wrapping

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Alpha_wrap_2/point_set_wrap_2.cpp
#include "output_helper.h"
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/alpha_wrap_2.h>
#include <CGAL/Multipolygon_with_holes_2.h>
#include <CGAL/Point_set_3.h>
#include <CGAL/IO/read_points.h>
#include <CGAL/IO/WKT.h>
#include <CGAL/Real_timer.h>
#include <iostream>
#include <string>
using K = CGAL::Exact_predicates_inexact_constructions_kernel;
using Point_2 = K::Point_2;
using Point_3 = K::Point_3;
using Vector_2 = K::Vector_2;
using Vector_3 = K::Vector_3;
using Point_set_2 = CGAL::Point_set_3<Point_2, Vector_2>;
using Point_set_3 = CGAL::Point_set_3<Point_3, Vector_3>;
using Multipolygon = CGAL::Multipolygon_with_holes_2<K>;
int main(int argc, char** argv)
{
std::cout.precision(17);
std::cerr.precision(17);
const std::string filename = argc > 1 ? argv[1] : CGAL::data_file_path("points_3/circles.ply");
// This code reads a _3D_ point file
Point_set_3 point_set_3;
if(!CGAL::IO::read_points(filename,
point_set_3.index_back_inserter(),
CGAL::parameters::point_map(point_set_3.point_push_map())))
{
std::cerr << "Can't read input file " << filename << std::endl;
return EXIT_FAILURE;
}
// Project onto the xy plane
Point_set_2 point_set_2;
for (const auto& p3 : point_set_3.points())
point_set_2.insert(Point_2(p3.x(), p3.y()));
std::cout << point_set_2.size() << " points" << std::endl;
// Compute the alpha and offset values
const double relative_alpha = (argc > 2) ? std::stod(argv[2]) : 10.;
const double relative_offset = (argc > 3) ? std::stod(argv[3]) : 300.;
CGAL::Bbox_2 bbox;
for (const auto& p2 : point_set_2.points())
bbox += p2.bbox();
std::ofstream proj_out("projected.xyz");
proj_out.precision(std::numeric_limits<double>::max_digits10);
for (const auto& p2 : point_set_2.points())
proj_out << p2 << " 0\n";
proj_out.close();
const double diag_length = std::sqrt(CGAL::square(bbox.xmax() - bbox.xmin()) +
CGAL::square(bbox.ymax() - bbox.ymin()));
const double alpha = diag_length / relative_alpha;
const double offset = diag_length / relative_offset;
std::cout << "absolute alpha = " << alpha << " absolute offset = " << offset << std::endl;
// Construct the wrap
CGAL::Real_timer t;
t.start();
Multipolygon wrap;
CGAL::alpha_wrap_2(point_set_2.points(), alpha, offset, wrap);
t.stop();
std::cout << "Result: " << wrap.polygons_with_holes().size() << " polygon(s)" << std::endl;
std::cout << "Took " << t.time() << " s." << std::endl;
// Save the result
const std::string output_name = generate_output_name(filename, relative_alpha, relative_offset);
std::cout << "Writing to " << output_name << std::endl;
std::ofstream out(output_name);
out.precision(std::numeric_limits<double>::max_digits10);
CGAL::IO::write_multi_polygon_WKT(out, wrap);
std::cout << "Done." << std::endl;
return EXIT_SUCCESS;
}
CGAL::Bbox_2
CGAL::Bbox_2::ymax
double ymax() const
CGAL::Bbox_2::xmin
double xmin() const
CGAL::Bbox_2::ymin
double ymin() const
CGAL::Bbox_2::xmax
double xmax() const
CGAL::Exact_predicates_inexact_constructions_kernel
CGAL::Multipolygon_with_holes_2
CGAL::alpha_wrap_2
void alpha_wrap_2(const PointRange &points, const FaceRange &faces, const double alpha, const double offset, MultipolygonWithHoles &alpha_wrap, const InputNamedParameters &np=parameters::default_values())
computes a watertight, 1-manifold, simple multipolygon that strictly contains an input indexed face s...
Definition: alpha_wrap_2.h:166
CGAL::IO::read_points
bool read_points(const std::string &fname, PointOutputIterator output, const NamedParameters &np=parameters::default_values())
CGAL::square
NT square(const NT &x)
CGAL::IO::write_multi_polygon_WKT
std::ostream & write_multi_polygon_WKT(std::ostream &out, const MultiPolygon &polygons)