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

CGAL 4.8 - 2D Visibility

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Visibility_2/simple_polygon_visibility_2.cpp
#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Simple_polygon_visibility_2.h>
#include <CGAL/Arrangement_2.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arr_naive_point_location.h>
#include <istream>
#include <vector>
typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2 Point_2;
typedef Kernel::Segment_2 Segment_2;
typedef CGAL::Arr_segment_traits_2<Kernel> Traits_2;
typedef CGAL::Arrangement_2<Traits_2> Arrangement_2;
typedef Arrangement_2::Face_handle Face_handle;
typedef Arrangement_2::Edge_const_iterator Edge_const_iterator;
typedef Arrangement_2::Ccb_halfedge_circulator Ccb_halfedge_circulator;
int main() {
//create environment
Point_2 p1(0,4), p2(0,0), p3(3,2), p4(4,0), p5(4,4), p6(1,2);
std::vector<Segment_2> segments;
segments.push_back(Segment_2(p1, p2));
segments.push_back(Segment_2(p2, p3));
segments.push_back(Segment_2(p3, p4));
segments.push_back(Segment_2(p4, p5));
segments.push_back(Segment_2(p5, p6));
segments.push_back(Segment_2(p6, p1));
Arrangement_2 env;
CGAL::insert_non_intersecting_curves(env,segments.begin(),segments.end());
// find the face of the query point
// (usually you may know that by other means)
Point_2 q(0.5, 2);
Arrangement_2::Face_const_handle * face;
CGAL::Arr_naive_point_location<Arrangement_2> pl(env);
CGAL::Arr_point_location_result<Arrangement_2>::Type obj = pl.locate(q);
// The query point locates in the interior of a face
face = boost::get<Arrangement_2::Face_const_handle> (&obj);
// compute non regularized visibility area
// Define visibiliy object type that computes non-regularized visibility area
typedef CGAL::Simple_polygon_visibility_2<Arrangement_2, CGAL::Tag_false> NSPV;
Arrangement_2 non_regular_output;
NSPV non_regular_visibility(env);
non_regular_visibility.compute_visibility(q, *face, non_regular_output);
std::cout << "Non-regularized visibility region of q has "
<< non_regular_output.number_of_edges()
<< " edges:" << std::endl;
for (Edge_const_iterator eit = non_regular_output.edges_begin(); eit != non_regular_output.edges_end(); ++eit)
std::cout << "[" << eit->source()->point() << " -> " << eit->target()->point() << "]" << std::endl;
// compute non regularized visibility area
// Define visibiliy object type that computes regularized visibility area
typedef CGAL::Simple_polygon_visibility_2<Arrangement_2, CGAL::Tag_true> RSPV;
Arrangement_2 regular_output;
RSPV regular_visibility(env);
regular_visibility.compute_visibility(q, *face, regular_output);
std::cout << "Regularized visibility region of q has "
<< regular_output.number_of_edges()
<< " edges:" << std::endl;
for (Edge_const_iterator eit = regular_output.edges_begin(); eit != regular_output.edges_end(); ++eit)
std::cout << "[" << eit->source()->point() << " -> " << eit->target()->point() << "]" << std::endl;
return 0;
}