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

CGAL 4.8 - 2D Arrangements

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Arrangement_on_surface_2/dcel_extension.cpp
// Extending all DCEL records (vertices, edges and faces).
#include <CGAL/Cartesian.h>
#include <CGAL/Exact_rational.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arrangement_2.h>
#include <CGAL/Arr_extended_dcel.h>
enum Color {BLUE, RED, WHITE};
typedef CGAL::Cartesian<CGAL::Exact_rational> Kernel;
typedef CGAL::Arr_segment_traits_2<Kernel> Traits_2;
typedef Traits_2::Point_2 Point_2;
typedef Traits_2::X_monotone_curve_2 Segment_2;
typedef CGAL::Arr_extended_dcel<Traits_2,Color, bool, int> Dcel;
typedef CGAL::Arrangement_2<Traits_2, Dcel> Arrangement_2;
int main ()
{
// Construct the arrangement containing two intersecting triangles.
Arrangement_2 arr;
Segment_2 s1 (Point_2(4, 1), Point_2(7, 6));
Segment_2 s2 (Point_2(1, 6), Point_2(7, 6));
Segment_2 s3 (Point_2(4, 1), Point_2(1, 6));
Segment_2 s4 (Point_2(1, 3), Point_2(7, 3));
Segment_2 s5 (Point_2(1, 3), Point_2(4, 8));
Segment_2 s6 (Point_2(4, 8), Point_2(7, 3));
insert_non_intersecting_curve (arr, s1);
insert_non_intersecting_curve (arr, s2);
insert_non_intersecting_curve (arr, s3);
insert (arr, s4);
insert (arr, s5);
insert (arr, s6);
// Go over all arrangement vertices and set their colors according to our
// coloring convention.
Arrangement_2::Vertex_iterator vit;
std::size_t degree;
for (vit = arr.vertices_begin(); vit != arr.vertices_end(); ++vit)
{
degree = vit->degree();
if (degree == 0)
vit->set_data (BLUE); // Isolated vertex.
else if (degree <= 2)
vit->set_data (RED); // Vertex represents an endpoint.
else
vit->set_data (WHITE); // Vertex represents an intersection point.
}
// Go over all arrangement edges and set their flags.
Arrangement_2::Edge_iterator eit;
bool flag;
for (eit = arr.edges_begin(); eit != arr.edges_end(); ++eit) {
// Check if the halfegde has the same diretion as its associated
// segment. Note that its twin always has an opposite direction.
flag = (eit->source()->point() == eit->curve().source());
eit->set_data (flag);
eit->twin()->set_data (!flag);
}
// For each arrangement face, print the outer boundary and its size.
Arrangement_2::Face_iterator fit;
Arrangement_2::Ccb_halfedge_circulator curr;
int boundary_size;
for (fit = arr.faces_begin(); fit != arr.faces_end(); ++fit) {
boundary_size = 0;
if (! fit->is_unbounded()) {
curr = fit->outer_ccb();
do {
++boundary_size;
++curr;
} while (curr != fit->outer_ccb());
}
fit->set_data (boundary_size);
}
// Copy the arrangement and print the vertices.
Arrangement_2 arr2 = arr;
std::cout << "The arrangement vertices:" << std::endl;
for (vit = arr2.vertices_begin(); vit != arr2.vertices_end(); ++vit) {
std::cout << '(' << vit->point() << ") - ";
switch (vit->data()) {
case BLUE : std::cout << "BLUE." << std::endl; break;
case RED : std::cout << "RED." << std::endl; break;
case WHITE : std::cout << "WHITE." << std::endl; break;
}
}
return 0;
}