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

CGAL 4.8 - 3D Fast Intersection and Distance Computation (AABB Tree)

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AABB_tree/AABB_custom_triangle_soup_example.cpp
// Author(s) : Camille Wormser, Pierre Alliez
// Example of an AABB tree used with a simple list of
// triangles (a triangle soup) stored into an array of points.
#include <iostream>
#include <vector>
#include <boost/iterator.hpp>
#include <CGAL/Simple_cartesian.h>
#include <CGAL/AABB_tree.h>
#include <CGAL/AABB_traits.h>
typedef CGAL::Simple_cartesian<double> K;
// My own point type
struct My_point {
double x;
double y;
double z;
My_point (double _x, double _y, double _z) : x(_x), y(_y), z(_z) {}
};
// The triangles are stored in a flat vector of points (a triangle soup):
// three consecutive points represent a triangle
typedef std::vector<My_point>::const_iterator Point_iterator;
// defines the iterator over triangles needed by the tree:
class Triangle_iterator
: public boost::iterator_adaptor<
Triangle_iterator // Derived
, Point_iterator // Base
, boost::use_default // Value
, boost::forward_traversal_tag // CategoryOrTraversal
>
{
public:
Triangle_iterator()
: Triangle_iterator::iterator_adaptor_() {}
explicit Triangle_iterator(Point_iterator p)
: Triangle_iterator::iterator_adaptor_(p) {}
private:
friend class boost::iterator_core_access;
void increment() { this->base_reference() += 3; }
};
// The following primitive provides the conversion facilities between
// my own triangle and point types and the CGAL ones
struct My_triangle_primitive {
public:
typedef Triangle_iterator Id;
// the CGAL types returned
typedef K::Point_3 Point;
typedef K::Triangle_3 Datum;
private:
Id m_it; // this is what the AABB tree will store internally
public:
My_triangle_primitive() {} // default constructor needed
// the following constructor is the one that receives the iterators from the
// iterator range given as input to the AABB_tree
My_triangle_primitive(Triangle_iterator a)
: m_it(a) {}
Id id() const { return m_it; }
// on the fly conversion from the internal data
// to the CGAL types
Datum datum() const
{
Point_iterator p_it = m_it.base();
Point p(p_it->x, p_it->y, p_it->z);
++p_it;
Point q(p_it->x, p_it->y, p_it->z);
++p_it;
Point r(p_it->x, p_it->y, p_it->z);
return Datum(p, q, r); // assembles a triangle from three points
}
// returns one point which must be on the primitive
Point reference_point() const
{
return Point(m_it->x, m_it->y, m_it->z);
}
};
// types
typedef CGAL::AABB_traits<K, My_triangle_primitive> My_AABB_traits;
typedef CGAL::AABB_tree<My_AABB_traits> Tree;
int main()
{
// generates triangle soup
My_point a(1.0, 0.0, 0.0);
My_point b(0.0, 1.0, 0.0);
My_point c(0.0, 0.0, 1.0);
My_point d(0.0, 0.0, 0.0);
std::vector<My_point> triangles;
triangles.push_back(a); triangles.push_back(b); triangles.push_back(c);
triangles.push_back(a); triangles.push_back(b); triangles.push_back(d);
triangles.push_back(a); triangles.push_back(d); triangles.push_back(c);
// constructs AABB tree
Tree tree(Triangle_iterator(triangles.begin()),
Triangle_iterator(triangles.end()));
// counts #intersections
K::Ray_3 ray_query(K::Point_3(1.0, 0.0, 0.0), K::Point_3(0.0, 1.0, 0.0));
std::cout << tree.number_of_intersected_primitives(ray_query)
<< " intersections(s) with ray query" << std::endl;
// computes closest point
K::Point_3 point_query(2.0, 2.0, 2.0);
K::Point_3 closest_point = tree.closest_point(point_query);
std::cerr << "closest point is: " << closest_point << std::endl;
return EXIT_SUCCESS;
}