CGAL 5.3 - 3D Fast Intersection and Distance Computation (AABB Tree)
AABB_tree/AABB_custom_indexed_triangle_set_array_example.cpp
#include <iostream>
#include <boost/iterator/iterator_adaptor.hpp>
#include <CGAL/Simple_cartesian.h>
#include <CGAL/AABB_tree.h>
#include <CGAL/AABB_traits.h>
// The points are stored in a flat array of doubles
// The triangles are stored in a flat array of indices
// referring to an array of coordinates: three consecutive
// coordinates represent a point, and three consecutive
// indices represent a triangle.
typedef size_t* Point_index_iterator;
// Let us now define the iterator on triangles that the tree needs:
class Triangle_iterator
: public boost::iterator_adaptor<
Triangle_iterator // Derived
, Point_index_iterator // Base
, boost::use_default // Value
, boost::forward_traversal_tag // CategoryOrTraversal
>
{
public:
Triangle_iterator()
: Triangle_iterator::iterator_adaptor_() {}
explicit Triangle_iterator(Point_index_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;
// a static pointer to the vector containing the points
// is needed to build the triangles on the fly:
static const double* point_container;
private:
Id m_it; // this is what the AABB tree stores 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_index_iterator p_it = m_it.base();
Point p(*(point_container + 3 * (*p_it)),
*(point_container + 3 * (*p_it) + 1),
*(point_container + 3 * (*p_it) + 2) );
++p_it;
Point q(*(point_container + 3 * (*p_it)),
*(point_container + 3 * (*p_it) + 1),
*(point_container + 3 * (*p_it) + 2));
++p_it;
Point r(*(point_container + 3 * (*p_it)),
*(point_container + 3 * (*p_it) + 1),
*(point_container + 3 * (*p_it) + 2));
return Datum(p, q, r); // assembles triangle from three points
}
// one point which must be on the primitive
Point reference_point() const
{
return Point(*(point_container + 3 * (*m_it)),
*(point_container + 3 * (*m_it) + 1),
*(point_container + 3 * (*m_it) + 2));
}
};
// types
const double* My_triangle_primitive::point_container = nullptr;
int main()
{
// generates point set
double points[12];
My_triangle_primitive::point_container = points;
points[0] = 1.0; points[1] = 0.0; points[2] = 0.0;
points[3] = 0.0; points[4] = 1.0; points[5] = 0.0;
points[6] = 0.0; points[7] = 0.0; points[8] = 1.0;
points[9] = 0.0; points[10] = 0.0; points[11] = 0.0;
// generates indexed triangle set
size_t triangles[9];
triangles[0] = 0; triangles[1] = 1; triangles[2] = 2;
triangles[3] = 0; triangles[4] = 1; triangles[5] = 3;
triangles[6] = 0; triangles[7] = 3; triangles[8] = 2;
// constructs AABB tree
Tree tree(Triangle_iterator(triangles),
Triangle_iterator(triangles+9));
// counts #intersections
K::Ray_3 ray_query(K::Point_3(0.2, 0.2, 0.2), 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::cout << "closest point to " << point_query << " is: " << closest_point.x() << " " << closest_point.y() << " " << closest_point.z() << std::endl;
return EXIT_SUCCESS;
}