CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 08/13/2014 05:17 PM, Blaz Bratanic wrote:
> I am trying to implement a simple triangle intersection test (below),
> but i cant get it to work.
>
> I get a bad_get error
>
> terminate called after throwing an instance of
> 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::bad_get>
>  >'
>    what():  boost::bad_get: failed value get using boost::get
> Aborted
>
> when trying to extract Point from Intersection_and_primitive_id
> (boost::get<Point>(i1.first)). I guess i must
> be missing something.

The intersection might not always be a point.

Sebastien.

> Thanks in advance for any help.
>
> // Code snippet
>
> #include <iostream>
> #include <vector>
> #include <CGAL/Simple_cartesian.h>
> #include <CGAL/AABB_tree.h>
> #include <CGAL/AABB_traits.h>
> #include <CGAL/AABB_triangle_primitive.h>
>
> typedef CGAL::Simple_cartesian<double> K;
> typedef K::FT FT;
> typedef K::Ray_3 Ray;
> typedef K::Line_3 Line;
> typedef K::Point_3 Point;
> typedef K::Triangle_3 Triangle;
> typedef CGAL::Bbox_3 BoundingBox;
> typedef std::vector<Triangle>::iterator Iterator;
> typedef CGAL::AABB_triangle_primitive<K, Iterator> Primitive;
> typedef CGAL::AABB_traits<K, Primitive> AABB_triangle_traits;
> typedef CGAL::AABB_tree<AABB_triangle_traits> Tree;
>
> typedef Tree::Intersection_and_primitive_id<Triangle>::Type
>      Triangle_intersection;
> typedef Tree::Primitive_id Primitive_id;
>
> std::vector<bool> visible_triangles(std::vector<Triangle>& triangles,
>                                      size_t nrays_per_axis) {
>    // constructs AABB tree
>    Tree tree(triangles.begin(), triangles.end());
>    BoundingBox bbox = tree.bbox();
>
>    std::vector<bool> visibility(triangles.size(), false);
>
>    double x = bbox.xmin();
>    double y = bbox.ymin();
>    double dx = (bbox.xmax() - bbox.xmin()) / nrays_per_axis;
>    double dy = (bbox.ymax() - bbox.ymin()) / nrays_per_axis;
>
>    std::vector<Triangle_intersection> intersections;
>
>    for (int iy = 0; iy < nrays_per_axis; iy++, y += dy) {
>      for (int ix = 0; ix < nrays_per_axis; ix++, x += dx) {
>        Point a = {x, y, 1};
>        Point b = {x, y, 0};
>        Ray ray_query(a, b);
>
>        if (tree.do_intersect(ray_query)) {
>          intersections.clear();
>          tree.all_intersections(ray_query,
> std::back_inserter(intersections));
>
>          auto min_el =
>              std::min_element(intersections.begin(), intersections.end(),
>                               [&a](Triangle_intersection const& i1,
>                                    Triangle_intersection const& i2) {
>                return squared_distance(a, boost::get<Point>(i1.first)) <
>                       squared_distance(a, boost::get<Point>(i2.first));
>              });
>          visibility[std::distance(triangles.begin(), min_el->second)] =
> true;
>        }
>      }
>    }
>    return visibility;
> }
>
> int main() {
>    Point a(0.5, 0.0, 0.0);
>    Point b(0.0, 0.5, 0.0);
>    Point c(0.0, 0.0, 0.5);
>    Point d(0.0, 0.0, 0.0);
>    std::vector<Triangle> triangles = {Triangle(a, b, c), Triangle(a, b, d),
>                                       Triangle(a, d, c)};
>
>    auto visibility = visible_triangles(triangles, 10);
>
>    return 0;
> }