CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

This is most probably a floating point computation issue.

Also have a look here:
http://www.cgal.org/FAQ.html#inexact_NT

Sebastien.


On 11/10/2014 10:04 PM, Qingnan Zhou wrote:
> Dear all,
>
> There seems to be a bug that causes CGAL::AABBTree to produce wrong
> results.  The following code would illustrate the problem:
>
> It basically compute the center of each face and query the distance
> between the centroid and the mesh.  Ideally, the query should always
> return 0 as the distance and the source face index, otherwise the code
> will print out the face that causes the failure.
>
> typedef CGAL::Cartesian<Real> K;
> typedef K::Point_3 CGALPoint;
> typedef K::Triangle_3 CGALTriangle;
>
> typedef CGAL::AABB_tree<AABB_triangle_traits> AABBTree;
> typedef AABBTree::Point_and_primitive_id Point_and_primitive_id;
>
> ...
>
>      AABBTree *coarseTrianglesTree =
>          new AABBTree(triangles.begin(), triangles.end());
>      coarseTrianglesTree->accelerate_distance_queries();
>
>      size_t count = 0;
>      for (auto itr : triangles) {
>          CGALPoint c = CGAL::ORIGIN + ((
>          (itr[0] - CGAL::ORIGIN) +
>          (itr[1] - CGAL::ORIGIN) +
>          (itr[2] - CGAL::ORIGIN)) / 3.0);
>
>          Point_and_primitive_id pp =
> coarseTrianglesTree->closest_point_and_primitive(c);
>          size_t face_index = pp.second - triangles.begin();
>          double distance = coarseTrianglesTree->squared_distance(c);
>
>          if (distance > 1e-3) {
>              std::cout << count << std::endl;
>              std::cout << "distance  = " << distance << std::endl;
>              std::cout << "face idx  = " << face_index << std::endl;
>          }
>          count ++;
>      }
>
> When running this test on meshes such as "suzanne.obj
> <https://www.dropbox.com/s/j1xj8nfy68xpdqc/suzanne_tri.obj?dl=0>", the
> query fails on quite a few faces (the query finds the incorrect face
> index and gets a distance ~= 10^-3).
>
> We are able to reproduce the error with CGAL 4.4 and CGAL 4.5 on
>
> Redhat Enterprise Linux server with the following setting:
> gcc 4.8.2, gmp 6.0.0 (also tried 4.3.1), mpfr 3.1.2, boost 1.53
>
> CentOS 6.3 with the following setting:
> gcc 4.8.2, gmp 6.0.0a, mpfr 3.1.2, boost 1.55.0
>
> Strangely it works on the version compiled by macports.  We have tested
> CGAL 4.3 and 4.4 on mac.
>
> best,
> James