CGAL users discussion list

["Laurent Rineau (GeometryFactory)" <>]

On vendredi 06 mai 2011 15:17:16 

 wrote:
> Hi,
> I computed the intersection points of a ray and a 3D object represented as
> a 3D complex (for example a tetrahedron mesh in 3D mesh generation).  I
> combined a 3D mesh generation procedure with an AABB tree. My query object
> is a line with fixed direction and crossing a vertex of the mesh (I
> consider parallel rays crossing each vertex for different intersection
> queries) and I use a kind of AABB_primitive, such as Datum is Triangle_3
> and Id is Tr::Facet_finite_iterator. Thus I can get back the triangulation
> facet from the intersected Object_and_primitive_id.

So far I understand what you did.

> My problem is that, for each line which crosses a vertex, I need to
> keep/control just the intersection point "before" this vertex.

What means "before"?

> I try to do
> this by defining this point for each vertex as the point lying in the
> facet opposite to the vertex (that is the index defining the facet
> coincides with the index of the vertex ).

Which facet? In a given cell incident to the vertex, one can speak about the 
opposite facet. But, in your context, what is the cell you consider? 

Because of what I have not understood so far, I have not understood the rest 
of the mail either...

What your are doing seems intersting, but you will have to explain more what 
you do.

Do you plan to share your code?

> I would expect to select in this
> way for each vertex just the two intersected facets opposite to the vertex
> and, sorting the two corresponding intersection points, to find the
> intersection point "before" the vertex. Conversely I detect a lot of
> intersections when applying this procedure. Is the adopted criterion
> wrong?
> Moreover I'm setting the condition c3t3.is_in_complex(cell) for the cell
> containing the intersected primitive to be assured of getting facets
> belonging the 3D complex. Does it correspond to get facets both inside the
> volume and on the surface or surface facets are excluded?
> 
> Thanks in advance for any suggestions!

-- 
Laurent Rineau, PhD
R&D Engineer at GeometryFactory           http://www.geometryfactory.com/
Release Manager of the CGAL Project       http://www.cgal.org/