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[rcasero <>]

Hi Sebastien,

Thanks for your reply. Using an std::vector is a great idea. Although, I have been thinking about it, and given that std::vector allocates memory in a sequential block, it's not necessary to do a search.

As we get the memory address of the Triangle element, we can obtain the facet index subtracting the memory address of the first element. I have implemented it here

https://code.google.com/p/gerardus/source/browse/trunk/matlab/CgalToolbox/CgalClosestTriFacet.cpp?r=1128#236

The face index can be read doing

    // closest facet (facet indexes start at index 1)

    f[i] = &(*pp.second) - &(triangles[0]) + 1;

Thanks again for your help!

Best regards,

Ramon.

On 3 June 2013 12:30, Sebastien Loriot (GeometryFactory) [via cgal-discuss] <[hidden email]> wrote:

pp.second is an iterator in the container containing the triangles.

You can for example, change std::list<Triangle_3> to
std::vector<Triangle_3> and use std::distance(triangles.begin(),
pp.second) to get the index.

Sebastien.

On 06/01/2013 02:02 AM, rcasero wrote:

> Dear all,
>
> I have a triangulation and I'm trying to find the closest facet to a point
> using an AABB tree, but after much googling, and unsuccessfully trying to
> find the methods available to facets in the CGAL source code, I'd like to
> ask for a hand here.
>
> I tinkered with the code in the manual, "64.3.3   Tree of Polyhedron
> Triangle Facets for Distance Queries"
>
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/AABB_tree/Chapter_main.html#Subsection_64.3.3

>
> and "64.3.1   Tree of Triangles, for Intersection and Distance Queries"
>
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/AABB_tree/Chapter_main.html#Subsection_64.3.1
>

> I am able to compile and run the code, but what I've been unable to do is
> once I get to this
>
> Point_and_primitive_id pp = tree.closest_point_and_primitive(query);
> Primitive f = pp.second; // closest primitive id
>
> how to get an index to the facet (triangle) that is closest to the point.
> That is, if I have created my triangulation with something like this, using
> 10 triangles
>
> for  (int i = 0; i<  10; ++i) {
>    // read a triangle
>    x0 = ...
>    x1 = ...
>    x2 = ...
>
>    // add triangle to the list of triangles in the surface
>    triangles.push_back(Triangle(x0, x1, x2));
> }
>
> how I can tell from pp.second above which of the 10 triangles is the
> solution.
>
> Best regards,
>
> Ramon.
>
>
>
> --
> View this message in context: http://cgal-discuss.949826.n4.nabble.com/Getting-index-of-facet-closest-to-a-point-tp4657635.html

> Sent from the cgal-discuss mailing list archive at Nabble.com.
>

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--
Dr. Ramón Casero Cañas

Oxford e-Research Centre (OeRC)
University of Oxford
7 Keble Rd
Oxford OX1 3QG

tlf     +44 (0) 1865 610739
web     http://www.cs.ox.ac.uk/people/Ramon.CaseroCanas
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