CGAL users discussion list

[Philipp Moeller <>]

rcasero 
<>
 writes:

> 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;

Which is what the call to std::distance does. Your version is probably
slower though. :)

>
>
> Thanks again for your help!
>
> Best regards,
>
> Ramon.
>
>
>
>
> On 3 June 2013 12:30, Sebastien Loriot (GeometryFactory) [via cgal-discuss]
> <>
>  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
> photos  http://www.flickr.com/photos/rcasero/
>
>
>
>
> --
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> http://cgal-discuss.949826.n4.nabble.com/Getting-index-of-facet-closest-to-a-point-tp4657635p4657648.html
> Sent from the cgal-discuss mailing list archive at Nabble.com.

-- 
Philipp Moeller 
GeometryFactory