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["Sebastien Loriot (GeometryFactory)" <>]

For the incremental version in dimension 3, you should use the 
Delaunay_triangulation_3 to compute it (look at the dynamic example but 
do not call the conversion function to polyhedron).

Have a look at the file convex_hull_3_to_polyhedron_3.h to see how to 
get convex_hull facets from a triangulation (taking all cells incident
to the infinite vertex).

For the Convex_hull_d class, facets_begin returns a single-pass iterator
(I know, this is not documented).

Sebastien.


On 02/21/2012 07:20 PM, AP wrote:
> Dear all,
>
> I am currently implementing an algorithm that require an incremental
> computation of convex hull of points, and I need to know the normal to the
> facets of these convex hulls.
> The computation is done and updated without any problem following the demo
> example "incremental_hull_3_demo.cpp", but I have some strange problems in
> the exploration of the facets.
> Here is an example below.
>
> int main()
> {
>    Convex_hull_3 CH(3);  // create instance of the class with dimension == 3
>    /* Insertion of points in the convex hull
>       ... */
>      facet f,g; /* f and g should be used as iterator to explore the facets
> */
>      f = CH.facets_begin(); /* f should point on the first facet */
>      g = f; /* g point also on the first facet */
>      pl = CH.hyperplane_supporting(f);
>      std::cout<<  pl.a()<<  ","<<  pl.b()<<  ","<<  pl.c()<<  ","<<
> std::endl; /* We print the normal to the first facet */
>      f++; /* f is incremented and point on the second facet */
>      pl = CH.hyperplane_supporting(f);
>      std::cout<<  pl.a()<<  ","<<  pl.b()<<  ","<<  pl.c()<<  ","<<
> std::endl; /* We print the normal to the second facet */
>      pl = CH.hyperplane_supporting(g); /* g should be unchanged and should
> point on the first facet... */
>      std::cout<<  pl.a()<<  ","<<  pl.b()<<  ","<<  pl.c()<<  ","<<
> std::endl; /* And we should print the normal of the first facet, however...
> */
>      exit(0);
>      /* ... */
> }
>
> However, the printing on the screen is :
> 900060001,900060001,900060001,
> -898079935,-960032,-960032,
> -898079935,-960032,-960032,
> I.e. when we increment f, g is also incremented!!!
> This makes impossible to use a facet as "current" and the other as "next"
> the same way as we would with linked list in the language C. I have tried
> some tricks without beeing succesful. I have used a void * to store the
> adress pointed by g but it was refused by the compiler, and I have tried to
> use a const facet for g but its value was also changed!
>
> Thanks in advance for the help!
>
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> --
> View this message in context: 
> http://cgal-discuss.949826.n4.nabble.com/Exploration-of-facets-in-a-convex-hull-of-points-tp4407829p4407829.html
> Sent from the cgal-discuss mailing list archive at Nabble.com.