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[AP <>]

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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