CGAL users discussion list

[luchia <>]

Hallo,

I'm a new CGAL user and I'm facing a problem that actually I do not know how
to solve.

I'm writing the procedure Lower_hull that takes in input a Convex_hull_d
CH_d, an empty 
vector vfacet of type std::vector<Facet> with Facet of type
Convex_hull_d::Facet_handle             
and returns in vfacet the vector of all the facet of CH_d that belong to the
lower hull. 

Here is the code:

*void Lower_hull(Convex_hull_d& CH_d, VFacet vfacet) {
        Hyperplane hp;
        Vector_d normal;
        for (Facet_iterator i = CH_d.facets_begin(); i != CH_d.facets_end(); 
++i) {
                hp = CH_d.hyperplane_supporting(i); // Hyperplane of the i-th 
facet
                normal = hp.orthogonal_vector(); // Normal to hp
                if(normal[(normal.dimension())-1]<0)
                {
                        vfacet.push_back(i);
                        for (Convex_hull_d::Point_const_iterator j = 
i->points_begin(); j!=
i->points_end(); ++j){}
                }
        }
}*

Questions:

1. The idea to use the Hyperplane passing throuth a facet to extract its
orthogonal vector 
does it make sense?

2. Why the statement CH_d.hyperplane_supporting(i) is it correct? The method
hyperplane_supporting takes in input a facet_handle, while "i" its an
iterator over facet. Thus ... shouldn't we pass (*i) insteat of i?

3. The cicle:

for (Convex_hull_d::Point_const_iterator j = i->points_begin(); j!=
i->points_end(); ++j){}

was designed in order to iterate over the points of a given facet i. But it
does not work ... I obtained
a type error message.

Thaks your patience and for your help,

Luca






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