CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

If you really need the id, you need to look at the implementation in
include/CGAL/convex_hull_3_to_polyhedron_3.h and more precisely to the
operator(). The code is not hard to understand, you'll see that I
collect tetrahedra incident to the infinite vertex and extract vertices
that are on the convex hull and get correctly oriented facets too.

Sebastien.



horstmann wrote:
> Hello again Sebastien, and thak you so much for your valuable anwers, you are
> very kind and patient.
>
> Up to the moment, I have:
>
>  std::vector< std::pair<Point,unsigned> > points;
>   points.push_back( std::make_pair(Point(1,0,0),0) );
>   points.push_back( std::make_pair(Point(0,1,0),1) );
>   ..........
>   ..........
>   ..........
>
> // Create delaunay triangulation
>   Delaunay dt( points.begin(),points.end() );
>
>   // define polyhedron to hold convex hull
>   CGAL::Polyhedron_3<K> poly;
>
>   // Get only the surface
>   convex_hull_3_to_polyhedron_3(dt,poly);
>
> Or just:
>
>   // define polyhedron to hold convex hull
>   Polyhedron_3 poly;
>   
>   // compute convex hull of non-collinear points
>   CGAL::convex_hull_3(points.begin(), points.end(), poly);
>
> I think, both options perform the same, right? But with the second choice, I
> haven't be able to store the info together the points, so I choose the
> first.
>
> Now, I have to obtain what you already know, from the triangles that belong
> to the polyhedron, the 3 "id" vertices of each triangle (one triangle per
> line). The id, was stored as "info" together with each vertex.
>
> I suppose I have to iterate over the Facets, and for each Facet, iterate
> over its halfedges;
> doing that for example:
>
>  CGAL::Polyhedron_3<K>::Facet_iterator it;
>  CGAL::Polyhedron_3<K>::Facet::Halfedge_around_facet_circulator ci;
>
>   for (it = poly.facets_begin(); it != poly.facets_end(); it++)
>   {
>         ci = it->facet_begin();
>         ci->vertex()->point();
>
>         ci++;
>         ci->vertex()->point();
>
>         ci++;
>         ci->vertex()->point();
>
>   }
>
> This way, I have the 3 vertices of each triangle (ist x,y,z coordinates),
> but how can I recover the "id" I stored before as "info" ¿?
> I tried ci->vertex()->info(); , but it doesn't work.
>
> Do I lost the "info" I stored togethe with de Triangulation calling the
> function
>
>  ""convex_hull_3_to_polyhedron_3(dt,poly);"" 
>
> ?¿
>
> Thak you so much again.
>
>
>
> --
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> http://cgal-discuss.949826.n4.nabble.com/Help-getting-triangles-coordinates-from-Delaunay-Triangulation-tp3955310p4021298.html
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