CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Nicholas Mario Wardhana wrote:
> On 13 January 2011 16:21, Sebastien Loriot (GeometryFactory)
> <>
>  wrote:
> > The Polyhedron_3 class of CGAL documented here:
> > http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Polyhedron_ref/Class_Polyhedron_3.html
> > provides iterator over vertices,facets and halfedges.
> >
> > Given a facet, you can use Halfedge_around_facet_const_circulator to get the
> > vertices of a face (using the incident vertex to each halfedge).
> >
> > See:
> > http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Polyhedron_ref/Class_Polyhedron_3-Traits---Facet.html
> >
> > I don't want to prevent you from implementing your own data structure if
> > you think it will be more efficient but you may save time by using an
> > existing one (in particular because many additional functionalities are
> > available in CGAL).
> >
> >
> > S.
>
> Hi Sebastien,
>
> Sorry for my late reply. I have been studying CGAL's polyhedron
> deeper, based on the link that you provided. Thank you for your
> suggestion two days ago. It turned out that using CGAL we can quickly
> have the polyhedron integrated to our code (reading documentation,
> wrapper implementation and basic testings only take two days).
>
> I have one question. Currently I use
> Polyhedron_incremental_builder_3<Halfedge> to build a polyhedron, and
> it is possible to access the vertices of a polyhedron by ID via
> Polyhedron_incremental_builder_3<Halfedge>::vertex(). I am just
> wondering whether there is a similar method to get a facet of a
> polyhedron by inputting the ID, as so far I haven't found such
> function. In the current implementation, I have to save every
> Facet_handle object returned by
> Polyhedron_incremental_builder_3<Halfedge>::begin_facet() in an
> external hash_map, with the IDs serving as the keys.
There is nothing to do it directly.
However, note that the Polyhedron has a template parameter to tune
the underlying HDS used.
The HDS can be either base on a lists (the default for Polyhedron) or on 
vectors. In the case of vectors, you have random access to facets 
container (using std::advance and facets_begin() for example).

The price you have to pay to use HDS based on vector is that you need to
have an upper bound on the number of vertices, facets and halfedges.

See:
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/HalfedgeDS_ref/Class_HalfedgeDS_list.html#Cross_link_anchor_1121
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/HalfedgeDS_ref/Class_HalfedgeDS_vector.html#Cross_link_anchor_1122


S.


> Thank you.
>
> Best regards,
> Nicholas Mario Wardhana