CGAL users discussion list

[Monique Teillaud <>]

Hi

see http://doc.cgal.org/latest/TDS_3/index.html#title0
and in particular a sentence in paragraph "Validity"
====
The set σ 4 of permutations of (0,1,2,3) has cardinality 24, and the set 
of positive permutations A4 has cardinality 12. Thus, for a given 
orientation, there are up to 12 different orderings of the four vertices 
of a cell.
Note that cyclic permutations are negative and so do not preserve the 
orientation of a cell.
====

whether vertices (i,i+1,i+2,i+3) (mod 4) are positively oriented depends 
on the parity of i

--
Monique Teillaud
http://www.inria.fr/sophia/members/Monique.Teillaud/
INRIA Sophia Antipolis - Méditerranée
Institut National de Recherche en Informatique et Automatique

Le 29/11/13 04:17, WChXiong a écrit :
> Hi, I'm new on CGAL.
> When I use CGAL::make_surface_mesh() to get surface mesh, I need to get
> consistency normals of every facets.Here my code:
>          for (C2t3::Facet_iterator face= c2t3.facets_begin(); face !=
> c2t3.facets_end(); ++face)
>         {
>                 C2t3::Cell_handle ch;
>                 ch = face->first;
>                 int index = face->second;
>                 Point pt0 = ch->vertex((index+1)&3)->point();
>                 Point pt1 = ch->vertex((index+2)&3)->point();
>                 Point pt2 = ch->vertex((index+3)&3)->point();
>
>                 Vector normals = CGAL::cross_product(pt1 - pt0, pt2- pt0);
>                 normals = normals / CGAL::sqrt(normals * normals );
>         }
> But the result is not correct. The normals is not consistent. The
> points(pt0, pt1, pt2) of face are not oriented ?? How I can get consistency
> normals of every facets. Thank you.
>
>
>
> --
> View this message in context: 
> http://cgal-discuss.949826.n4.nabble.com/How-I-get-the-right-normals-of-facet-tp4658491.html
> Sent from the cgal-discuss mailing list archive at Nabble.com.