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[quaternionboy <>]

Tried to manage parity but still get not consistent normals... Any ideas?

for (CGALTriangulation::Finite_facets_iterator it = T.finite_facets_begin();
        it != T.finite_facets_end();
        it++)
    {
        std::pair<CGALTriangulation::Cell_handle, int> f = *it;
        
        const Point& p0 = f.first->vertex((f.second))->point(); //not a
facet point, opposite
        const Point& p1 = f.first->vertex((f.second+1)&3)->point();
        const Point& p2 = f.first->vertex((f.second+2)&3)->point();
        const Point& p3 = f.first->vertex((f.second+3)&3)->point();
        
        //normals
        auto n = ( f.second % 2 == 1) ?
        CGAL::normal(p1, p2, p3) :
        CGAL::normal(p1, p3, p2);
        n = n/std::sqrt(n.squared_length());



teillaud wrote
> 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.
>>
> 
> 
> 
> 
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