CGAL users discussion list

[Monique Teillaud <>]

Kwok Jasper wrote:
> Hi.
>
>  From the CGAL manual about 3D triangulation, it said
>
> "Each cell gives access to its four incident vertices and to its four 
> adjacent cells. Each vertex gives direct access to one of its incident 
> cells, which is sufficient to retrieve all the incident cells when needed."
>
> "Edges (/1/-faces) and facets (/2/-faces) are not explicitly 
> represented: a facet is given by a cell and an index (the facet /i/ of a 
> cell /c/ is the facet of /c/ that is opposite to the vertex of index 
> /i/) and an edge is given by a cell and two indices (the edge /(i,j)/ of 
> a cell /c/ is the edge whose endpoints are the vertices of indices /i/ 
> and /j/ of /c/)."
>
> May I ask if it is possible to get a facet handle from a cell handle? 
> (i.e. the handle of the facet making up the cell)
>
>  From the CGAL manual, I can only find vertex handle from cell handle

Hi

The sentences of the manual that you copied above tell you that facets 
are not represented, so, there is no facet handle.

But in the reference manual of Triangulation_3, you can read:
typedef TriangulationDataStructure_3::Facet Facet;

and you have an html link to the manual of TriangulationDataStructure_3
where you can see:

typedef std::pair<Cell_handle, int>
        Facet;  (c,i) is the facet of c opposite to the vertex of index i.
which tells you how to access a facet.

        Monique Teillaud