CGAL users discussion list

[Monique Teillaud <>]

well, I am not familiar with Alpha_shape_3, but at least I am afraid
there is no Face_handle in Triangulation_3...

Still, you can get the vertices of a facet, see the user and ref manual
of TriangulationDataStructure_3:
typedef std::pair<Cell_handle, int> Facet;      
(c,i) is the facet of c opposite to the vertex of index i.

So, f.first->vertex( (i+1)&3 ) gives the first vertex of facet f.
Same with (1+2) and (1+3) for the next two vertices.

        Monique Teillaud

Mariette Yvinec wrote:
> use fh->vertex(int i)
> where fh is a Face_handle.
> See the doc of Triangulation_3 and Trriangulation_data_structure_3
> 
> chen wenyu wrote:
> 
>> Hi,
>>
>> How can I get the vertex handle from a facet.
>>
>> Facet f = ....;
>>
>> // how to get the three vertex handles of this facet f
>>
>>
>> For example:
>>
>> -------------------------------------------------------
>>
>>// examples/Alpha_shapes_3/example_weight.C
>>
>>#include <CGAL/Exact_predicates_inexact_constructions_kernel 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Kernel_23_ref/Class_Exact_predicates_inexact_constructions_kernel.html#Cross_link_anchor_17>.h>
>>#include <CGAL/Weighted_alpha_shape_euclidean_traits_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Weighted_alpha_shape_euclidean_traits_3.html#Cross_link_anchor_804>.h>
>>#include <CGAL/Regular_triangulation_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_3_ref/Class_Regular_triangulation_3.html#Cross_link_anchor_762>.h>
>>#include <CGAL/Alpha_shape_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>.h>
>>#include <list>
>>
>>typedef CGAL::Exact_predicates_inexact_constructions_kernel 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Kernel_23_ref/Class_Exact_predicates_inexact_constructions_kernel.html#Cross_link_anchor_17>
>> K;
>>
>>typedef CGAL::Weighted_alpha_shape_euclidean_traits_3<K> 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Weighted_alpha_shape_euclidean_traits_3.html#Cross_link_anchor_804>
>> Gt;
>>
>>typedef CGAL::Alpha_shape_vertex_base_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_vertex_base_3.html#Cross_link_anchor_801><Gt>
>>         Vb;
>>typedef CGAL::Alpha_shape_cell_base_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_cell_base_3.html#Cross_link_anchor_800><Gt>
>>           Fb;
>>typedef CGAL::Triangulation_data_structure_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/TriangulationDS_3_ref/Class_Triangulation_data_structure_3.html#Cross_link_anchor_785><Vb,Fb>
>> Tds;
>>typedef CGAL::Regular_triangulation_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_3_ref/Class_Regular_triangulation_3.html#Cross_link_anchor_762><Gt,Tds>
>>       Triangulation_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_3_ref/Class_Triangulation_3.html#Cross_link_anchor_759>;
>>typedef CGAL::Alpha_shape_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799><Triangulation_3
>> 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_3_ref/Class_Triangulation_3.html#Cross_link_anchor_759>>
>>        Alpha_shape_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>;
>>
>>typedef Alpha_shape_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::Cell_handle
>>          Cell_handle;
>>typedef Alpha_shape_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::Vertex_handle
>>        Vertex_handle;
>>typedef Alpha_shape_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::Facet
>>                Facet;
>>typedef Alpha_shape_3 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::Edge
>>                 Edge;
>>typedef Gt::Weighted_point 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>
>>                  Weighted_point 
>><file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>;
>>typedef Gt::Bare_point                      Bare_point;
>>
>>int main()
>>{
>>  std::list<Weighted_point 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>>
>>  lwp;
>>
>>  //input : a small molecule
>>  lwp.push_back(Weighted_point 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>(Bare_point(
>>  1, -1, -1), 4));
>>  lwp.push_back(Weighted_point 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>(Bare_point(-1,
>>   1, -1), 4));
>>  lwp.push_back(Weighted_point 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>(Bare_point(-1,
>>  -1,  1), 4));
>>  lwp.push_back(Weighted_point 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>(Bare_point(
>>  1,  1,  1), 4));
>>  lwp.push_back(Weighted_point 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Triangulation_2_ref/Class_Weighted_point.html#Cross_link_anchor_750>(Bare_point(
>>  2,  2,  2), 1));
>>
>>  //build alpha_shape  in GENERAL 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_2_ref/Class_Alpha_shape_2.html#Enum_Mode>
>>  mode and set alpha=0
>>  Alpha_shape_3 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>
>>   as(lwp.begin(), lwp.end(), 0, Alpha_shape_3 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::GENERAL
>>  
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_2_ref/Class_Alpha_shape_2.html#Enum_Mode>);
>>
>>  //explore the 0-shape - It is dual to the boundary of the union.
>>  std::list<Cell_handle> cells;
>>  std::list<Facet>       facets;
>>  std::list<Edge>        edges;
>>  as.get_alpha_shape_cells(std::back_inserter(cells),
>>                         Alpha_shape_3 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::INTERIOR
>>  
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_2_ref/Class_Alpha_shape_2.html#Enum_Classification_type>);
>>  as.get_alpha_shape_facets(std::back_inserter(facets),
>>                          Alpha_shape_3 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::REGULAR
>>  
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_2_ref/Class_Alpha_shape_2.html#Enum_Classification_type>);
>>  as.get_alpha_shape_facets(std::back_inserter(facets),
>>                          Alpha_shape_3 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::SINGULAR
>>  
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_2_ref/Class_Alpha_shape_2.html#Enum_Classification_type>);
>>  as.get_alpha_shape_edges(std::back_inserter(edges),
>>                         Alpha_shape_3 
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_3_ref/Class_Alpha_shape_3.html#Cross_link_anchor_799>::SINGULAR
>>  
>> <file:///C:/Program%20Files/CGAL-3.2.1/doc_html/cgal_manual/Alpha_shapes_2_ref/Class_Alpha_shape_2.html#Enum_Classification_type>);
>>
>>//start here
>>
>> std::list<Facet>::iterator fbeg = facetr.begin();
>> std::list<Facet>::iterator fend = facetr.end(); 
>> 
>> for (int i = 0; fbeg != fend; fbeg++)
>> {
>>     Facet f = (Facet)fbeg;
>>
>>     ........................
>>
>>     // how to get the three vertex handles of this facet 
>> }
>>
>>}
>>  
>>
>>
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