CGAL users discussion list

[Andreas Fabri <>]

Hi Rahul,

its' explained here:


33.4   Basic Triangulations

33.4.1   Description

The class Triangulation_2<Traits,Tds> serves as a base class for the other 2D 
triangulations classes and implements the user interface to a triangulation.

The vertices and faces of the triangulations are accessed through handles, iterators and circulators. A handle is a model of the concept Handle which basically offers the 
two dereference operators * and -> . A circulator is a type devoted to visit circular sequences. Handles are used whenever the accessed element is not part of a sequence. 
Iterators and circulators are used to visit all or parts of the triangulation.

The iterators and circulators are all bidirectional and non mutable. The circulators and iterators are convertible to the handles with the same value type, so that when 
calling a member function, any handle type argument can be replaced by an iterator or a circulator with the same value type.

                    Source:  
http://www.cgal.org/Manual/beta/doc_html/cgal_manual/Triangulation_2/Chapter_main.html




The word "Handle" in the quote above leads here:
http://www.cgal.org/Manual/beta/doc_html/cgal_manual/Circulator_ref/Concept_Handle.html#Cross_link_anchor_1894

andreas



Rahul Kavalapara wrote:
> @Mathew Denno,
> Thanks, It worked.
>
> @ Andreas
> Thanks. It worked.
>
> "Triangle          t.triangle ( Face_handle f)    Returns the triangle 
> formed by the three vertices of f.
>                                                 Precondition:  The face 
> is finite.
>
> and all the face iterators and circulators are convertible to Face_handle."
>
>  From the above statement, did you mean face iterators and circulators 
> are implicitly converted to Face_Handle ?
> If I had to that explicitly, do I just type cast it ?
> I need to check the documentation and source code to deeply understand them.
>
>  
>
>
>
> --
> Rahul
>
>
> On Thu, Sep 10, 2009 at 1:11 PM, Andreas Fabri 
> < 
> <mailto:>> wrote:
>
>
>     Hi Rahul,
>
>     Remove the * befor fit.
>
>     The manual
>     
> http://www.cgal.org/Manual/beta/doc_html/cgal_manual/Triangulation_2_ref/Class_Triangulation_2.html#Cross_link_anchor_1235
>
>     says:
>
>     Triangle          t.triangle ( Face_handle f)    Returns the
>     triangle formed by the three vertices of f.
>                                                     Precondition:  The
>     face is finite.
>
>     and all the face iterators and circulators are convertible to
>     Face_handle.
>
>     best regards,
>
>     andreas
>
>
>
>     Rahul Kavalapara wrote:
>
>         Hi,
>
>         I am trying to output the vertices of triangles in a
>         Triangulation.  I tried to iterate over the faces using the
>         faces iterator, output the triangles vertices to std output.
>
>         
> ************************************************************************************
>
>         #include <fstream>
>         #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
>         #include <CGAL/Triangulation_2.h>
>         #include <CGAL/Triangle_2.h>
>
>         struct K : CGAL::Exact_predicates_inexact_constructions_kernel {};
>
>         typedef CGAL::Triangulation_2<K>         Triangulation;
>         typedef Triangulation::Vertex_circulator Vertex_circulator;
>         typedef Triangulation::Point             Point;
>         typedef Triangulation::Finite_faces_iterator Finite_faces_iterator;
>
>         int main()
>         {
>          std::ifstream in("triangulation_prog1.cin");
>          std::istream_iterator<Point> begin(in);
>          std::istream_iterator<Point> end;
>
>          Triangulation t;
>          t.insert(begin, end);
>
>          Finite_faces_iterator fit;
>          for(fit = t.finite_faces_begin(); fit != t.finite_faces_end();
>         ++fit)
>          {
>              K::Triangle_2 tri_2 = t.triangle(*fit);  <<-- Error
>              std::cout << tri_2 << "\n";
>          }
>          return 0;
>         }
>
>
>         Error:
>         triangulation_prog1.cpp: In function ‘int main()’:
>         triangulation_prog1.cpp:39: error: no matching function for call
>         to ‘CGAL::Triangulation_2<K, CGAL::Tds2<CGAL::Tvb<K,
>         CGAL::Tdsvb<void> >, CGAL::Tfb<K, CGAL::Tdsfb<void> > >
>          >::triangle(CGAL::Tfb<K, CGAL::Tdsfb<CGAL::Tds2<CGAL::Tvb<K,
>         CGAL::Tdsvb<void> >, CGAL::Tfb<K, CGAL::Tdsfb<void> > > > >&)’
>         /usr/include/CGAL/Triangulation_2.h:798: note: candidates are:
>         typename CGAL::Triangulation_2<Gt, Tds>::Triangle
>         CGAL::Triangulation_2<Gt, Tds>::triangle(typename
>         Tds::Face_handle) const [with Gt = K, Tds =
>         CGAL::Tds2<CGAL::Tvb<K, CGAL::Tdsvb<void> >, CGAL::Tfb<K,
>         CGAL::Tdsfb<void> > >]
>
>
>         Am I missing something for the above code.
>
>
>
>         --
>         Rahul
>
>
>     -- 
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