CGAL users discussion list

["Mathieu Brédif" <>]

Hi,
the facet_begin() halfedge is arbitrary, your mistake is to assume
that facet2->facet_begin() is a particular halfedge handle.
My advice is to stay with halfedges without using the intermediate face 
handles:

A C = AB->prev()->opposite()
A'C = AC->next_on_vertex() // or more verbosely AB->next()->opposite()

Mathieu

On Wed, May 7, 2008 at 1:58 PM, samuel kim 
<>
 wrote:
> Hi all,
>
>  I am struggling in an implementation with the half edge data structure. 
> What I want to do is to travel the triangles from triangle# 1 to triangle# 
> 3 as shown at attached picture. For this, I read CGAL document and 
> implemented based on what I understood. But result is not going to 
> triangle# 3 but going back to triangle# 1 from triangle#2. The below is the 
> source code I tried.
>
>  Facet_handle hf_new;
>  Facet_iterator pFacet = facets_begin();
>  Halfedge_around_facet_circulator pHalfedge = pFacet->facet_begin(); // 
> expecting to get the handle of half_edge1 on triangle#1
>
>  hf_new = pHalfedge->prev()->opposite()->facet(); // expecting to get the 
> handle of facet of triangle#2
>  pHalfedge = hf_new->facet_begin(); // expecting to get the handle of 
> half_edge2 in the triangle#2
>
>  hf_new = pHalfedge->next()->opposite()->facet(); // expecting to get the 
> handle of facet of triangle#3
>  pHalfedge = hf_new->facet_begin(); // expecting to get the handle of 
> half_edge2 on the triangle#3
>
>
>  If I did as the above, the handle of facet was that of triangle#1. So I 
> want to ask you a question, when I do this,
>         hf_new = pHalfedge->prev()->opposite()->facet(); // expecting to 
> get the handle of facet of triangle#2
>         pHalfedge = hf_new->facet_begin(); // expecting to get the handle 
> of half_edge2 in the triangle#2
>  Which edge handle should be returned in triangle#2?
>  And what is the base rule to get to know the exact pointer of the handle 
> of half_edge data structure whenever travel triangles? Because I have tried 
> many times, and found that the pointer of handle of half_edge data 
> structure was varying at each triangle which was not expectable.
>
>  Thank you for your help.
>
>  Samuel
>
>
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