CGAL users discussion list

["samuel kim" <>]

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

Attachment: travelingtriagnle.JPG
Description: JPEG image