CGAL users discussion list

[Philipp Moeller <>]

tang 
<>
 writes:

> Dear Dr. Rineau and Loriot, 
>
> Could you please help me to take a look at it?
>
> The latest code is below, now I have the facet iterator i and the edge
> 'splitedge' to be splitted, the new point would be inserted into 'splitedge'
> is p, how to split the edge and facet?

The kind of manipulation you are after is not directly available in the
Polyhedron_3 [1] class. You will need to use the delegate member to
manipulate the underlying structure directly.

After that you need to work with the HDS [2]: create a new vertex, a new
pair of edges, and adjust all their pointers. You really should check
the validity of the HDS after that.

> Thanks,
> Zhanghong Tang
>
>
> PS: latest code
> void splitflattriangle(myobj *object,double edgelengthmin)
> {
>       /// this function is used to split small triangles height smaller 
> than the
> given threshold
>       /// a point will be inserted into one edge and the triangle will be
> splitted into two 
>       /// Zhanghong Tang @ 10/02/2012
>       Polyhedron *obj=(Polyhedron *)object->obj;
>       /// check for small area triangle
>       Point_3 p1, p2, p3, p;
>       Line_3 l;
>
>       double area, d12, d23, d31, dmax;
>       Facet_iterator i = obj->facets_begin();
>   for (  ; i != obj->facets_end(); ++i) 
>       {
>               /// get 3 points of this facet(triangle)
>               Halfedge_handle h = i->halfedge(), splitedge;
>               /// (p3->p1): h
>               /// (p1->p2): h->next()
>               /// (p2->p3): h->next()->next()
>     p1 = h->vertex()->point();
>     p2 = h->next()->vertex()->point();
>     p3 = h->next()->next()->vertex()->point();
>               Triangle_3 t(p1,p2,p3);
>               area=2.0*sqrt(CGAL::to_double(t.squared_area ())); 
>               d12=sqrt(CGAL::to_double(CGAL::squared_distance(p1,p2)));
>               if(d12<=edgelengthmin)continue;
>               d23=sqrt(CGAL::to_double(CGAL::squared_distance(p2,p3)));
>               if(d23<=edgelengthmin)continue;
>               d31=sqrt(CGAL::to_double(CGAL::squared_distance(p3,p1)));
>               if(d31<=edgelengthmin)continue;
>               dmax=max(max(d12, d23), d31);
>               if(area/dmax>edgelengthmin)continue;
>               /// get the projection of pi to longest edge
>               if(dmax==d12)
>               {
>                       l=Line_3(p1,p2);
>                       p=l.projection(p3);
>                       splitedge = h->next();  /// h->next() will be 
> splitted by p
>               }
>               else if(dmax==d23)
>               {
>                       l=Line_3(p2,p3);
>                       p=l.projection(p1);
>                       splitedge = h->next()->next();  /// h->next()->next() 
> will be splitted by
> p
>               }
>               else
>               {
>                       l=Line_3(p3,p1);
>                       p=l.projection(p2);
>                       splitedge = h;  /// h will be splitted by p
>               }
>       }
>       /// now I have the facet iterator i and the edge 'splitedge' to be
> splitted, 
>       /// the new point would be inserted into 'splitedge' is p, how to 
> split the
>       /// edge and facet?
>
>       /// after split the edge and facet, we reset the iterator to the 
> beginning
> of facet list
>       i = obj->facets_begin();
> }


Footnotes: 
[1]  
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Polyhedron_ref/Class_Polyhedron_3.html
[2]  
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/HalfedgeDS_ref/Chapter_intro.html