CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

sara Samadi wrote:
> Thanks for your help,
>  
> sorry, i cant understand the concept of "propagation from triangles to 
> triangles", is it possible for you to explain it little clearer?
>  

CGAL 2D triangulations are triangulations of the whole 2D plane (thanks 
to the infinite vertex).

A polygon in the 2D plane is defined by a close sequence of segments,
separating the triangles of the plane into two sets: those that are 
inside the polygon, and those that are outside the polygon.

Given a triangle, we can recover the whole set the triangle belongs to
by walking from triangle to triangle, never crossing a constrained edge.

As documented here:
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/TDS_2_ref/Concept_TriangulationDataStructure_2--Face.html

given a facet f, the three neighbor triangles can be retrieved using
f.neighbor(i) for i=0, 1 and 2.

S.


> Thanks in advance.
>
> --- On *Thu, 4/14/11, Sebastien Loriot (GeometryFactory) 
> /<>/* wrote:
>
>
>     From: Sebastien Loriot (GeometryFactory) 
> <>
>     Subject: Re: [cgal-discuss] Re: polygon triangulation
>     To: 
>
>     Date: Thursday, April 14, 2011, 6:59 AM
>
>     On 04/14/2011 05:32 AM, sara123 wrote:
>      > After reading the cgal manual (2D Triangulations) I realized that
>     after
>      > constrained triangulation of a simple polygon we have eventually
>     a convex
>      > polygon, even if our input polygon does'nt be convex!
>
>     Of course, it is computing a triangulation of the plane.
>     You have to filter out triangles that are outside you original polygon.
>
>     You can use a propagation from triangles to triangles, never crossing a
>     constrained edge. The simplest is to start with an infinite face and
>     get all faces that are not in the polygon.
>
>     S.
>
>
>
>      >
>      > what should i do if i want this does'nt happen?
>      >
>      >
>      > --
>      > View this message in context:
>     
> http://cgal-discuss.949826.n4.nabble.com/polygon-triangulation-tp3356157p3448688.html
>      > Sent from the cgal-discuss mailing list archive at Nabble.com.
>      >
>
>
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