CGAL users discussion list

["Laurent Rineau (GeometryFactory)" <>]

Le vendredi 25 septembre 2009 19:05:47, Sybren A. Stüvel a écrit :
> Hi folks,
> 
> I'm building a Delaunay triangulation in 3D. After I added 29 points
> and stream the triangulation to a file I get the attached output. It
> contains the 29 points and 129 cells.
> 
> The first cell consists of vertices "15 0 5 19", so I assume vertex
> indices are 0 based. However, another cell consists of vertices "13 7
> 29 19". How can this be when there are only 29 points?
> 
> Can anyone shed some light on this? I've attached a rather minimal
> test program and its output. I compiled it on Ubuntu Linux using:
> 
> g++  -fno-gnu-keywords -pedantic -Wall -Weffc++ -Wextra -std=c++98 -g
> -lCGAL  basetest.cpp   -o basetest
> 
> but I saw the same problem on Windows XP with Visual C++ 2005 SP1.
> 
> I use CGAL 3.4.

Hi,

That is very nice that you attached your code. I have been repeating on this 
list how much that is important to get useful answers.

The file output of CGAL triangulation is not documented. It is not intended 
to 
be used by users. However, that is not really a secret either: the source 
code 
is published. The file output stores in the file all cells of the 
triangulation, 
even the infinite cells. The vertex #0 is probably the infinite vertex. If 
you 
only want the finite cells of the triangulation (that is, those that are 
inside 
the convex hull of the points), then just ignore the cells that have the 
vertex #0.

You can find an explanation about the infinite vertex and infinite cells in 
the 
manual, at the very beginning of the chapter about 3D triangulations:
http://www.cgal.org/Manual/last/doc_html/cgal_manual/Triangulation_3/Chapter_main.html

-- 
Laurent Rineau, PhD
Release Manager of the CGAL Project
http://www.cgal.org/
R&D Engineer at GeometryFactory
http://www.geometryfactory.com/