CGAL users discussion list

[Manuel Caroli <>]

Hi Shi Yan and Jens,

just to clean up a bit:
There is the Triangulation_2 package that computes triangulations in 2d 
and so needs 2d points.
Then there is the Triangulation_3 package that normally computes 
triangulations in 3d (also called tetrahedralization). However, if you 
give the Triangulation_3 a set of points that all lie in one plane then 
this is considered a degenerate case and a two dimensional triangulation 
is computed. You can find in the manual how to extract it from the 
Triangulation_data_structure_3 then.

Note that it might be slower to compute a 2d Triangulation with the 
Triangulation_3 package than converting the points into a 2d coordiate 
system and use Triangulation_2.

Regarding the infinite vertex, there is always exactly one and it is 
adjacent to exactly all convex hull vertices.

best

Manuel


Shi Yan wrote:
> really? i thought the 3D triangulation is for tetrahedrons, not for
> triangles. i need definitely check the manual again.
>
> and i'm sorry, i don't quite understand what the infinite points are.
>
> thank you very much.
>
> On Thu, Oct 2, 2008 at 1:12 AM, Jens K. Becker 
> <>
>  wrote:
> > Hi Shi,
> >
> > I am not an expert with CGAL (yet), but I had the same problem. There are
> > plenty
> > of triangulation methods in 3D (all of them work in 3d if I am not
> > mistaken).
> > The resulting triangulation will be in 3D because infinite points will be
> > added
> > to your point set. If you just check for these points
> > (T.is_infinite(vertex))
> > and eliminating them should leave you with a triangulation in the plane.
> >
> > Greetings,
> >
> > Jens
> >
> > --
> > Dr. J.K. Becker
> > University of Tuebingen - Institute for Geoscience
> > Sigwartst. 10 - 72076 Tuebingen (Germany)
> > Tel.: ++49 7071 29 73139   Fax: +49 7071 5059
> > web: http://www.jkbecker.de
> >
> >
> > Quoting Shi Yan 
> > <>:
> >
> > > hello guys,
> > >
> > > i need to do triangulation inside a 3d triangle. the triangulation
> > > method provided by CGAL seems to be for 2D. so instead of me
> > > converting the 3D points into a 2D coordinate system, is there any
> > > convenient CGAL function that can do this for me?
> > >
> > > thank you very much.
> > > --
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