CGAL users discussion list

[Stephane Tayeb <>]

Ramin H wrote:
> Thank you. That's right. There are exactly 35274 tetrahedra with subdomain
> index equal to 1.
>
> So what are the rest tetrahedra with a zero index for?

In a few words, the c3t3 (i.e. the output mesh) is a subset of the cells 
of the triangulation of all vertices which are inserted by the 
refinement process. Thus, some cells of this underlying triangulation 
are not part of the c3t3. When you put the object c3t3.triangulation() 
into a file, you save this complete underlying triangulation.

> I am trying to understand how exactly C3T3 works because I have issues with
> finding surface facets and their coherent normal vectors.

Maybe this could help you if you only have one subdomain. For each 
surface facet, can't you get the adjacent cell which is inside the 
domain and then orient the normal outward to this cell ?

> I appreciate your help.
> -Ramin
>
> On Thu, Apr 8, 2010 at 11:26 AM, Stephane Tayeb <
> >
>  wrote:
>
> > Ramin H wrote:
> >
> > > Hi,
> > > I save a c3t3 into out.mesh and it reports 35274 tetrahedra.
> > > I save the same c3t3 using "fileStream << c3t3.triangulation()" and the
> > > file
> > > shows 41444 cells.
> > >
> > > Why are these numbers inconsistent?
> > >
> > > -Ramin
> > > PS. The list does not allow me to attach the files (best compression size
> > > is
> > > 1440K). I can email it if needed.
> > Hi Ramin,
> >
> > The triangulation file contains all the tetrahedra of the triangulation,
> > whereas the .mesh file contains only the tetrahedra of the triangulation
> > which belong to the discretization of the input domain.
> >
> > This explains probably why your two numbers differ. Let me know if it's not
> > the case (you could for example check in the triangulation file how many
> > tetrahedra have a non-zero subdomain index).
> >
> > Stephane.
> >
> > --
> > Stephane Tayeb
> > Software engineer - INRIA Sophia Antipolis
> > Geometrica Project-Team
> >
> > --
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--
Stephane Tayeb
Software engineer - INRIA Sophia Antipolis
Geometrica Project-Team