CGAL users discussion list

[Andreas Fabri <>]

When the Polyhedron is empty this is a strong indication
that you have either more than 2 triangles adjacent to
the samew edge, or that your triangles are not oriented
consistently.   When you have a face    i,j,k,  then
a neighbor face is j, i, l   or i,l,j, or l,j,c,  that
is i and j must be oriented in different directions.

andreas

On 15/03/2012 10:36, Helmi Ben Hmida wrote:
> Hi Philipp,
> Thanks for u re replay,
> In fact, I want to write an off file onto a Polydehron. Unfortuantely,
> at the beganning, we don´t have theses OFF files, just we have a VRML
> and x3d file that we re converting to OFF files. We have made a forst
> attempt to convert the faces of the VRML to OFF, but, we re getting
> always an empty Polyhderon, based on Nicholas´s suggestions, it works
> with a triangulated faces, just with this compbination (see example). I
> tried to simulate others faces combination, but getting an empty
> Polyhderon.
> The question was, is there some specific restrictions, or algorithm to
> create theses faces.
>
> Hpepefully that it´s clear
>
> Thanks in advance for u re help, we r blocked here for 2 weeks
>
> Am 14.03.2012 23:40, schrieb Philipp Moeller:
> > Helmi Ben 
> > Hmida<>
> >  writes:
> >
> > > Hello every Body,
> > > I´m trying to weel create the edges in an OFF files respecting this
> > > template (functional example) in order to convert it to a
> > > polyderon. To do, an algorithm creating edges has to be automatically
> > > implemented.
> > > The standard example sent is this one
> > > OFF
> > > 8 10 0
> > > 19.454456 9.214429 9.195417
> > > 19.454456 9.214429 6
> > > 19.629456 9.214429 6
> > > 19.629456 9.214429 9.195417
> > > 19.629456 13.049429 6
> > > 19.629456 13.049429 8.724564
> > > 19.454456 13.049429 6
> > > 19.454456 13.049429 8.724564
> > > 3 0 1 2
> > > 3 2 3 0
> > > 3 3 2 4
> > > 3 4 5 3
> > > 3 5 4 6
> > > 3 6 7 5
> > > 3 7 6 1
> > > 3 1 0 7
> > > 3 3 5 7
> > > 3 7 0 3
> > > 3 7 0 3
> > >
> > >
> > > The problem is with the 4 last edges, is there any relations between
> > > them to be created automatically by an algorithm, since we have a
> > > verayty of 3D points number (not always 8)
> > >
> > > Thanks in advance
> > > H.
> > It's hard to understand what you want to do. Do you want to read or
> > write an OFF file from or into a Polyhedron? Polyhedron overloads
> > operator<< and operator>> for those tasks [1].
> >
> > If this has absolutely no relevance to your question, I misunderstood
> > you.
> >
> > HTH,
> > Philipp Moeller
> > GeometryFactory
> >
> > [1] :
> > http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Polyhedron/Chapter_main.html#Section_25.4


--
Andreas Fabri, PhD
Chief Officer, GeometryFactory
Editor, The CGAL Project

phone: +33.492.954.912    skype: andreas.fabri