[vtkusers] Proving a surface mesh of closeness

[Marie-Gabrielle Vallet]

Dominik,
you're right. The check on non-manifold edges is just to detect some cases
that should not append.
Marie-Gabrielle

2008/10/9 Dominik Szczerba <dominik at itis.ethz.ch>

> I think for a simple (non-self-intersecting etc.) mesh it is enough for
> closedness if there are no boundary edges. No non-manifold edges proves
> topological correctness or 'simplicity', but is not required for
> closedness.
>
> Dominik
>
> On Thursday 09 October 2008 08:19:32 pm Marie-Gabrielle Vallet wrote:
> > For a surface mesh, in the vtkFeatureEdges terminology :
> >  - a boundary edge belongs to exactly one cell
> >  - a manifold edge belongs to two cells
> >  - a non-manifold edge belongs to 3 or more cells.
> > A simple close surface has only manifold edges.
> > BoundaryEdgesOn()
> > NonManifoldEdgesOn()
> > ManifoldEdgesOff()
> > FeatureEdgesOff()

> should return an empty set.
> >
> > A simple open surface has boundary edges and may has manifold too.
> > Having non-manifold edges means the surface intersects itself. It could
> > still be close, but I guess you don't want to deal with...
> >
> >
> > 2008/10/9 Dominik Szczerba <dominik at itis.ethz.ch>
> >
> > > Hmmm. Is a boundary edge of an open surface a non-manifold edge? It
> does
> > > not
> > > seem so, at least with the default settings.
> > >
> > > Dominik
> > >
> > > On Friday 03 October 2008 07:14:51 pm Marie-Gabrielle Vallet wrote:
> > > > I think there is a easier way of checking the surface closeness. I
> mean
> > > > using vtk facilities, instead of writing a (yet another) new
> algorithm.
> > > >
> > > > VTK library has algorithms to extract a mesh boundary, i.e. the set
> of
> > > > faces (in 3D) or edges (in 2D) that are not shared by two cells. See
> > > > vtkFeatureEdges. The mesh is close if and only if this set is empty.
> If
> > >
> > > it
> > >
> > > > not, you can visualize the holes that must still be closed.
> > > >
> > > > Pamela is trying to do the same thing today. Have a look at the
> thread
> > >
> > > "get
> > >
> > > > boundary triangles from a mesh" on this mailing list.
> > > >
> > > > By the way, Charles, are you sure you are not re-inventing the wheel
> ?
> > > >
> > > > Marie-Gabrielle
> > > >
> > > > >  Date: Fri, 3 Oct 2008 08:17:31 +0200
> > > > >  From: Dominik Szczerba <dominik at itis.ethz.ch>
> > > > >  Subject: Re: [vtkusers] Proving a surface mesh of closeness
> > > > >  To: vtkusers at vtk.org
> > > > >  Message-ID: <200810030817.31796.dominik at itis.ethz.ch>
> > > > >  Content-Type: text/plain;  charset="utf-8"
> > > > >
> > > > >  If it is manifold then pick the 1st element and make sure each one
> > > > > it has
> > > >
> > > > the
> > > >
> > > > >  proper number of neighbors (for triangles: 3). Mark the element as
> > > >
> > > > 'visited'
> > > >
> > > > >  and visit all his neighbors, repeating the procedure. At the end,
> if
> > > >
> > > > number
> > > >
> > > > >  of visited elements equals to number of elements in the mesh and
> all
> > > > > have their expected neighbors the mesh is closed.
> > > > >
> > > > >  DS
> > > > >
> > > > >  On Friday 03 October 2008 02:48:59 am Charles Monty Burns wrote:
> > > > >  > Hello,
> > > > >  >
> > > > >  > I repaired a surface mesh and want to prove whether the mesh is
> > > > >  > totally closed or not. Save is save ...
> > > > >  >
> > > > >  > How can I do this?
> > > > >  >
> > > > >  > Greetings
> > > > >
> > > > >  --
> > > > >  Dominik Szczerba, Ph.D.
> > > > >  Computational Physics Group
> > > > >  Foundation for Research on Information Technologies in Society
> > > > >  http://www.itis.ethz.ch <http://www.itis.ethz.ch/>
> > >
> > > --
> > > Dominik Szczerba, Ph.D.
> > > Computational Physics Group
> > > Foundation for Research on Information Technologies in Society
> > > http://www.itis.ethz.ch
>
>
>
> --
> Dominik Szczerba, Ph.D.
> Computational Physics Group
> Foundation for Research on Information Technologies in Society
> http://www.itis.ethz.ch
>
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