[vtk-developers] Polyhedral challenge

Will Schroeder will.schroeder at kitware.com
Wed Mar 24 15:20:32 EDT 2010


David-

This is good timing. Hua has been looking into the problem too. We came up
with an initial, very limited solution and it will be good to have a more
thorough approach. We are looking forward to seeing what you did.

I'm curious, did you create a filter to do this? How did you implement it in
VTK....

Will

On Wed, Mar 24, 2010 at 2:39 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi Will,
>
> I've finally completed my code for clipping closed polydata shapes and
> creating new "cap" polygons so that the result is also a closed
> polydata.  The solution was more complicated than I originally
> thought.  After the branch I'll commit it to VTK.
>
>   David
>
>
> On Thu, Feb 18, 2010 at 2:57 PM, Will Schroeder
> <will.schroeder at kitware.com> wrote:
> > Awesome David, simply great. You are ahead of us for now, but we will
> > definitely need something like this soon. Can we ping you when we are
> ready?
> >
> > On Thu, Feb 18, 2010 at 3:04 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
> >>
> >> Hi Will,
> >>
> >> Have you and Hua done the "Clip" part of the cell implementation yet?
> >> If not, I might have some code that will help.  I've been working on a
> >> class for clipping of watertight polydata in VTK.  It does the capping
> >> of the open end after a clip:
> >>
> >> - contouring the polydata at the clip plane to get the clip-edges of
> >> the clipped polygons
> >> - joining the new edge line segments into a one or more cap polygons
> >> - identifying complex polygons, i.e. polygons with holes
> >> - triangulating the polygons (*partly done*)
> >>
> >> The "triangulating" part is the only part that I haven't finished
> >> (that's why I asked about Delaunay earlier).  I'm using ear-cut
> >> triangulation, which only works for simple polygons, but other than
> >> that everything is done.
> >>
> >>   David
> >>
> >>
> >> On Thu, Feb 18, 2010 at 9:38 AM, Will Schroeder
> >> <will.schroeder at kitware.com> wrote:
> >> > Hua and I have made progress on adding a vtkPolyhedron cell to VTK. We
> >> > have
> >> > a wiki page describing the tasks (which will take some time
> >> > to implement depending on our funding and
> >> > schedule http://www.vtk.org/Wiki/VTK/Polyhedron_Support). We are
> using
> >> > the
> >> > interpolation method of mean value coordinates which Hua has already
> >> > implemented, thus far it is a super algorithm. Comments are welcome.
> >> > We are now starting the integration into vtkUnstructuredGrid. If you
> are
> >> > interested let me know and at the appropriate point we can make our
> git
> >> > repository available.
> >> >
> >> >
> >> > On Thu, Jan 21, 2010 at 6:53 AM, Will Schroeder
> >> > <will.schroeder at kitware.com>
> >> > wrote:
> >> >>
> >> >> FYI-
> >> >>
> >> >> Hua Yang and I are adding a new cell type to VTK: the polyhedral
> cell.
> >> >> This is mainly to support our CFD friends who like to compute flow
> >> >> solutions
> >> >> using flux approaches (balance mass and energy in and out of a
> region).
> >> >>
> >> >> One of the key questions is how to interpolate across the interior of
> >> >> such
> >> >> a cell. In the past I have seen two typical approaches 1) tessellate
> >> >> the
> >> >> polyhedron into tetrahedra, and then use the tetrahedra to
> interpolate;
> >> >> and
> >> >> 2) use a 1/r**2 (or similar weighting function) to interpolate from
> the
> >> >> cell
> >> >> nodes to an interior point in the polyhedron. Both approaches have
> >> >> problems
> >> >> with continuity, etc.
> >> >>
> >> >> We are also researching other approaches. However in the interest of
> >> >> completeness, if anybody has suggestions for alternatives we'd love
> to
> >> >> hear
> >> >> about them.
> >> >>
> >> >> Will
> >> >
> >> >
> >> >
> >> > --
> >> > William J. Schroeder, PhD
> >> > Kitware, Inc.
> >> > 28 Corporate Drive
> >> > Clifton Park, NY 12065
> >> > will.schroeder at kitware.com
> >> > http://www.kitware.com
> >> > (518) 881-4902
> >> >
> >> > _______________________________________________
> >> > Powered by www.kitware.com
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> >> >
> >> >
> >> >
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> >>
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> >
> >
> >
> > --
> > William J. Schroeder, PhD
> > Kitware, Inc.
> > 28 Corporate Drive
> > Clifton Park, NY 12065
> > will.schroeder at kitware.com
> > http://www.kitware.com
> > (518) 881-4902
> >
>



-- 
William J. Schroeder, PhD
Kitware, Inc.
28 Corporate Drive
Clifton Park, NY 12065
will.schroeder at kitware.com
http://www.kitware.com
(518) 881-4902
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