[Paraview] VTK File Format Question

[Berk Geveci]

What you need is to volume render cell data instead of point data.
Unfortunately, ParaView does not support volume rendering of cell data in
images. However, it supports volume rendering of cell data in unstructured
grids. Try this:

- Create a STRUCTURED_POINTS with cell data
- Load it
- Apply Clean to Grid
- Volume render

I wouldn't recommend doing this if your volumes are going to become large.

-berk

On Mon, Dec 13, 2010 at 10:41 AM, Jeff Johnson <jj56 at indiana.edu> wrote:

> This is great, thanks Berk and Sebastien. Yes, I am trying to do volume
> rendering. My dataset represents a 3D grid occupancy map, where each cell
> has a specified likelihood of occupancy. I'd like to render that as a set of
> unit cells, where the opacity is directly related to the likelihood of
> occupancy (i.e., totally opaque means likelihood of 1, totally transparent
> mean likelihood of 0). Does that make sense?
>
> I did try STRUCTURED_POINTS for doing the volume rendering, and it's seems
> close to what I'm looking for, but maybe I'm not setting it up quite right:
> The coloring seems to radiate out from one side, and it also seems to bleed
> out into neighboring cells. If I could get the color to radiate from the
> center out (or just have the cell uniformly colored), and have the coloring
> end at the cell boundaries, that would be perfect. I've attached a pic of
> what I see.
>
> Thanks again, guys.
>
> -Jeff
>
>
>
>
> On Dec 13, 2010, at 07:22 , Berk Geveci wrote:
>
> > Assuming that you are defining a uniform rectilinear grid, you need
> STRUCTURED_POINTS. As for defining opacity, what is your goal? To do volume
> rendering? Other than when using volume rendering, opacity does not have any
> effect.
> >
> > If you need to define an arbitrary set of cubes, you probably need an
> unstructured grid.
> >
> > Can you give us an example of your dataset and visualization you want to
> do? A picture maybe?
> >
> > -berk
> >
> > On Sun, Dec 12, 2010 at 10:15 AM, Jeff Johnson <jj56 at indiana.edu> wrote:
> > Thanks, but I'm totally new to the VTK file format and ParaView, and the
> documentation is not clear. It seems like the STRUCTURED_GRID geometry is
> the proper one for what I need, but I can find virtually no examples of it's
> use. For instance, if I want to specify a set of unit cubes from a set of
> points, do I do that in POINT_DATA or CELL_DATA? If I want to color them and
> set an opacity, where does that information go? The documentation says that
> a lookup table is a set of RGBA values that is associated with scalar data,
> but what does the scalar data represent, and how do I associated it with the
> cubes?
> >
> > -Jeff
> >
> >
> > On Dec 12, 2010, at 03:27 , Sebastien Jourdain wrote:
> >
> > > Hi Jeff,
> > >
> > > on the help page of vtk (
> http://www.vtk.org/VTK/help/documentation.html)
> > > you do have a link on the VTK file format.
> > > You should be able to find all the informations that you need here:
> > > http://www.vtk.org/VTK/img/file-formats.pdf
> > >
> > > Seb
> > >
> > > On Sat, Dec 11, 2010 at 8:44 PM, Jeff Johnson <jj56 at indiana.edu>
> wrote:
> > >> Hi all,
> > >>
> > >> I'm using ParaView to visualize a dataset, and I'm trying to generate
> an ASCII VTK file that will specify a set of voxels, where each voxel has an
> associated color and opacity. Does anyone have any suggestions for how I
> should format the file? It seems like this should be easy, but I can't make
> heads or tails of the documentation.
> > >>
> > >> -Jeff
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