Use of Collections in Vtk...

[Terry J. Ligocki]

As a member of the Visualization Group at Lawrence Berkeley National
Laboratory, LBNL, I'm trying to use/extend Vtk to look at data sets that
are hierarchical collections of grid based data.

There are several capabilities I am in the process to providing for our
users.  The simplest is the option of resampling/flattening all the data
onto one grid and then using Vtk to visualize the single, resampled
grid.  This is just a basic capability we want available and this simply
requires adding a reader/resampler to Vtk.

The next capability we would like to have is the ability to pass these
collections of grids through a Vtk visualization pipeline as independent
objects which generate independent actors (or some type of collection or
assembly or actors) and are rendered simultaneously.

For example, imagine that you've define a pipeline that slices a grid
with an arbitrary plane, colors the result, and renders it.  Now, you'd
like to pass all the grids in a collection through this pipeline and see
the result.  Thus, you'd like to pass a collection of grids to a Vtk
visualization pipeline and see a collection of results rendered.

The question is:  How can this be done in Vtk?  I know that Vtk provides
"Collections" and "Assemblies" but it doesn't appear that the Vtk
objects/methods have been extended to iterate over input Collections and
generate output Collections.  If this were the case then a Collection of
grids could be fed into a Vtk pipeline and the resulting Collection (or
Assembly?) of actors could be rendered.

Do any capabilities currently exist in Vtk that would help support this
(beyond the existence of Collections and Assemblies)?  Is this
capability available in Vtk as it stands (i.e. have I missed something
(which is quite possible!))?  This capabilities would be useful anytime
there was a collection of objects that you wanted to visualize
simultaneously in the same way.  In all these cases, the number of
grid/objects is not fixed from data set to data set and may vary as
different subsets are selected within a data set (e.g. all grids at a
given resolution, all grids within a certain volume).

Finally, we are looking at ways of extending visualization algorithms to
treat these collections of grids as non-independent data (e.g.
understand hierarchies and data overlap).  This is something that
depends on the details of the data and its representation at we will be
adding them as custom extensions to Vtk.

So, the main questions I have is about using/extending Vtk with
Collections of grids (and/or other data).  Thank you in advance for any
help, thoughts, advice, or information...

				Terry J. (Ligocki, tjligocki at lbl.gov)


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