[vtkusers] Merging rectilinear grids

[Sam Yoffe]

Hello,

I am new to VTK and have just started using ParaView. I am having problems
merging two (or more) datafiles defined on a rectilinear grid. I searched
and didn't find a solution to my problem that worked, so I apologise if this
is a question that has been asked before.

To be specific, I have a code which manipulates a 64^3 lattice. This code is
parallel, and so with two cores working on it one of the dimensions is split
in half:
  process 0 has sites 0, 1, ..., 31 (= 32 sites) for the x-direction and 0,
..., 63 for y- and z-directions;
  process 1 has sites 32, ..., 63 (= 32 sites) for the x-direction and 0,
..., 63 for y- and z-directions.
Each process then outputs its data into VTK format (a vector defined at each
site). Note that there are no points in common between the two datasets.

I then load the two VTK files in ParaView. I want to be able to plot
streamlines in the full 64^3 volume, but if I start my tracers in one half
then the streamlines terminate as soon as they reach the boundary to the
other half. I used Group Datasets, but the resultant set exhibits the same
problem. I then used the merge filter, which also has the same problem:
streamlines terminate on the boundary to the other half (it also creates an
unstructured grid and memory usage shoots up).

The data always seems to be [0, ..., 31] [32, ..., 63] in two distinct
chunks, whereas I want to be able to work with the full [0, ..., 31, 32,
..., 63]. If I File > Save Data as a new VTK file, then when I load that
file it works fine and streamlines can meander as much as they want through
the entire volume, but the file is significant'y bigger than the original
two rectilinear datafiles (which I could stitch together myself, but I'd
like to avoid doing so).

Please could you let me know if it is possible to merge two (or more)
rectilinear datasets which do not overlap in such a way that streamlines can
be plotted through the whole volume. I can't seem to tell ParaView that the
two halves are connected together. I would like to avoid writing a shell
script (or similar) to merge the datafiles before loading into ParaView if
possible.

Many thanks in advance,
Sam
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