[vtkusers] Cutting out a piece of a rectilinear grid

[tom fogal]

Hi all, I'm plotting streamlines using vtkStreamTracer from data in a
vtkRectilinearGrid, and having an issue concerning a convention used in
the dataset.

Within a certain radius from (0,0,0), the data aren't very good and I
would like to avoid tracing a stream line through it.
So I was wondering if there was any way to cut out a portion of a
rectilinear grid, or impose some sort of other artificial boundary on
the data?

Any ideas?

Thanks,

-tom