[vtkusers] how to pick a sub-volume from an image volume?

[kdsfinger at gmail.com]

hi, all
Suppose I have a 3D image stack and I can show its dimension as a cube
in vtk . Can I define another small sphere or cube such that I can
interactively place the small cube anywhere inside the imagedata, and
at the mean time, I can get the pixels inside the small sphere/cube?
Thanks for comments.
zl2k