[vtkusers] accessing a subvolume

[Steffen Oeltze]

Dear VTK-Gurus,

I have a 512³ volume stored in a vtkImageData. I would like to render just a
part of the volume. Is there a way to access only a subvolume of the 
vtkImageData, e.g. by using pointers ? I found vtkExtractVOI but this class 
creates a copy of the subvolume which would increase my memory demands.

Any help is appreciated,
Steffen Oeltze