[vtkusers] Need Help but No nobody gave me advice or answer : croping region on the volume rendered

[wassim_belhadj at topnet.tn]

Hi 

I'm starting with VTK and  I need the help that I have not found.
I posted the message three times but not always answers or advice.
is there experts who respond to messages that hanging time?
I hope that this time my problem will be solved.
I'am usiing VTK 5.0.2 for volume rendering from a CT Data sets. All works
good and i have a nice volume rendered.
I would like to allow user to set a croping region on the volume rendered
(for example when he presses a button a frame that can be manipulated in
width and height is added to the scene)
 
My questions are so :

1) How to set a croping region on the volume rendered?

2)How to apply change to the volume rendered ? ( render the  volume
selected).

3) Are there examples of this genre?


I hope  that you bring me help and I thank you in advance.

I'm stuck on this part then your advice will also be welcome