[vtkusers] how to bypass camera perspective transform

[francesco caruso]

Hello vtkusers

I've got a problem: I have to set a particular perspective
transform calculated by a process of camera calibration.
I can't set it with the methods SetClippingRange(), SetViewAngle() etc. 
because the aspect ratio is different than the viewport/window aspect 
ratio and because center of projection is not in the origin, so some 
elements that in the normal projection matrix are equal to 0 are 
different from 0.

I've tried a cheap solution without result :(  : apply to the actor
first my projection matrix (as if it was a modelview transformation) and 
then the inverse of the camera projection transformation obtained with 
GetActiveCamera()->GetProjectionMatrix( asp_ratio, near, far )

What's wrong in this?
How can I set my perspective projection?

Please Help me... Tomorrow I have to prepare a demo !!!

Regards
Francesco