[vtkusers] Probing Noraml to screen??

[D.M.P.Davies]

Help,

I've shelved this problem for a long time and just got back to it.

I want to probe results with a polygon set  which  is normal to the
screen- (similar to  a vtkFollower actor .).

What's the easiest way?? - Inverting (by some means) the viewing
transformation?? - Unpicking camera rolls/yaws etc??.

Has anyone out there done it??

Many Thanks.

Dave Davies