[vtkusers] howto Prevent a dataobject from updating?

[John Biddiscombe]

I'm using a vtkImageData with no scalars or other data as an input to a 
probefilter.
This is nice because it's fast to set up and the "Points" are defined for 
me by setting origin/spacing and extents.
Problem is that after I setup the spacing/origin etc, the probefilter wants 
to call Update on the "input" even though its a fake input. Update does all 
sorts of ScalarAllocation and other guff which is wasted (it also dies when 
it tries to access the old scalar array to get the name)

How can I spoof the vtkImageData into thinking it doesn't need updating. 
(like setting modified time to before the last execute time of the 
probefilter...

thanks

JB