[vtkusers] Where can I find the correct use of the functions Modified() and Update()

[Jim Peterson]

All,
I am trying to understand the principles of the vtk Pipeline in relation 
to when and how to implement changes to data in the pipeline. What I 
have "discovered" so far is if I apply a transform of some kind to a set 
of points, if I use the Modified() function on that dataset, the changes 
will be visible the next time the data is rendered. I can see that the 
Modified() function updates the timestamp for the data object, and that 
value is used by the filters in the pipeline to determine whether there 
is a need to re-evaluate the data when the pipeline is updated. My 
question is when, if ever, would my program need to use the Update() 
method against one or more filters in a pipeline, and more important, 
could a misplaced Update() call revert modifications to an already 
updated data object? that is, could I transform some set of points, only 
to have them reverted by an Update()  call to a filter that results in 
replacing that data object as output? Can either Modified() or Update() 
be overused in an application that uses vtk?

I would be happy with any references to design patterns for vtk 
pipelines or references to illustrative examples.

Thanks in advance for any insight.