[vtkusers] Associating threshold rendinger with an interactor

[Vetria Byrd]

I am trying to write a program that will allow me to render vector field data.
I want to render the data using vtkThresholdPoints when the user presses a key 
then render the data using the vtkStreamLine when the user presses another key. 
How do I associate the threshold information with the interactor to setup 
callbacks?

Thanks,
Vetria