[Paraview] Persistent data across time step changes in programmable filter

[Sean Ziegeler]

Howdy!  I'm writing a programmable filter that makes changes to a vector 
field based on grid point properties (it's a polar orthographic 
transform using a highly accurate Earth shape model).

This works well.  However, when one changes the time step, it recomputes 
those grid point properties to apply to the vector field.  This is a 
very expensive operation, and is quite unnecessary since the grid 
doesn't change over time.  I'd like to somehow cache the grid point 
property array so that I could simply reuse it if it's already been 
computed.

I thought about storing it as a Field Data array.  However, can one be 
guaranteed that the Field Data from the programmable filter *output* 
will still be in place within the same filter when the pipeline 
re-executes?  If not, is there some other mechanism for a programmable 
filter to retain persistent data across time step changes?

Thanks!
Sean