[Paraview] D3 filter and PkdTrees: how to tell if D3 previously executed?, PkdTree point locators

[Christine Corbett Moran]

Hi,

I'm now playing around with creating some filters which use PkdTrees
internally, mainly for their point locator capabilities. As the
filters I'm interested in creating work best with spatial locality, I
want to execute D3 if running in parallel and it has not previously
been executed. I had four primary questions.

1. How do I tell if D3 has been executed previously in the pipeline?
2. It seems that I must first build a locator from points before
calling e.g. FindClosestNPoints even though D3 takes in the same data
set as input to build its KdTree. Does this mean
BuildLocatorFromPoints(input) builds a different sort (and, in turn,
new) KdTree than D3->SetInput(input) .... D3->Update()? Should I not
even bother trying to get the KdTree from D3 and simply create a new
one?
3. If I build my own PkDtree is this accomplished by creating a new
one on each process, and for my locator calling
BuildLocatorFromPoints(input) on each process, or should I do
something special on e.g. the root process?
4. If I run D3 and/or build a KdTree within my filter it would be nice
to save this for possible use by filters downstream. I see that D3 has
a SetRetainKdTree, which may be what I am looking for in that regard,
but if I build my own KdTree with associated locator is there a way to
retain it/access it downstream?

Christine