Finding reference to the data actually being displayed after brushing ...

We're doing some really vanilla 2D and 3D scatter plots loading data into 
FlatField's for display.  We're also using SelectRangeWidget's for brushing the 
data.  Everything's working like a charm!  Our users are now asking to know 
after they finish brushing 1) how many points are left in the original data 
set, and 2) can they dump the currently displayed data to a new file now that 
they've filtered out all the unwanted stuff.  To take care of this, I need to 
find a reference to the "data" actually being displayed.  Following the data 
"trail" through the VisAD documentation, it's not clear to me where to find the 
"getXXX()" accessor to the actually displayed data set.

thanks...  dlf