Get number of filtered spots

Hello everyone,
I want to retrieve the number of spots in a time series that are part of filtered trajectories. I use a Jython script to do so. Since I use a filter for the track length

filter2 = FeatureFilter('TRACK_DURATION', 0.84, True)

I thought I could simply use

model.getSpots().getNSpots(True)

to get this number. The spot collection is, however, not changed by this filter and I get the total number of spots, including those on shorter trajectories. How can I change that?

Thanks in advance!