Extract point for calcOpticalFlowPyrLK and cluster

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Hi!

I want to use calcOpticalFlowPyrLK to calculate optical flow inside some blob detected with Mog background subtractor. Due to the fact that LK optical flow is a sparse optical flow I have to give some points in input.

Reading on the net I have 3 possibility:

1. Use some lattice points, dividing blob regions in grid
2. Use goodFeatureToTrack
3. detect cornerns with cornerHarris

Which method is preferred? Are there some benchmark or comparison?

and then cluster them., wit - for example - kmeans. On what to cluster? Position of the point and optical flow intensity? Or what else?

Thanks in advance