From the following:


In PiMotionAnalysis, "The data-type of the array is an (x, y, sad) structure where x and y are signed 1-byte values, and sad is an unsigned 2-byte value representing the sum of absolute differences of the block." What does x and y represent?

  • I believe it is the x and y value of the macro block (row and column) counting left and down from the top left. – Steve Robillard Nov 27 '15 at 4:37
  • Why signed then? And I do get positive and negative values. The example of PiMotionAnalysis uses the sqrt of the sum of squares of x and y. I'm puzzled because I would use only sad as the difference between each frame, why x and y before? What do they represent? I only have questions... – rmarques Nov 27 '15 at 7:57

I think I may have cracked it! Oh what good 3 hours of sleep do to us.

x and y may be the displacement vector of a given macroblock in his coordinate. I found this because when printing a['x'] and moving a sheet of paper along the camera x axis in one direction showed a matrix with mostly positive values and when moving to the other direction the signs changed.

I think I can work with this.

  • Oh dear! My apologies - I didn't write that piece of documentation very well - I'll revisit it before the next release! – Dave Jones Nov 27 '15 at 22:37
  • And just to confirm, yes it is indeed the vector displacement – Dave Jones Nov 27 '15 at 22:37
  • Thank you! I'm having a lot of fun swiping in front of the camera and getting commands executed while recording. It's amazing what the Pi is capable of. – rmarques Nov 28 '15 at 0:48
  • Have a look at these for some more ideas of playing with the analysis classes (I'm intending to get them into the docs for the next release when I get a spare second, but those are becoming extremely rare at the moment!) – Dave Jones Nov 28 '15 at 10:25
  • Will check them in detail this week, I'm very grateful. – rmarques Nov 29 '15 at 12:51

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