Partie interactive du site pédagogique ELECINF344/ELECINF381 de Télécom ParisTech (occurrence 2011).


Copterix: some reflexions about Kanade

After having spent hours focusing on our PID into the Télécom ParisTech’s dancing room, we joined Télécom Robotic’s room in order to work on our implementation of Lucas and Kanade algorithm, because of a giant chessboard in green and red, perfect for image processing. We fixed Copterix in the air using some strings, and started test, with or without threshold, and it wasn’t really efficient…
We thought a moment about using ‘unfisheye’ opencv’s algorithm (see joined photo to understand why we wanted to use it), but it took 0.6 seconds per frame on our Gumstix…


What our camera actually sees: we can observe a 'fisheye' effect

Then we stopped and decided we should decide exactly how, even if it worked, Lucas and Kanade would help us to correct Copterix’s drift.
As we have 10 frames per second when processing the algorithm, it will be really difficult to determine in real time if we actually corrected the drift whenever we would want to correct it, and that is why we imagined the following algorithm:

  1. wait for Copterix to be horizontal (pitch and yaw < epsilon)
  2. take a reference picture and search the good features to track on it (quite heavy operation)
  3. while Copterix is horizontal (pitch and yaw < epsilon)
  4. ____take a picture, compare it with reference
  5. ____if not horizontal (pitch and yaw >= epsilon)
  6. ______wait for Copterix to be horizontal (pitch and yaw < epsilon)
  7. ______go to 3.
  8. ____if drift is big enough (move size > threshold)
  9. ______go to 12.
  10. ____if we don’t find enough features to track
  11. ______go to 1.
  12. ask PID to incline Copterix toward the good direction (we have to decide an angle)
  13. wait a chosen time (we have to be over-precise on this data)
  14. ask PID to set Copterix horizontal
  15. go to 1.

The real difficulty of this algorithm is that it infers we do own a powerful and precise PID, able to remain horizontal most of the time, and to follow an order in the better and faster possible way, which is of course not true.

That is why we are now considering the fact that we may not have time to have a excellent PID AND implement such a precise algorithm; we will talk about it tomorrow with our teachers.

Sur le même sujet :

  1. Copterix: Lucas and Kanade
  2. Copterix: First flight
  3. Copterix: motors control, 1st test
  4. Copterix has had a harsh day
  5. Copterix : Topo sur Lucas and Kanade

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