NXT-Spy – Flag system

For the robot to recognize the drop zone (the place where it will drop the balls at), I thought about putting little flags 0n them with a black and white shape (to avoid any interference with the colored balls recognition).

My first idea was to work with 2D bar codes : a widely used open-source Java library called ZXing [source]. It can decode these two 2D bar code formats:

  • QR Code
  • Data Matrix

So I tried to encode the letter B and the letter R (for blue and red) in each of these formats.

QR code :

Data matrix:

So these are the most simple 2D code I could generate and I am not really happy of the size and complexity of those. Even the most simple of them (the data matrix) is generating an image of a complexity of 10×10.

So I am still trying to find a simpler 2D decodable symbol.

Supervisor’s comment:

Demonstrated that the QR matrix is probably the best solution because there are Java classes that detect it!
Arnaud was worried about size of flag relative to space balls working in.  I suggested a space of no more than 1.5m square, which will be feasible.  This will require quite large flags, a vertical phone perhaps lower down on the robot.
We also discussed his process architecture for ball recognition and robot control.  It has an implicit deadlock due to its network BUT he can argue that it will not deadlock by presenting the appropriate case and the order in which inputs to the processes happen.
As usual he is making really good progress; very well done
The task for next week is to see how well the system can detect QR codes, at what distance and size and orientation of flag.

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