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Attempting to decouple the SCCharts Controller and physics calculations (amongst other things) from fixed pixel coordinates a world coordinate system was introduced. This coordinate system has its origin in the center between the two bottom flipper tips. Standing in front of the flipper the Y-axis points upwards on the playing field and the X-axis points to the right. One unit in the world coordinate system corresponds to 1m.

The main program relies on a (at compile-time present) transformation matrix definition which can be generated and tested with a small standalone tool. Testing requires recompilation of the tool. As there is no depth information available, points in the image that are in the same 2D position of an orthographic parallel view onto the playing field will be in different positions with the generated transformation, so this solution is certainly not exact.



make calibrate

This produces a binary file calibrate in the same directory.


1-4Choose the index of the point to set
tEnters a test mode, which prints clicked pixel coordinates in the world coordinate system via the configured transformation matrix in the console. This matrix must be present in the file calibration_config.h at compile time.
wGenerates and writes a transformation matrix from the four points (if all are present) into the file calibration_config.h 
qQuits the program

Reference Points

Point #Point in ImageDescription (when looking at flipper)Position in World Coordinates (Measured in meters)
1top rightTop of the left outlane detector wire-0.203, 0.106
2bottom rightHorizontal middle of the top edge of the black square on the tube shaped graphic-0.164, 0.685
3bottom leftBottom right corner of the letter 'E' trigger (right side of the ramp)0.199, 0.637
4top leftBottom of the right outlane detector wire0.200, 0.103

Calibration Points

The reference points used in the calibration (see table) were empirically corrected to the left, as the coordinate system resulting from the generated transformation was slightly shifted to the right. This may have been the case because it is hard to exactly match the reference points to pixels in the image. Subsequent calibrations may yield different errors in the coordinate system.

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