How did you collect your direction data? I would assume that you used compass direction, with North being 0, and following compass degrees. The problem with using radians, or Trig functions seems to be that the 0 in Radians is a compass 90, or East. Additionally Radians increase counter-clockwise as apposed to clockwise when using compass degrees. I am doing a similar task and I cannot figure out how to compensate for this offset. Did your points line up correctly?
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