What is the easiest way to find the difference between two 2D rotations/directions?
I want to test if one rotation is within 10° of another. I would just subtract, but there are some problems because I want to keep each rotation between 0 and 359. E.g. 0 is within 10° of 359, but simple subtraction would claim that they're 359 degrees apart.
t1 and t2.d = mod (abs (t1 - t2), 360) if (d > 180) d = 360 - d if (d <= 10) "Hooray!!!" One easy way is to check if the difference is greater than 180 or less than -180. If it is, you can add or subtract 360 to one of the values and then get your difference.
Example:
if(r1-r2 > 180) //r1 > r2 r1 = r1-360; else if(r1-r2 < -180) //r1 < r2 r1 = r1+360; //then check the difference diff = r1-r2; Note that above fails for r1=720 and r2<=0. I would like this...
d = mod (r1 - r2), 360) if(d >= 180) //r1 > r2 d = d-360; else if(d < -180) //r1 < r2 d = d+360; 
