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I searched but couldn't find on Google:

My question is, how do I find the opposite direction of an angle, for example 170 degree, how do I calculate the opposite direction in degrees?

Thanks in advance.

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3 Answers

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If you are given an angle $\alpha$, the oppossite angle would be $\alpha+180$. If you need to remain in $[0,360]$ then, you should take $(\alpha+180)\ mod\ 360$ (what in this case it is simply taking $\alpha-180$ if $\alpha+180\ge360$)

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In aviation the 200/20 rule can be used. If your current heading in degree is below 180° e.g. 80° then you add 200 and subtract 20. 80+200=280. 280-20=260. If your current heading in degrees is above 180° then subtract 200 and add 20. E.g. 240-200=40. 40+20=60

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Considering an angle normallized between -180° and 180°, the opposite angle is given by :

if angle == 0 : opposite = 180 // or -180 as you wish
else : if angle > 0 : opposite = angle - 180 else : opposite = angle + 180

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