How to map atan2 to degrees 0-360

Question

atan2 y  x  has that discontinuity at 180   where it switches to -180    0   going clockwise  How do I map the range of values to 0    360    here is my code  CGSize deltaPoint   CGSizeMake endPoint x - startPoint x  endPoint y - startPoint y   float swipeBearing   atan2f deltaPoint height  deltaPoint width    I m calculating the direction of a swiping touch event given the startPoint and endPoint  both XY point structs  The code is for the iPhone but any language that supports atan2f   will do

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The R packages geosphere will calculate bearingRhumb  which is a constant bearing line given an origin point and easting northing  The easting and northing must be in a matrix or vector  The origin point for a wind rose is 0 0  The following code seems to readily resolve the issue   windE lt -wind uasE windN lt -wind vasN wind matrix lt -cbind windE  windN  wind wind dir lt -bearingRhumb c 0 0   wind matrix  wind wind dir lt -round wind wind dir  0

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A formula to have the range of values from 0 to 360 degrees   f x y  180-90  1 sign x     1-sign y 2  -45  2 sign x   sign y        - 180 pi    sign x y  atan  abs x -abs y    abs x  abs y

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I have 2 solutions that seem to work for all combinations of positive and negative x and y   1  Abuse atan2    According to the docs atan2 takes parameters y and x in that order  However if you reverse them you can do the following   double radians   std  atan2 x  y   double degrees   radians   180   M PI  if  radians  lt  0        degrees    360       2  Use atan2   correctly and convert afterwards  double degrees   std  atan2 y  x    180   M PI  if  degrees  gt  90        degrees   450 - degrees    else       degrees   90 - degrees

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angle   Math atan2 x y  180 Math PI    I have made a Formula for orienting angle into 0 to 360  angle   Math ceil  -angle   360     360

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Just add 360   if the answer from atan2 is less than 0

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x  gt  0   x    2 PI   x     360    2 PI

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Jason S  your  fmod  variant will not work on a standards-compliant implementation   The C standard is explicit and clear  7 12 10 1   the fmod functions        if y is nonzero  the result has the same sign as x   thus   fmod atan2 y x  M PI 180 360    is actually just a verbose rewriting of   atan2 y x  M PI 180   Your third suggestion  however  is spot on

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Or if you don t like branching  just negate the two parameters and add 180   to the answer    Adding 180   to the return value puts it nicely in the 0-360 range  but flips the angle  Negating both input parameters flips it back

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erikkallen is close but not quite right   theta rad   atan2 y x   theta deg    theta rad M PI 180     theta rad  gt  0   0   360     This should work in C     depending on how fmod is implemented  it may be faster or slower than the conditional expression   theta deg   fmod atan2 y x  M PI 180 360     Alternatively you could do this   theta deg   atan2 -y -x  M PI 180   180    since  x y  and  -x -y  differ in angles by 180 degrees

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Solution using Modulo  A simple solution that catches all cases   degrees    degrees   360    360       360 for implementations where mod returns negative numbers   Explanation  Positive  1 to 180  If you mod any positive number between 1 and 180 by 360  you will get the exact same number you put in  Mod here just ensures these positive numbers are returned as the same value   Negative  -180 to -1  Using mod here will return values in the range of 180 and 359 degrees   Special cases  0 and 360  Using mod means that 0 is returned  making this a safe 0-359 degrees solution

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double degree   fmodf  atan2 x  y     180 0   M PI     360  360     This will return degree from 0  -360   counter-clockwise  0   is at 3 o clock

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This is what I normally do   float rads   atan2 y  x   if  y  lt  0  rads   M PI 2 f   rads  float degrees   rads 180 f M PI

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An alternative solution is to use the mod    function defined as       function mod a  b   return a - Math floor  a   b    b    Then  with the following function  the angle between ini x y  and end x y  points is obtained  The angle is expressed in degrees normalized to  0  360  deg  and North referencing 360 deg       function angleInDegrees ini  end            var radian   Math atan2  end y - ini y    end x - ini x     radian  -PI PI          return mod radian   180   Math PI   90  360

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theta rad   Math Atan2 y x   if theta rad  lt  0    theta rad   theta rad   2   Math PI       if neg   add 2 PI to it theta deg    theta rad M PI 180             convert from radian to degree    or theta rad   Math Atan2 y x   theta rad    theta rad  lt  0    theta rad   2   Math PI   theta rad  theta deg    theta rad M PI 180      -1 deg becomes  -1   360    359 deg -179 deg becomes  -179   360    181 deg

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Here s some javascript   Just input x and y values   var angle    Math atan2 x y     180 Math PI    360    360

[math] How to map atan2() to degrees 0-360

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