Menu
Normally, polar coordinates go from 0 to π to 2π (just before 2π really, as it equals 0 again). However, when using the JavaScript atan2() function, I'm getting a different, weird range:
Cartesian X | Cartesian Y | Theta (θ)
===========================================================
1 | 0 | 0 (0 × π)
1 | 1 | 0.7853981633974483 (0.25 × π)
0 | 1 | 1.5707963267948966 (0.5 × π)
-1 | 1 | 2.356194490192345 (0.75 × π)
-1 | 0 | 3.141592653589793 (1 × π)
-1 | -1 | -2.356194490192345 (-0.75 × π)
0 | -1 | -1.5707963267948966 (-0.5 × π)
1 | -1 | -0.7853981633974483 (-0.25 × π)
As you can see, after it reaches π (180°), it jumps down to –π (–180°), and proceeds back up to 0. How can I get it to use the range {0, ..., 2π} instead of {–π, ..., π}? I've been trying to think of every calculation to "fix" the values, but I would also like to know why JavaScript chooses this range instead of the typical polar range. Thanks!
998
atan2() function returns the angle in the plane (in radians) between the positive x-axis and the ray from (0, 0) to the point (x, y), for Math.
atan2(0,0) may lead to 0.0, 1.0, INF, NAN , etc. It is not specified other than something is returned.
Arc tangent of two numbers, or four-quadrant inverse tangent. ATAN2(y,x) returns the arc tangent of the two numbers x and y. It is similar to calculating the arc tangent of y / x, except that the signs of both arguments are used to determine the quadrant of the result. The result is an angle expressed in radians.
In conclusion, if you are calculating something that ranges between -90 and 90 degrees like latitude, use arctan. If calculating an angle that can be between -180 and 180 degrees, use arctan2.
It's pretty standard for atan2 to return angles in that range; for instance, that's what the atan2 in the C standard library does.
If you want 0..2pi instead of -pi..pi, test whether the result is negative and add 2pi if it is.
120
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
