(PHP 4, PHP 5)
atan2 — Arc tangent of two variables
This function calculates the arc tangent of the two variables 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 function returns the result in radians, which is between -PI and PI (inclusive).
The arc tangent of y /x in radians.