Returns the radian value of the arc tangent of specified X and Y coordinates. The arc tangent is the angle from the X-axis to a line passing through the origin and a point with coordinates X,Y. The returned angle is in radians, from -pi to pi, excluding -pi.
float atan2(float Y, float X )
X is the X coordinate of the point.
Y is the Y coordinate of the point.
atan2(1,1)
Returns 0.785 radians.