Short memo for angle calculation using atan2

Angle and arc-tangent function (in C/C++)

θ = atan2(x,y)
θ' = -(360 - θ)

#1: Bearing and an arc-tangent function

b = atan2(E, N)

Angle between 'N' axis and a vector.

CW is positive.

#2: Rotation angle about an axis and an arc-tangent function

ω = -atan2(x, y)

Angle between 'Y' axis and a vector.

CCW is positive.