Reference: arctan2
arctan2(x, y) returns the angle between the positive x-axis and the vector from the origin to the point (x, y) ∈ R^2, within the interval ]-π, π].
arctan2(x, y) returns the angle between the positive x-axis and the vector from the origin to the point (x, y) ∈ R^2, within the interval ]-π, π].