Two Dimensional Vector Angle Calculation
Using this Online Calculator, we can
Calculate the Angle for two vectors v & w
In 2D (Two Dimensional) vector there is only one degree of freedom for 2D rotations. If v and w are normalized
so that |v|=|w|=1, then angle = inverse of cosine (v X w)
where: |v|,|w| is magnitude of v,w.