[wateraction]

Hi,folks! I gotta a kind of stupid easy question that has been confusing me for a while, could anyone help me out?

Question: What's the physical meaning of "velocity angle" when you want to plot a contours about it on a certain surface?(Please see attched sketch map)

In my own opinion, it is the angle between velocity magnitude and the surface that you have chosen to plot a contours, am I right?

Plus: the value of the velocity angle is displayed in the unit of radian instead of degree?

Thank you so much for your time and consideration!