Splitting Wind direction into four quadrants

Hello,

I had u & V component of wind. I converted them to wind speed & direction, using

 wind_speed=sqrt((u^2)+(v^2));
 wind_direction=180 + atand(u/v);

The problem is wind direction is not splitting into quadrants. As done here http://wx.gmu.edu/dev/clim301/lectures/wind/wind-uv.html

Answer 1

[Chad Greene]

I think Kelly is partly correct. You'll need the four-quadrant version of atand, which is called atan2d.

Another quick tip: Instead of this:

wind_speed=sqrt((u^2)+(v^2));

you can use

wind_speed=hypot(u,v);

which is less prone to typos.

[Student new]

Thanks alot Star Strider, you made my day..

You are right i was doing a mistake of (/). But i can not see comment of Star strider now..

Answer 2

[Kelly Kearney]

As mentioned in those lecture notes, you'll need to use atan2 instead of atan (not atand either... your inputs aren't in degrees!) to get the four-quadrant result you want.

[Student new]

I used v=180 + atand(u/v); and the result is fine for positive values of v.

If appear negative value of v then this formula fails

[Kelly Kearney]

Right, never mind on the degrees comment. I was mistakenly reversing inputs and outputs in my head. But as Chad answered, you still need the atan2d variant.

[Student new]

Thanks alot Kelly Kearney