Windvectormap

[dipak sahu]

Dear Amjad
     Is it atan2(u,v).........or atan2(v,u)..............
     I hope it's atan2(v,u)........

regards
dipak

On Thu, Nov 12, 2009 at 5:46 PM, Muhammad Amjad <amjadozi at gmail.com> wrote:

> Dear Chris,
>
> Could you please check with the following formula:
> wdir=atan2(u,v)/0.01745329 +180
> The size of wind represents the wind speed. So, I don't think the dispariy
> among the vectors can be removed.
>
> Cheers,
> Amjad.
>
>
>
> On 11/9/09, Chris Hayes <c.hayes at weeronline.nl> wrote:
>>
>> dear group,
>>
>> I need to plot the wind directions for stations with equally sized arrows.
>>
>> My dataset contains the direction in degrees (0-360).
>>
>> I use the gxout=vector map which requires a u and a v vector component
>> (i.e. the vertical and horizontal vector component).
>>
>> u
>> |      /winddir
>> |    /
>> |  /
>> |/___ v
>>
>>
>> I calculate u as -sin(winddir * pi/180)
>> I calculate v as -cos(winddir * pi/180)
>>
>> resulting in the display-command    ' -8*(sin(winddir * 0.0175)) ;
>> -8*(cos(winddir * 0.0175)) '
>> (where 8 makes the size of the arrow, which usually represents windspeed
>> but here is desired to be constant)
>>
>>
>> The direction of the arrows looks fine.
>> But some maps have only tiny arrows and some maps have only longtailed
>> arrows.
>> I cannot see a pattern. I have no mixed maps with tiny and large arrows.
>>
>> Should I change my formula, or the way I give the display command?
>>
>> thanks,
>> Chris
>>
>>
>>
>
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