Windvectormap

[Muhammad Amjad]

Dear dipak,

I think you are right............

Amjad.






On Sun, Nov 15, 2009 at 9:40 PM, dipak sahu <dipakmath at gmail.com> wrote:

> 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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