# [gradsusr] Plot vector - geographic X trigonometric system

Gabriel - ud Carvalho gabriel.ud at gmail.com
Mon Sep 27 15:26:11 EDT 2010

```I think that I was not clear,
I can´t do this suggestion because the 'sin' function is oriented to the
trigonometric system, which isn´t the system in which my data is oriented.
For instance, in my data, a 270 degrees is equivalent to 180 degrees in the
trigonometric system.

I hope I am more clear now, even thoug the roughness of my english...:)

Gabriel  Carvalho

2010/9/27 Jeffrey Duda <jdduda at iastate.edu>

> Gabriel,
> As long as your data contains wind direction oriented such that 0 deg in
> your data refers to a wind blowing to the north (or from the south), then
> your components can be broken down as:
>
> u = wind_magnitude * sin(direction)
> v = wind_magnitude * cos(direction)
>
> Of course, when actually putting these computations into Grads you will
> want to change "direction" from degrees to radians.
>
> Jeff Duda
>
> On Mon, Sep 27, 2010 at 12:34 PM, Gabriel - ud Carvalho <
> gabriel.ud at gmail.com> wrote:
>
>> Hello you all!
>> Here is the deal:
>> In my data, the wind direction is in degrees, with a geographic
>> representation (wich means that 0 is at the north and goes clockwise),
>> the problem is that to display this data with 'gxout vector', I have to
>> decompose it in 'u' and 'v'. In order to do this, I have to use the
>> trigonometric functions 'sin' and 'cosin'. The problem is here, these
>> functions assume that the input data is with a trigonometric representation
>> (wich means that 0 degrees is eastside and goes anti-clockwise),butthey
>> aren´t, so, it got all messed up.
>>
>> I don´t know what to do,but I believe that this is a common problem,
>> I hope someone will know the answer...
>>
>> Sorry about my poor english,
>>
>> My best regards,
>> Gabriel Carvalho
>>
>>
>>
>>
>> _______________________________________________
>>
>>
>
>
> --
> Jeff Duda
> Iowa State University
> 3134 Agronomy Hall
> www.meteor.iastate.edu/~jdduda
>
> _______________________________________________