[gradsusr] Plot vector - geographic X trigonometric system

Jeffrey Duda jdduda at iastate.edu
Mon Sep 27 14:21:20 EDT 2010

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
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> gradsusr at gradsusr.org
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Jeff Duda
Iowa State University
Meteorology Graduate Student
3134 Agronomy Hall
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