Re: draw simple vector field

As indicated in the documentation, you need the wind components (u, v)
to draw the arrows. NCL calculates the direction internally.

It would be surprising if u,v are not on the source file. However, if
you have the speed (wspd) and direction (wdir) only, you can
extract the wind components manually:

       rad = 0.01745329
       u = -wspd*sin(wdir*rad)
       v = -wspd*cos(wdir*rad)

Also, if you have 6.1.0 or higher there is a functon:
http://www.ncl.ucar.edu/Document/Functions/Contributed/wind_component.shtml

Good luck
On 3/14/13 2:30 AM, Yann Bertrand wrote:
>
>
>
> Hi,
> i try to draw a vector field :
> but i don't know how to get u and v (2-dimension)
> and the direction (which is the main information i want to get.
> Here's a piece of code.
> Thanks in advance.
>
> ncl_filedump gives :
>
> float DIR ( lv_OSEQD0, lat_0, lon_0 )
> center :US National Weather Service - NCEP (WMC)
> production_status :Operational products
> units :Degree True
>
> _FillValue :1e+20
> grid_type :Latitude/longitude
> parameter_template_discipline_category_number :( 0, 10, 0, 7 )
>
> level_type :Ordered Sequence of Data
> forecast_time :96
> forecast_time_units :hours
>
>
> what i've tried :
>
> outfile="out"
> grib_file="grib.grib2"
> fin = addfile(grib_file,"r")
>
> ; get variable:
>
> dir3d = fin->DIR
>
> dir = dir3d(0,:,:)
>
> wks = gsn_open_wks("ps",outfile) ; open wk station
>
>
> res = True
>
>
> res@vcGlyphStyle = "LineArrow"
>
>
> res@mpLimitMode="latlon"
> res@mpMinLonF = -33
>
> res@mpMaxLonF = 2
> res@mpMinLatF = 21
> res@mpMaxLatF = 37
>
> res@mpProjection = "LambertConformal"
>
>
> plot = gsn_csm_vector_scalar(wks, dir(:,:), dir(:,:), dir3d(:,0,0), res)
>
>
>
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Received on Mon Mar 18 11:22:25 2013