[gradsusr] lon lat to km

[Jeff Duda]

These commands will help.

'define dx = 6.371e3*cos(lat*(3.14159/180))*cdiff(lon,x)*(3.14159/180)'
'define dy = 6.371e3*cdiff(lat,y)*(3.14159/180))'

They define grid increments in terms of spatial distance rather than
geographic distance.  If you're trying to change the axes and tick marks,
you'll have to define an origin and define your x and y distances based on
that.  For instance, if you set your lower left domain corner (latitude 0
and longitude 100), then you can define your coordinate distances using

'define xdist = [(lon-100)/dlon]*[dx/2]'
'define ydist = [(lat-0)/dlat]*[dy/2]'

I think this should work, but I haven't tested it myself, so I don't know.
 dlon and dlat are the step values from the XDEF and YDEF lines of the
control file, respectively.

Jeff Duda

On Thu, Jan 31, 2013 at 7:02 AM, wendi harjupa <wendiharjupa at gmail.com>wrote:

> Dear Sir/Madam
>
> I need help
> I have problem with grads command,
> I am not well understand with command gr2XY,
>
> Actually I want to convert the lon 100  to 101, and lat 0 to 1 to distance
> (km)
> let think that lon 100 is 0 km, and lat 0 is 0 km,
>
> what command I can use to convert lon and lat to km?
>
> Thank you very much for your help
>
> best regards,
> --
> -------------
> Wendi Harjupa. ST
> Shimane University Graduate School of Engineering Sciences
> Department of Electronic Control Systems
> Remote Sensing Laboratory
> s119447
> Cellphone : +81-080-4268-6676
> email : wendi at rslab.riko.shimane-u.ac.jp
>
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>


-- 
Jeff Duda
Graduate research assistant
University of Oklahoma School of Meteorology
Center for Analysis and Prediction of Storms
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