[gradsusr] Shift in the lattitude while plotting in grads mercator/latlon projction

[Yaqiang Wang]

Mercator projection is longitude equal-interval but not latitude
equal-interval. The ctl without PDEF (Mercator is not supported in PDEF at
present) may approximatively plot the data at low latitude area, but it's
imposible plot the data at exactly position.

On Friday, July 12, 2013, itesh dash wrote:

> The information actually were extracted from in the namelist.wps file
> using WRF2GrAGS which generate the control(ctl) file. For the model I only
> provided the grid resolution(9km), no of grid points in both north south
> (640) and east west(460)  and center latitude and longitude (18.0 and
> 91.0).
>
> The XDEF,YDEF and other params were automatically calculated by WRF2Grads.
> But your guessing may be correct as i have changed the start lat from
> -3.1006 to -2.1006 and the shift is minimized. BUt is this correct way?
>
> I am currently using the mercator projection. I will change to
> lat-lon projection and see if that makes the difference.
>
> Thanks.
>
>
>
>
> On Fri, Jul 12, 2013 at 12:40 AM, James T. Potemra <jimp at hawaii.edu>wrote:
>
>  Itesh:
>
> Your model output is 640 x 460, but your descriptor file has
> xdef = 639 and ydef = 459.  These should be 640 and 460,
> respectively.  Also, I think what Mohsen meant was to make
> sure your starting lat/lon is the same in the descriptor file
> and model grid, i.e., you have 61.1815 as the starting lon
> and -3.1006 as the starting lat.  Are these the same as the
> model grid?
>
> Jim
>
>
> On 7/11/13 7:31 AM, itesh dash wrote:
>
> Dear Mohsen,
>
>  thanks for the response. But I am not even trying to use any script.
> Just by opening and plotting the ctl file.
>
>  Here is my ctl file
>
>  dset ^Jul1013_12.dat
> undef 1.e35
> xdef  639 linear   61.1815   0.0935
> ydef  459 linear   -3.1006   0.0873
> zdef    3 levels
>   850.00000
>   500.00000
>   200.00000
> tdef         8 linear 12z10jul2013  6hr
> vars 1
> HGT 0 0 Terrain Height
> endvars
>
>  The wrf model ran with mercator projection 640 x 460 grid points 9 km
> resolution.
>
>  I could not figure out why the shift is there. Is there a way i can
> balance the shift.
>
>  regards,
> itesh
>
>
> On Thu, Jul 11, 2013 at 11:58 PM, Mohsen Soltani <soltani.clima at gmail.com>wrote:
>
>  itesh,
>
>  Make sure Lat/Lon in your .ctl file are the same as your script!
>
>  Mohsen
>
>  --
> April showers bring May flowers!
>  --
> *Mohsen Soltani, M.Sc.*
> Climatology Grad Student,
> Department of Climatology, Faculty of Geography,
> University of Tehran, Tehran, Iran
> voice: (+98) 9119772934
> e-mail: soltani.clima at gmail.com
>
>
>  On Thu, Jul 11, 2013 at 9:05 AM, itesh dash <itesh at rimes.int> wrote
>
>

-- 
*************************************************
Dr. Yaqiang Wang
Chinese Academy of Meteorological Sciences (CAMS)
46, Zhong-Guan-Cun South Avenue
Beijing, 100081
China

yaqiang.wang at gmail.com

http://www.meteothinker.com
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