<div>Dear</div>
<div> Sir,</div>
<div> Thank you very much, for your nice reply, i now how to convert from Marcator Space to Lat lon space,</div>
<div> Thank once more</div>
<div> </div>
<div>Suraj<br><br> </div>
<div><span class="gmail_quote">On 11/15/07, <b class="gmail_sendername">Eric Altshuler</b> <<a href="mailto:ela@cola.iges.org">ela@cola.iges.org</a>> wrote:</span>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Dear Suru Polade,<br><br>In the Mercator projection the grid interval in latitude is not constant. It varies from north to south. If you use a constant grid interval in your YDEF statement, your plot will be incorrect. You need to specify each individual latitude like this:
<br><br>YDEF 121 levels LAT_1 LAT_2 LAT_3 ... LAT_121<br><br>To find out the values of the latitudes, you need to transform the location of each grid point in Mercator-projection space to lat-lon space. There are formulas that can be used to do this, but I'm not familiar with the case where the standard latitude is not on the equator (
22.875N in your case). If the original source of your data is in netcdf or grib format, the metadata may include the latitude values.<br><br>Your model may have resolution of "X" km but this does not mean the grid interval is the same everywhere in your domain. Also, the post-processed output data may have a different resolution and/or be on a different grid than your model's native grid.
<br><br>Best regards,<br><br><br>Eric L. Altshuler<br>Assistant Research Scientist<br>Center for Ocean-Land-Atmosphere Studies<br>4041 Powder Mill Road, Suite 302<br>Calverton, MD 20705-3106<br>USA<br><br>E-mail: <a href="mailto:ela@cola.iges.org">
ela@cola.iges.org</a><br>Phone: (301) 902-1257<br>Fax: (301) 595-9793<br><br>----- Original Message -----<br>From: "Suru Polade" <<a href="mailto:gr.suru@GMAIL.COM">gr.suru@GMAIL.COM</a>><br>To: <a href="mailto:GRADSUSR@LIST.CINECA.IT">
GRADSUSR@LIST.CINECA.IT</a><br>Sent: Wednesday, November 14, 2007 12:48:38 AM (GMT-0500) America/New_York<br>Subject: Re: Mercator projection in Grads<br><br><br><br><br>Dear<br><br>       Sir<br><br>              I have emission field from WRF-Chem model over the Indian Region, at the resolution of 1/4 Deg,
<br><br>        with<br><br>                True Latitude 1 =  22.875<br><br>                Center   Lat   =   22.875<br><br>               Center     LON =  Â
82.875<br><br>                DX                 =    1/4 DegÂ<br><br>Â<br><br>         North West  corner Lat Lon ( 36.79, 66.77)           Â<br><br>          South West corner Lat Lon (
7.33, 66.77)<br><br>         North East  Corner Lat Lon (36.79, 98.98)<br><br>         South East Corner Lat Lon ( 7.38, 98.98)<br><br>Â<br><br>if with 1/4 deg we are calculation number of Grid it will comeÂ
<br><br>      North South Grid number 117Â<br><br>      West East Grid number   129<br><br>Â<br><br>but in WRF-SI, Dx we need to give in Km<br><br>if considering 1 Deg = 110 Km then dx will come 27.5 km
<br><br>that will create 121 X 121 Grid with same center and corner lat lon for Mercator projection Â<br><br>Â<br><br>so if giving 121 X 121 in ctl file then emission field is shifting from it's original lat lon position.
<br><br>Â<br><br>i am attaching here data file gs file and ctl file, can you please go through it<br><br>Â<br><br>Â Â Â Â Â Â<br><br>Â your sincerely<br><br>Â<br><br>Suraj<br>Â<br>On 11/13/07 , Brian Doty < <a href="mailto:doty@cola.iges.org">
doty@cola.iges.org</a> > wrote:<br><br>A Mercator grid is typically rectangular in lat/lon, and can be dealt<br>with using the "levels" keyword on the ydef statement in the<br>descriptor file... Brian<br><br>
On Nov 13, 2007 , at 5:43 AM, Suru Polade wrote:<br><br>> I have a pre-projected field in a Mercator projection<br>><br>>Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Is there any way in grads to work with Mercator<br>
> projection, as this projection is not there for pre-projected data.<br>><br></blockquote></div><br>