Internal Grads Grid

[Mike Fiorino]

Ben,

your .ctl is not preprojected, but you could make it preprojected and then
the change res via xdef/ydef would work.  a better way would be regrid2,
see: http://wxmap.net/mike/grads/udf/

Cheers,
Mike

> -----Original Message-----
> From: GRADSUSR at LIST.CINECA.IT
> [mailto:GRADSUSR at LIST.CINECA.IT] On Behalf Of Ben Quinn
> Sent: Friday, April 14, 2006 7:33 PM
> To: GRADSUSR at LIST.CINECA.IT
> Subject: Internal Grads Grid
>
> Hi all,
>
> I'm downloading 1 degree (subregion) GFS forecast gribs from
> the NCEP FTP2U servers and creating the control files with
> gribtoctl.pl.  Creating Grads plots with the 1 degree grid is
> fine but i'm also running a script that extracts vertical
> profiles from the gribs via Grads for use in vertical
> sounding plots and i wanted Grads to interpolate to a finer
> resolution - ie at the moment Grads rounds off any lat/lon
> figures i give it to the nearest whole degree, but ideally
> i'd like to extract data in .2 degree increments at least.
> Reading the manual, it sounded easy enough to do :
>
> " It is very important to point out that the internal GrADS
> grid can be any grid as it is completely independent of the
> preprojected data grid. Thus, there is nothing stopping you
> displaying preprojected data on a very high res lon/lat grid
> (again, defined in the .ctl by xdef and ydef). In fact, you
> could create and open multiple .ctl files with different
> resolutions and/or regions which pointed to the same
> preprojected data file."
>
> But for some reason when i alter xdef and ydef in the control
> file Gribmap returns an error when trying to open the grib
> file.  I've tried a few different combinations - running
> gribmap with the original control file, then altering it and
> trying to open it all in Grads etc but to no avail.
> I'm missing something somewhere.  A cut and paste from the
> original control files gribtoctl is producing :
>
> set ^gfs.t18z.pgrbf%f3
> index ^gfs.t18z.pgrbf000.idx
> undef 9.999E+20
> title gfs.t18z.pgrbf000
> *  produced by grib2ctl v0.9.12.5p34c
> dtype grib 255
> options template
> options yrev
> ydef 36 linear -45.000000 1
> xdef 51 linear 110.000000 1.000000
> tdef 61 linear 18Z14apr2006 3hr
> zdef 21 levels
> 1000 975 950 925 900 850 800 750 700 650 600 550 500 450 400
> 350 300 250 200 150 100 vars 16
>
> Altering ydef and xdef (for say a .5 degree grid) to
>
> ydef 73 linear -45.000000 0.5
> xdef 102 linear 110.000000 0.500000
>
> Doesn't work for some reason... any help would be much appreciated!
>
>
> Ben Quinn
>
> The Brisbane Storm Chasers Homepage
> http://www.bsch.au.com
> The Australian Severe Weather Association
> http://www.severeweather.asn.au
>