[gradsusr] lats4d issues

Tue Aug 10 14:09:14 EDT 2010

I had a similar artifact in grib output from lats4d.

My scripts -

1st script downloads NAM from Nomads HA and writes flat files with .ctl
file

2nd script makes a grib of the flat file.

The resulting grib, when re-viewed in grads or commercial programs, had
missing points on the diagonal from lower left row #2 toward the upper
right.  Hence, each row was progressively shifted toward the right.

The problem was in the lat & lon increments in the .ctl file.     I was
using 6 decimal places.

            Changing the lat & lon increments to 4 decimal places
eliminated the problem, so far.

grads-1.9.0-rc1.win32-r3.win32_superpack 

Windows Vista

Thank you,

Herb Philbrick

     voice 219-787-3321

     fax    219-787-2690

     Herb.Philbrick at arcelormittal.com
<mailto:Herb.Philbrick at arcelormittal.com> 

________________________________

From: gradsusr-bounces at gradsusr.org
[mailto:gradsusr-bounces at gradsusr.org] On Behalf Of Arlindo da Silva
Sent: Wednesday, August 04, 2010 9:45 PM
To: GrADS Users Forum
Subject: Re: [gradsusr] lats4d issues

On Mon, Aug 2, 2010 at 1:59 PM, Matt Brewer <mcbrewer83 at yahoo.com>
wrote:

	Folks,
	I am using lats4d to convert NCEP's NARR data (grib) to netCDF.
It only kind of worked. This is what I type into the command line: 

	lats4d -i narr-a_221_19790101_0000_000.sub -o narr2009.nc -ftype
ctl -lon -160 -90 -lat 25 65  -time 0z1jan2009 21z31dec2009 -mxtimes
2920 -levs 925mb -xvars ugrdprs vgrdprs ugrd10m vgrd10m msletmsl
prmslmsl

	This works fine except for one issue. It seems to be totally
messing up the axis dimensions, causing data to be in incorrect lat/lon
locations.Notice how I asked for data from 160W to 90W and 25N to 65N,
so with the longitude, that is a span of 70 degrees, and for latitude,
it is 40 degrees. So I should get back a geopot. height matrix of
121x211 (there are data points every 1/3rd degree). It seems, in matlab
at least, that I get an array of 122x212. And so what happens is the
first point on the second array actually gets saved in the 212th place
in the first array, so the second line starts out with what is supose to
be the second point in the array. Make sense? When I put the nc file
into grads, it has similar issues as well....so something wierd is going
on when I run the lats4d script....I just don't know what. So if anyone
has any ideas of what is goin on, please help!!!

The first step is to make sure GrADS is reading your GRIB file
correctly. Go ahead, start GrADS, open your GRIB file, plot it and see
if it is doing it correctly:

ga-> open narr-a_221_19790101_0000_000.sub

ga-> d something

If this is pre-projected data, make sure your PDEF is correct. Once you
sort this out, the netcdf version should produce the same results. (Our
regression tests do just that: reads a GRIB file, converts to netcdf,
then reads the netcdf file back and checks if it gets exactly the same
values.)

One important detail: when asking for help, you need to let us know the
particular version of grads, lats4d, and your operating system;
basically, the otput of "q config".

   Arlindo

	Matt

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-- 
Arlindo da Silva
dasilva at alum.mit.edu

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