Help to read grib files: FINAL SOLUTION
oluseun idowu
oluseun_idowu at YAHOO.COM
Thu Apr 13 04:03:48 EDT 2006
Thank you all for your help. I have written to the UK office to see if the grib files can be properly encoded.
Can you pls tell me the commands (step by step) to use when I want to, create the ctl with grib2ctl.pl and modify the X and Y steps? And again, to change the name of the variable so that I can input the final ctl file and eventually able to plot with GrADS.
Thanks
Henrique Barbosa <hmjbarbosa at GMAIL.COM> wrote: Dear Oluseun,
There is a program call wgrib which is very usefull to find out what is
inside a misterius grib file. Here's the output I have from runing it
with your sample file:
71 hbarbosa at azusa hbarbosa> wgrib -verf -V sample_grib_file.grib
Undefined parameter table (center 74-2 table 160), using NCEP-opn
rec 1:0:date 2006032218 PVORT kpds5=4 kpds6=205 kpds7=1 levels=(0,1)
grid=255 48hr fcst:
PVORT=Pot. vorticity [km^2/kg/s]
timerange 0 P1 48 P2 0 TimeU 1 nx 432 ny 432 GDS grid 0 num_in_ave
0 missing 0
center 74 subcenter 2 process 1 Table 160
latlon: lat -37.500000 to 40.080000 by -32.767000 nxny 186624
long 340.000000 to 57.580000 by -32.767000, (432 x 432) scan
64 mode 0 bdsgrid 1
min/max data 269.25 314.125 num bits 24 BDS_Ref 269.25 DecScale 0
BinScale -18
rec 2:560228:date 2006032300 PVORT kpds5=4 kpds6=205 kpds7=1
levels=(0,1) grid=255 54hr fcst:
PVORT=Pot. vorticity [km^2/kg/s]
timerange 0 P1 54 P2 0 TimeU 1 nx 432 ny 432 GDS grid 0 num_in_ave
0 missing 0
center 74 subcenter 2 process 1 Table 160
latlon: lat -37.500000 to 40.080000 by -32.767000 nxny 186624
long 340.000000 to 57.580000 by -32.767000, (432 x 432) scan
64 mode 0 bdsgrid 1
min/max data 266.75 310.375 num bits 24 BDS_Ref 266.75 DecScale 0
BinScale -18
As you can see, you grib file is wrongly encoded and it reports that
the step in X and Y
directions are -32.767 degrees.... and that is exactly what you get when you run
grib2ctl.pl
Well, what I did then was to create the ctl with grib2ctl.pl and
modify the X and Y steps.
I did it like:
X-step = (40.08 - (-37.5)) / 432 = 0.17958333
Y-step = (57.58 - (340-360)) / 432 = 0.17958333
Oh, I also changed the name of the variable because your grib file
uses a non-standard
table and grib2ctl was confused... So here is the final ctl for you file:
dset ^sample_grib_file.grib
index ^sample_grib_file.grib.idx
undef 9.999E+20
title sample_grib_file.grib
* produced by grib2ctl v0.9.12.5p33k
dtype grib 255
ydef 432 linear -37.500000 0.17958333
xdef 432 linear 340.000000 0.17958333
tdef 2 linear 18Z22mar2006 6hr
zdef 1 linear 1 1
vars 1
temp 0 4,205,1 ** temp
ENDVARS
now you just have to run gribmap on it and you should get it right.
I did and I am sending attached an image of the temperature field.
By the way, I would write to the UKMet guys if I were you. Just to check
why their grib files are encoded with the wrong X-Y-step.
Cheers,
Henrique
On 4/12/06, Henrique Barbosa wrote:
> Dear Oluseun,
>
> Verify the invalid descriptor. If you have 432 X-values, your X-step
> cannot be -32.767... that would mean almost going 40 times around
> the globe!
>
> Please check the grads help pages:
>
> http://grads.iges.org/grads/gadoc/descriptorfile.html
>
> There you will learn howto properly setup XDEF
>
> Cheers,
> Henrique
>
>
> On 4/12/06, oluseun idowu wrote:
> >
> > Dear Diane,
> > Many thanks for your help. I gave the command
> >
> > [oluseun at b129pc124 ~]$ gribmap -v -i sample_grib_file.ctl
> >
> > This is the error message
> >
> > Open Error: Missing or invalid dimension increment value
> > --> The invalid description file record is:
> > --> xdef 432 linear 340.000000 -32.767000
> >
> >
> > The data file was not opened.
> > File name is: sample_grib_file.ctl
> >
> > Anyway as you suggested, I attach the file to this email and again, the data
> > was received from UK Met Office
> > from their limited area model
> >
> > I will expect your reply. Thanks once more!
> >
> > Idowu
> >
> > Below is the description of the file as given to me from UK Met Office.
> > ----------------------------------------------------------------------
> > OK, I've attached a sample grib file to this e-mail. It contains the
> > level-1 model temperature field at T+48 and T+54. Once you confirm you
> > can read this I'll put the full data-set for one forecast onto our ftp
> > server: email.metoffice.gov.uk. This will be ~660Mb of data. We can get
> > these file-sizes down if you can work with data over a smaller
> > geographical area or you don't need all the vertical levels.
> >
> > Luke.
> > ----------------------------------------------------------------------------------------------------------------------------------------------------
> >
> >
> >
> > Diane Stokes wrote:
> >
> > Dear Idowu,
> >
> > That's just a warning message. It's possible that reasonable variable
> > names were chosen for your data. Did you try to run gribmap on the new
> > ctl file yet?
> >
> > gribmap -v -i sample_grib_file.grib.ctl
> > The "-v" (verbose) option is important as it will tell you which records
> > matched. Other options may be necessary as well, but the above is a start.
> >
> > If g ribmap does not work, please post your control file to the list.
> >
> > That may help us to help you.
> >
> > Also, where did you get your sample grib file, sample_grib_file.grib?
> >
> > Diane
> >
> >
> > oluseun idowu wrote:
> > > Dear Diane,
> > > Thanks for your help. I can find the grib2ctl.pl in my system now though
> > > under grib_files folder. The next problem is that in an attempt to make
> > > grib.ctl file the error message below was reported. Any further help?
> > >
> > > [oluseun at b129pc124 ~]$ ./grib_files/grib2ctl.pl sample_grib_file.grib
> > > >sample_grib_file.grib.ctl
> > >
> > > Undefined parameter table (center 74-2 table 160), using NCEP-opn
> > >
> > > Undefined parameter table (center 74-2 table 160), using NCEP-opn
> > >
> > >
> > >
> > >
> > > */Diane Stokes /* wrote:
> > >
> > > The web address is actually:
> > >
> > >
> > http://www.cpc.ncep.noaa.gov/products/wesley/grib2ctl.html
> > >
> > > There's some useful information there in addition to the link to the
> > > script.
> > >
> > > Diane
> > >
> > > See Hai Ooi wrote:
> > > > Dear Oluseun Idowu,
> > > >
> > > > The grib2 ctl.pl is available in the website you
> > > > indicated
> > > > [http://www.cpc.noaa.gov/products/wesley/grib2ctl.html]
> > > > Anyway, hope the attached perl file can help you to
> > > > resolve your problem. If in doubt, please refer to the
> > > > usage document in the above-mentioned webpage.
> > > >
> > > > Best regards.
> > > >
> > > > Ooi
> > > >
> > > >
> > > >
> > > > Send instant messages to your online friends
> > > http://uk.messenger.yahoo.com
> > >
> > >
> > >
> > ------------------------------------------------------------------------
> > > To help you stay safe and secure online, we've developed the all new
> > > *Yahoo! Security Centre*
> > > .
> > >
> >
> > --
> > Diane Stokes
> > Environmental Modeling Center
> > National Weather Service/NOAA
> >
> >
> >
> >
> >
> > ________________________________
> > Yahoo! Cars NEW - sell your car and browse thousands of new and used cars
> > online search now ________________________________
> >
> >
> >
> >
>
---------------------------------
Yahoo! 360° NEW – Your one place to blog, create, publish & share!
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20060413/6f297709/attachment.html
More information about the gradsusr
mailing list