OpenDAP GRIB Retrieval from Nomads

[Mark Hess]

Jim,

Excellent!  That is more than enough to get me started.  Thanks very much for the detailed explanation and sample - very helpful for a GrADS/OpenDAP rookie like myself!

Mark

  ----- Original Message ----- 
  From: James T. Potemra 
  To: GRADSUSR at LIST.CINECA.IT 
  Sent: Thursday, November 12, 2009 11:05 AM
  Subject: Re: OpenDAP GRIB Retrieval from Nomads


  Hi Mark:

  Should be pretty straightforward.  Just follow the link you give below
  and you should see a list of the GDS catalog at nomads (the listing has
  names like gfs20091101).  Select whichever date in which you are
  interested, and you should see a page with the data set catalog.  For
  example, I just clicked on the top one gfs20091014 and got a list with
  gfs_00z, gfs_00z_anl, etc.  Again, pick the one of interest and click on
  the "info" link.  E.g., I clicked on the "info" link next to gfs_00z
  (the direct URL is
  http://nomads.ncep.noaa.gov:9090/dods/gfs/gfs20091014/gfs_00z.info).
  All you need is the "OPeNDAP/DODS Data URL" listed at the top, again in
  this case it is
  http://nomads.ncep.noaa.gov:9090/dods/gfs/gfs20091014/gfs_00z
  (Note here that you can't always assume the syntax of the DODS Data URL
  will be similar to the catalog URL, but in this case it happens to be).
  So, now all you need to do is fire up GrADS (or gradsdods depending on
  your binary version), then type in "sdfopen xxx" where "xxx" is the DODS
  data URL from above.  You should then have total access to the data set,
  at which point you'll first be amazed at the simplicity with which you
  can access data without actually having to transfer/reformat/etc., and
  then you'll be looking for a way to thank all the brilliant minds that
  provide us with this capability.  The final step, if you really want to
  download, is just "set lat ...", "set lon...", "set lev...", "set
  time..", "set gxout fwrite" and "d variable".

  Jim

  PS.  Here's what it looks like for the sample file:

  grads -l

                Welcome to the OpenGrADS Bundle Distribution
                --------------------------------------------

  For additional information enter "grads -h".

  Starting
  "/usr/local/grads-2.0.a7.oga.2/Contents/Linux/Versions/2.0.a7.oga.2/x86_64/grads
  -l " ...


  Grid Analysis and Display System (GrADS) Version 2.0.a7.oga.2
  Copyright (c) 1988-2008 by Brian Doty and the
  Institute for Global Environment and Society (IGES)
  GrADS comes with ABSOLUTELY NO WARRANTY
  See file COPYRIGHT for more information

  Config: v2.0.a7.oga.2 little-endian readline printim grib2 netcdf
  hdf4-sds hdf5 opendap-grids,stn athena geotiff
  Issue 'q config' command for more information.
  Loading User Defined Extensions table
  </usr/local/grads-2.0.a7.oga.2/Contents/Linux/Versions/2.0.a7.oga.2/x86_64/gex/udxt>
  ... ok.
  GX Package Initialization: Size = 11 8.5
  ga-> sdfopen http://nomads.ncep.noaa.gov:9090/dods/gfs/gfs20091014/gfs_00z
  Scanning self-describing file:
  http://nomads.ncep.noaa.gov:9090/dods/gfs/gfs20091014/gfs_00z
  SDF file http://nomads.ncep.noaa.gov:9090/dods/gfs/gfs20091014/gfs_00z
  is open as file 1
  LON set to 0 360
  LAT set to -90 90
  LEV set to 1000 1000
  Time values set: 2009:10:14:0 2009:10:14:0
  E set to 1 1
  ga-> q file
  File 1 : GFS fcst starting from 00Z14oct2009, downloaded Oct 14 04:24 UTC
    Descriptor: http://nomads.ncep.noaa.gov:9090/dods/gfs/gfs20091014/gfs_00z
    Binary: http://nomads.ncep.noaa.gov:9090/dods/gfs/gfs20091014/gfs_00z
    Type = Gridded
    Xsize = 360  Ysize = 181  Zsize = 26  Tsize = 61  Esize = 1
    Number of Variables = 139
       absvprs  26  t,z,y,x  ** (1000 975 950 925 900.. 70 50 30 20 10)
  none absolute vorticity [1/s]
       no4lftxsfc  0  t,y,x  ** surface none best (4 layer) lifted index [k]
       no5wava500mb  0  t,y,x  ** 500 mb none 5-wave geopotential height
  anomaly [gpm]
       no5wavh500mb  0  t,y,x  ** 500 mb none 5-wave geopotential height
  [gpm]
  ....

  ga-> set lat -90 90
  LAT set to -90 90
  ga-> set lon 130 150
  LON set to 130 150
  ga-> set t 1
  Time values set: 2009:10:14:0 2009:10:14:0
  ga-> set z 1
  LEV set to 1000 1000
  ga-> set gxout fwrite
  ga-> d ugrdprs
  Wrote 3801 of 3801 elements to grads.fwrite as Stream Little_Endian



  Mark Hess wrote:
  > All,
  >
  > I tried to search the GRADSUSR archives for the answer to this
  > question, but it gives me the error errno=146 "unable to initiate
  > communication...".  Perhaps you all can offer an answer.
  >
  > Does anyone have any sample strings for use with gradsdods to retreive
  > a GFS grib file from the NWS NCEP MOMANDS OpenDAP server?
  > (http://nomads.ncep.noaa.gov:9090/dods/gfs)
  >
  > I'm especially interested in how to extract data for a specified
  > geographical region.
  >
  > If anyone can get me started with this, I should be able to take an
  > example and work from there.
  >
  > Thank you.
  >
  > Mark
  >
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