[netcdf-java] GRIB v2 files

• To: <netcdf-java@xxxxxxxxxxxxxxxx>
• Subject: [netcdf-java] GRIB v2 files
• From: "Comiskey, Glenn" <g.comiskey@xxxxxxxx>
• Date: Fri, 17 Jun 2011 12:27:52 +0100

Hi,
 
Have an issue with publishing GRIB v2 datasets via ERDDAP which my
current understanding is due to a way NetCDF-Java reads GRIB v2 files.
 
Had set-up a Tomcat v6.0.32/ERDDAP v1.28 server on Windows and run the
GenerateDatasetsXml.bat to generate the XML for inclusion into
datasets.xml. Specified option EDDGridFromNcFiles and pointed it to a
forcast GRIB v2 file with records WIND, WDIR, UGRD, VGRD, HTSGW, PERPW,
DIRPW, WVHGT, SWELL (1 in sequence), SWELL (2 in sequence), WVPER, SWPER
(1 in sequence), SWPER (2 in sequence), WVDIR, SWDIR (1 in sequence),
SWDIR (2 in sequence) for every 3 hours 0 - 180 from reference time.
GenerateDatasetsXml.bat, which I understand uses NetCDF-Java to read the
file, recognised the dimensions time, lat, lon and therefore reported
data variables for WIND, WDIR, UGRD, VGRD, HTSGW, PERPW, DIRPW, WVHGT,
WVPER, WVDIR without any problem, but only reported a single data
variable for SWELL (1 in sequence), SWELL (2 in sequence) and similarly
for SWPER and SWDIR (which when accessing the data via ERDDAP appeared
to relate to the "2 in sequence" record), i.e. it was only possible to
access GRIB v2 records SWELL (2 in sequence), SWPER (2 in sequence) and
SWDIR (2 in sequence).
 
However, having set-up a Tomcat v6.0.32/ERDDAP v1.32 server on Windows
and run GenerateDatasetsXml.bat on the same GRIB v2 file and selected
option EDDGridFromNcFiles it now appears to recognise dimensions time,
ordered_sequence_of_data, lat, lon, and as a result only reports data
variables SWELL, SWPER and SWDIR due to the fact that they are the only
one that share the recognised dimesions - which is a requirement of
ERDDAP.
 
Given my understanding of how GRIB v2 files are constructed, and how
that data is meant to be interpeted, I am expecting
GenerateDatasetsXml.bat to generate XML entries for three dimensions
(time, lat, lon) and data variables for all 16 records; with SWELL (1 in
sequence) and SWELL (2 in sequence) being distinctly seperate data
variables as with SWPER and SWDIR. This is to say that for any given
location (lat, lon) and forcast time, or time period, then SWELL (1 in
sequence) and SWELL (2 in sequence) etc. should be reported.
 
Why is it that NetCDF-Java does not appear to be able to understand that
a GRIB v2 file can have records that have common dimensions and
distinctly seperate data variables that represent that same data type.
 
Kind regards,
 
Glenn Comiskey
Data System Administrator
 
Fugro Global Environment & Ocean Sciences
Fugro House, Hithercroft Road
Wallingford, Oxfordshire OX10 9RB, UK
Registration No: 2985431 / VAT No: GB 655475606
 
Tel: +44 (0) 1491 820500 (Switchboard) / Tel: +44 (0) 1491 820559
(Direct) / Fax: +44 (0) 1491 820599
E-mail: g.comiskey@xxxxxxxx <mailto:g.comiskey@g.comiskey@xxxxxxxx>  /
Website: www.geos.com <http://www.geos.com/> 
 
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• Follow-Ups:
  • Re: [netcdf-java] GRIB v2 files
    • From: John Caron
  • Re: [netcdf-java] GRIB v2 files
    • From: John Caron