Re: [netcdf-java] GRIB v2 files

Hi Glenn:

If you can send me the problem file, id like to examine it before I try to guess.


On 6/17/2011 5:27 AM, Comiskey, Glenn wrote:
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
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