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Re: [netcdf-java] Missing GRIB parameters in NetCDF?

  • To: Tor Christian Bekkvik <torc@xxxxxx>
  • Subject: Re: [netcdf-java] Missing GRIB parameters in NetCDF?
  • From: Robb Kambic <rkambic@xxxxxxxxxxxxxxxx>
  • Date: Thu, 20 Aug 2009 11:32:42 -0600 (MDT)
On Thu, 20 Aug 2009, Tor Christian Bekkvik wrote:



Hi,
I am using NetCDF to read GRIB/GRIB2 files. Almost everything works fine, but
some GRIB parameters seems to be unavailable via the NetCDF API. I this case,
I could not find
       "RESOLUTION AND COMPONENT FLAGS (GDS OCTET 17)" from the GRIB file.
, at least not in the NetCDF attributes..

(Details: This GDS parameter from the GRIB file tells how to interpret
direction from combined U- and V- components. (In my case, current vectors from
weather data)
Text from GRIB standards documentation:

      TABLE 7 - RESOLUTION AND COMPONENT FLAGS (GDS OCTET 17):
      Bit 5:
      0     u- and v-components of vector quantities resolved relative
              to easterly and northerly directions

      1     u and v components of vector quantities resolved relative
              to the defined grid in the direction of increasing x and y
              (or i and j) coordinates respectively

)

 

- How could we get this GRIB parameter ?




Tor,
The information is already available, it's designated as the winds attribute. This is available in 6.x and 7.x index versions. 

String winds = GribNumbers.isBitSet(gdsv.getResolution(),
GribNumbers.BIT_5)
                       ? "Relative"
                       : "True";


There has been a major refactor of the grib library, the GridDefRecord
class has both  RESOLUTION AND COMPONENT Flags and the Winds attribute
available. The new library has a slightly different API in the index that makes available all the information that resides in the PDS and GDS sections of the Grib file. 

The new package is available from the decoders web page at:

http://www.unidata.ucar.edu/software/decoders/

The latest version is 8.1
The older index code has been deprecated and those classes will be removed in future releases. 


Robb....


 

Thanks,

Tor Chr Bekkvik

 

 

 





===============================================================================
Robb Kambic                                Unidata Program Center
Software Engineer III                      Univ. Corp for Atmospheric Research
rkambic@xxxxxxxxxxxxxxxx                   WWW: http://www.unidata.ucar.edu/
===============================================================================
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