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Re: decoders] First post - GRIB2 decoders




Jelle,

i forget to mention there is way to convert the file to netCDF without doing any coding.

url: http://www.unidata.ucar.edu/software/decoders/grib2netcdf

robb...





On Wed, 20 Feb 2008, Jelle Ferwerda wrote:


Hi Robb,

Thanks so much for your reply.

I realize that the Grib2 decoder is not intended for batch-decoding. That being said.. I am afraid it is the only thing that gets close enough at the moment for me. Also: The MPE files are quite small (2Mb), have only one grid, and I can -after decompressing- straight away subset it for my ROI (Which is only central kenya) and store them as one spatial archive files (e.g., HDF) for each day or season.

If you do have time and could have a peek (& possible whip a few lines of code up that could help me decode a file in a more generally supported filetype?), that would be amazing! The link for the datafiles is: http://oiswww.eumetsat.int/~idds/html/grib.html. I normally work in IDL/ENVI, which supports aot the NETCDF format, which I think is the data-backbone of the UCAR library? Or I might just look into running the java decode as part of an IDL data processing stream, whichever is easier to manage. Eventually I expect to just run the program once or twice a month on updated files, and retrieve the data for my AOI, archive the .grb files on the data archiver, and export a composite of the new data to my analysis machine. Just so have some idea of what I have been trying so far, I have attached the java file I was working on for the past few days, trying to implement the unidata java class. As you can see: My java skills are not very good...

Thanks so much!

Jelle.


Jelle,

The Grib2 decoder isn't a batch file decoder for getting data. The idea is to make an index for the file using Grib2Indexer <fileName> and to use the Index to find what parameter to actually decode the requested parameter
 data. The design was the result of very large Grib files.

% Grib2Dump <fileName>  shows the metadata of each record.
% Grib2Indexer <fileName>  gives the index of the file
The file IndexFormat.txt in the root of the distribution explains the details of a Grib index. sample line:

0 0 0 6 2 103 2.0 255 0.0 2008-02-11T14:00:00Z 0 -418705429 121261 121342

% Grib2GetData <fileName> <GDS offset> <PDS offset> gets the data for record

from above sample index line:

% Grib2GetData <fileName> 121261 121342

Don't forget to set the CLASSPATH variable to the jar file.

I'll download a test file to see if there are any problems decoding this type of data.

Robb...



Exception in thread "main" java.lang.NegativeArraySizeException
at ucar.grib.grib2.Grib2GridDefinitionSection.<init>(Grib2GridDefinitionSection.java:300)
      at exportgrb.Main.main(Main.java:71)


// Some code

   // Paths and stuff
   String InFile          = "c:\\java\\data\\MPE_20080217_0900_M9_00.grb";
   Boolean CheckTheSum = true;

  // Create a unidata specified RandomAccesFile for reading
ucar.unidata.io.RandomAccessFile InRA = new ucar.unidata.io.RandomAccessFile(InFile, "r");

  // Grid definition section
Grib2GridDefinitionSection GDSd = new Grib2GridDefinitionSection(InRA, CheckTheSum);
    String GGdef = GDSd.getGridName(0);
    System.out.println(GGdef);

// -- end some code

I hope that someone can help me and explain how to fix this. Or even better: Is there someone who has already created a decoder specifically for the multisensor precipitation estimates?

Thanks so much,

Kind Regards,

Jelle Ferwerda

-----------------------------------------------
Jelle Ferwerda
Postdoctoral Research Fellow

Animal Behavior Research Group
Department of Zoology / University of Oxford
South Parks Road / Oxford / OX13PS
United Kingdom

email:         address@hidden
Office Phone:     +44 18652 71214
WWW:        http://www.bio-vision.nl
-----------------------------------------------


--

-----------------------------------------------
Jelle Ferwerda
Postdoctoral Research Fellow

Animal Behavior Research Group
Department of Zoology / University of Oxford
South Parks Road / Oxford / OX13PS
United Kingdom

email:         address@hidden
Office Phone:     +44 18652 71214
WWW:        http://www.bio-vision.nl
-----------------------------------------------
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=============================================================================== Robb Kambic Unidata Program Center
Software Engineer III               Univ. Corp for Atmospheric Research
address@hidden           WWW: http://www.unidata.ucar.edu/
===============================================================================

--

-----------------------------------------------
Jelle Ferwerda
Postdoctoral Research Fellow

Animal Behavior Research Group
Department of Zoology / University of Oxford
South Parks Road / Oxford / OX13PS
United Kingdom

email:          address@hidden
Office Phone:   +44 18652 71214
WWW:            http://www.bio-vision.nl
-----------------------------------------------


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