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20010615: GRIB decoding in McIDAS



>From: Bill Fingerhut <address@hidden>
>Organization: Lyndon State
>Keywords: 200106111555.f5BFtJp07220 McIDAS XCD gribdec

Bill,

>I may be on the right track, but I have a few questions.

I think that it will be much easier for you if you use the gribdec.k
approach.  The ingesting of data into the HRS.SPL followed by running
of dmgrid.k (DMGRID) approach is simply much too hard in comparison
to gribdec.k

The first 7 questions are all related to the approach that we will not
be taking, so I will defer them to later _if_ you decide you still
want to pursue them (I don't think that this will happen).

>1. I assumed that everything is done within my account and not
>   ldm or mcidas? xcd decoding is installed and active all the
>   time, and I do not want to interfere with that.
>
>2. I understand the redirection change for GRID5*; what is the
>   role of HRS.SPL ?
>
>3. I made my own version of xcd_run in mcidas/data. It seems to do 
>   just 2 important things: set the environment and invoke ingebin.k   .
>   The environment seems easy enough. ingebin.k is in my path ; do
>   I need my own version of it?
>
>4. I was confused by LWU POKE GRIBDEC.PRO 4096 0
>   I can't find the file GRIBDEC.PRO  ?
>
>5. From mcidas/data  cat filename | ./xcd_run HRS  does the work.
>   Makes sense to me.
>   If I do this, I get an error related to file CIRCUIT.DAT; seems
>   like this is a good place to stop and get some help.
>
>6. Next is  DECINFO SET DMGRID A  
>   Is this right? Will this interfere with regular ingestion or does
>   it just affect what I am doing?
>
>7. DMGRID
>   Same type of question?

>Is this second method a better way to go?

Yes.  It is much easier.

>Down load from ??? Unidata ??? Must not be part of the distribution,
>however I have not looked for it.

gribdec.tar.Z is a set of code taken from the McIDAS distribution that
allows one to decode GRIB data (there are exceptions that are discussed
in a the file README.TXT that is contained in the distribution) outside
of the running XCD environment.  Since you are running XCD and you don't
want to intefer with its decoding, we use gribdec.

>I might need some help here since,
>'sigh' Mark isn't here anymore. We are on our own again until a 
>replacement is found. Is the download directory passworded?

The gribdec.tar.Z file can be gotten from the passworded McIDAS FTP
account:

machine: ftp.unidata.ucar.edu
user: umcidas
pass: XXXXXX
directory: unix/770/testcode
file: gribdec.tar.Z

Here are the instructions for building/using gribdec.k that are contained
in the README.TXT file that is contined in gribdec.tar.Z:

Build
-----

1. Create the directory $HOME/mcgribdec.

2. Copy the compressed tar file gribdec.tar.Z to $HOME/mcgribdec.

3. Uncompress and extract the tar file.

        cd $HOME/mcgribdec
        zcat gribdec.tar.Z | tar -xf -

4. Edit the Makefile and set the MCROOT macro to the home directory of the
   McIDAS account on your workstation.

5. Create the following directories if they don't already exist

          mkdir $HOME/mcidas/bin
          mkdir $HOME/mcidas/data
          mkdir $HOME/mcidas/help

6. Verify that your PATH environment variable includes the ~mcidas/bin
   directory.

7. Run 'make'.  The gribdec.k executable will be placed in the directory
   $HOME/mcidas/bin and various data files will be placed in $HOME/mcidas/data.


README.TXT also contains the information to run gribdec.k:

Running GRIBDEC
---------------

Make sure your MCPATH environment variable includes $HOME/mcidas/data so
that GRIBDEC can find the necessary data files.

Synopsis.

   GRIBDEC <file> <gridfile> <'Grid File Title'>

        FIRSTBYTE=    Byte to begin reading from file (def=1)
        NUM=    Number GRIB message to process (def=999999)

   where:

      file      - The name of the file containing the GRIB messages.
        gridfile - Grid file number to file decoded grids
        'Grid File Title' - Title to call grid file.

When running gribdec.k from the Unix command line, the invocation syntax
will be:

gribdec.k <file> <gridfile> <'Grid File Title'>

Give the download a try and let me know if you run into any snags building
the gribdec.k executable.

Tom


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