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20020131: dcgrib2 packing

Clint,

Dcgrib2 uses grib packing. For eta211, where no stitching
together of grids and/or thickening/flipping is needed,
the GRIB BDS section is just written to the GEMPAK file without 
any modification and the header information is updated. The number of bits
used will be dependent on each parameter as specified in the grib
product, rather than one value for the entire data set.

Your problem with GDMOD is that the grid is unpacked when read
in, then repacked when written out. So, for grids using less than
16 bits, they will then be larger.

I don't see anyway to move a grid n GDMOD without unpacking.

Steve Chiswell




>From: Clint Rowe <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200201311853.g0VIr7x24388

>Chiz,
>
>What's the default packing scheme used by dcgrib2?  Is it hardcoded or
>is it specified in a table somewhere?
>
>I wanted to add some diagnostic grids (on a regular basis) to the eta211
>but I didn't have MAXGRD set large enough.  So, I ran gdcfil to create
>a new grid file with a bigger header, then ran gdmod to copy all the grids
>from the old eta211 to this file.  When I specify gpack=grib/16, the
>resulting file is nearly twice as large as the one made by dcgrib2, but if
>I set gpack=grib/8, it's smaller -- even though the header's bigger.  I
>tried to look through the support archives and the code, but got too 
>frustrated, since it should be a one-shot problem.  I've already set
>the maxgrd parameter in gribkey.tbl so they'll be room in the future, but
>I wanted to test my script.
>
>Clint
>
>====================================================================
>Clinton M. Rowe
>Associate Professor 
>Meteorology/Climatology Program                  phone:(402)472-1946
>Department of Geosciences                          fax:(402)472-4917
>University of Nebraska-Lincoln                        address@hidden
>
>