[gembud] GRIB2 Data Unpacking in GEMPAK Files

• To: gembud@xxxxxxxxxxxxxxxx
• Subject: [gembud] GRIB2 Data Unpacking in GEMPAK Files
• From: Jeffrey Krob - NOAA Federal <jeffrey.a.krob@xxxxxxxx>
• Date: Tue, 28 Apr 2020 10:07:51 -0400

Hello,

I've been updating my display/diagnostic software (WINGRIDDS) to use GEMPAK
data files & it is working fine for the older versions of data files.
However, I'm having difficulties understanding the way GRIB2 data is
extracted for processing.

First off, with the GRIB2 decoding/ingest using 'dcgrib2' routine, I see
the decode_grib2 calls g2_getfld which uses the NCEP GRIB2 library routines
(g2_unpack1-7) to extract the data field & associated info. MDGRB2 gets set
and... the entire GRIB2 message (?) is passed to 'gb2_wgem' which
eventually gets to GD_WPG2 which looks like it writes it in the 'standard'
GEMPAK format.

HOWEVER...to read & use that data, the extracted GEMPAK data array (idata)
gets passed to 'DP_UGB2' then gets passed to 'GB2_UGEM'  which uses the
NCEP GRIB2 library routines (g2_unpack1-7) to extract the data field &
associated info...correct? This is where I get lost because I'm familiar
with the NCEP GRIB2 Libraries (I use them to decode GRIB2 data for use in
WINGRIDDS) but I can't make heads/tails of the data array even after
conversion from Integer to Character array). Is that a complete GRIB2
message - from 'GRIB -> 7777' or is it only portions?

Thanks in advance,
Jeff Krob
NOAA/NESDIS