Converting GRIB codes

For users to understand GRIB messages, the decoder must change portions of them into meteorological values. For example, a value of 11 in the ninth byte of the PDS is meaningless until it is converted to temperature in degrees Kelvin. Other attributes that must be converted include the geographic location, the forecast time units, and the generating model name and originating location.

GRIB1

Currently, five types of ASCII file lookup tables are included with the McIDAS-XCD GRIB1 decoder for this purpose. These files are found in ~mcidas/data and begin with the characters gbtbpds as shown below.

Attribute	Section/Byte	Files
processing center	PDS/5	gbtbpds001.0v1
parameter/unit	PDS/9	gbtbpds001.2v1, gbtbpds001.2v2, gbtbpds001.2v3, gbtbpds001.2v131
forecast time	PDS/18	gbtbpds001.4v1
model	PDS/6	gbtbpds001.av1, gbtbpds001.a34v1, gbtbpds001.a60v1, gbtbpds001.a74v1, gbtbpds001.a98v1
geographic location	PDS/7	gbtbpds001.bv1, gbtbpds001.b98v1

When the decoder finds a value for one of these attributes, it checks the appropriate lookup table for information about the value. If it cannot find the information, the message is discarded.

GRIB2

Three ASCII file lookup tables are included with the McIDAS-XCD GRIB2 decoder for this purpose. These files are found in ~mcidas/data and begin with the characters grib2 as shown below.

Attribute	File
geographic location	grib2NavLookup.txt
parameter/unit	grib2Parameters.txt
model	grib2NCEPModels.txt

The McIDAS-XCD GRIB2NAV command lists McIDAS navigation values that can be added to grib2NavLookup.txt. See Configuring Additional GRIB2 ADDE Datasets for more information.

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