McIDAS-XCD Administrator's Guide
Version 2021.1

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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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