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Step-by-step guide

Local tables for parameters

A common candidate for local adaptation is the handling of local parameters. The standard parameter descriptions are contained in the files name.def, paramId.def, shortName.def and units.def in directories:

/usr/local/share/eccodes/definitions/grib[edition]

The parameter descriptions for a given centre are contained in the directories:

/usr/local/share/eccodes/definitions/grib[edition]/localConcepts/[centre:s]

So for example the GRIB edition 2 local parameters for DWD (centre=edzw) are defined in definitions/grib2/localConcepts/edzw and GRIB edition 1 local parameters for SMHI (centre=eswi) are in definitions/grib1/localConcepts/eswi.

The following in an example of the contents for the above files in order to handle ECMWF parameter Geopotential in GRIB edition 1:

#Geopotential
'Geopotential' = {
    table2Version = 128 ;
    indicatorOfParameter = 129 ;
}

#Geopotential
'129' = {
    table2Version = 128 ;
    indicatorOfParameter = 129 ;
}

#Geopotential
'z' = {
    table2Version = 128 ;
    indicatorOfParameter = 129 ;
}

#Geopotential
'm**2 s**-2' = {
    table2Version = 128 ;
    indicatorOfParameter = 129 ;
}

And for GRIB edition 2, the contents of the same files for parameter Potential temperature gradient are:

#Potential temperature gradient
'Potential temperature gradient' = {
    discipline = 192 ;
    parameterCategory = 129 ;
    parameterNumber = 3 ;
}

#Potential temperature gradient
'129003' = {
    discipline = 192 ;
    parameterCategory = 129 ;
    parameterNumber = 3 ;
}

#Potential temperature gradient
'ptgrd' = {
    discipline = 192 ;
    parameterCategory = 129 ;
    parameterNumber = 3 ;
}

#Potential temperature gradient
'K' = {
    discipline = 192 ;
    parameterCategory = 129 ;
    parameterNumber = 3 ;
}

Local Definitions (Local Use section)

Local definitions are also required when one needs to store information which is not part of the standard GRIB header. This would typically be a mars MARS key (like class, stream, type and version number or experiment identifier, expver) or information that the data producer wants to have in each GRIB for convenience.

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codetable[1] marsClass   "mars/class.table" = "od" : dump,lowercase;
codetable[1] marsType    "mars/type.table" = "an" : dump,string_type,lowercase;
codetable[2] marsStream  "mars/stream.table" = "oper" : dump,lowercase ;
ksec1expver[4] experimentVersionNumber = "0001" : dump;

alias mars.class  = marsClass;
alias mars.type   = marsType;
alias mars.stream = marsStream;
alias mars.expver = experimentVersionNumber;

Example of a GRIB2 local definition

Suppose we want to add a GRIB2 local definition for a given centre (let's say code 87). The local definition will have some integer keys and a string key.
So first we create the file "grib2LocalSectionNumber.87.table" and place it in the definitions/grib2 directory. This is a codetable with codes for the local definition numbers and a brief description.

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Here we assign 2 bytes to the myVersion field (a positive integer), 10 bytes to the ASCII character string myName and 1 byte to the final myNumber integer.

Creating your own tables

Sites can create their own tables in order to adapt ecCodes to their needs. The clear candidates for site specific tables are:

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# GRIBcode   Acronym    Long name
1001         eebc       Ensemble using ECMWF data as Boundary Conditions
1002         eeic       Ensemble using ECMWF data as Initial Conditions

Another candidate for local adaptation is the handling of local parameters. The standard parameter descriptions are contained in the files name.def, paramId.def, shortName.def and units.def in directories:

/usr/local/share/eccodes/definitions/grib[edition]

The parameter descriptions for a given centre are contained in the files directories:

/usr/local/share/eccodes/definitions/grib[edition]/localConcepts/[centre:s]

The following are examples of the contents for the above files in order to handle ECMWF parameter Geopotential in GRIB edition 1:

#Geopotential
'Geopotential' = {
         table2Version = 128 ;
         indicatorOfParameter = 129 ;
        }

 #Geopotential
'129' = {
         table2Version = 128 ;
         indicatorOfParameter = 129 ;
        }

#Geopotential
'z' = {
         table2Version = 128 ;
         indicatorOfParameter = 129 ;
        } 

#Geopotential
'm**2 s**-2' = {
         table2Version = 128 ;
         indicatorOfParameter = 129 ;
        }

In GRIB edition 2, the contents of the same files for parameter Geopotential are:

#Geopotential
'Geopotential' = {
         discipline = 0 ;
         parameterCategory = 3 ;
         parameterNumber = 4 ;
        }

 #Geopotential
'129' = {
         discipline = 0 ;
         parameterCategory = 3 ;
         parameterNumber = 4 ;
        }

#Geopotential
'z' = {
         discipline = 0 ;
         parameterCategory = 3 ;
         parameterNumber = 4 ;
        }

#Geopotential
'm**2 s**-2' = {
         discipline = 0 ;
         parameterCategory = 3 ;
         parameterNumber = 4 ;
        }

Install and test your changes

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Also please study the slides here:  Training course presentation.
And the How-To Article GRIB: Converting edition 1 to 2 (The "Local configuration" section)

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