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The Grib1 reader uses a Table based on the site ID, sub-site ID, and version number from the data to read in a particular Table while Grib2 only has one parameter table. Sometimes there is a need to add/overwrite Grib1 tables or to add/overwrite Grib2 parameters for the Grib Library. This process is not difficult.
First one needs to create a file listing the new tables, the file has the following syntax of site ID, sub-site ID, version number, and table name each separated by a :. The -1 is a wild card character and it match any number in the field. If the table name begins with /, http:, or file: then the table is loaded with the full path name, otherwise the table is assumed to be in the resources/grib/tables directory in the Grib package or jar. Here is a sample table file configuration.
7: -1: 0: nceptab_2.tab 7: -1: 1: nceptab_1.tab 7: -1: 2: nceptab_2.tab 7: -1: 3: nceptab_3.tab 158: 0: 2: /grib/tables/fnmoc_2.tab
The routine GribPDSParamTable.addParameterUserLookup(String userGribTabList) reads the above configuration file.
The newly created tables must be in NCEP format of parameter number, short name, long name and units inside []. The fields are separated by :. Here is a sample Grib1 table, the first line always starts with -1 : site ID : sub-site ID : version number. The -1 is a wild card character, same as above.
-1:7:-1:2 0:var0:undefined 1:PRES:Pressure [Pa] 2:PRMSL:Pressure reduced to MSL [Pa] 3:PTEND:Pressure tendency [Pa s-1]
Remember if one is overwritting a table then only the new table parameters will be available.
Since there is only one Grib2 table, there is no need for the table configuration file as in Grib1. The only file needed is a file that contains the parameters that need to be add/overwritten. This file has the following syntax:
# Sample Grib2 table parameters that are read in externally # Use static method: ParameterTable.addParametersUser(String UserGribTable) # Grib 2 Table: http://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_table4-1.shtml # The fields are separated by tabs, Name cannot have spaces, use _ # fields: # Discipline Category ParameterNumber Name Unit Description 0 1 223 Total_precipitation kg/m2 Total precipitation in 24 hours 0 2 1 Wind_speed knots Wind speed at 2 metersThe routine ParameterTable.addParametersUser("C:/data/grib/tables/grib2userparameters.txt" ); reads in the above parameters.
Only the parameters with the Discipline Category ParameterNumber are modified, the other parameters remain unchanged. Remember the fields must be separated by tabs and the field definitions can be obtained at: Grib 2 Table Information
Parameters can be loaded at runtime by a configuration file described at RuntimeLoading
If there are questions about adding/overwriting tables/parameters, create a support ticket at: support netcdf-decoders
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