wgrib2: -set_ext_name
Introduction
In the beginning, grib fields were identified by a name, a level
and some timing information. Life was simple and the people were
happy. This was soon to pass. A hoard of ensemble members appeared
in the distance. A dust storm rolled in from the plains. The new
power plants started putting sulfar dioxide into the air. All this
had to added to the grib format. So names had to have modifiers,
the percentile of some particulates of some chemical between size
A and B microns. So wgrib2 added "extended names".
So you could switch beween the old simpler names and the newer extended names.
Why would you want use extended names? Sometimes you want the names to
be unique. For example, when creating NetCDF file, you want the TMP from
ensemble member 1 to has a different name from ensemble member 2. In another
example, you may want to search for a unique field. With the extended name,
you only need simple name comparison.
Extended Names
The extended name includes modifiers like the ensemble information,
dust information and probabilities. Optionally you can include
the level and forecast information (wgrib2 v3.0.2+). More details
are given here.
Usage
To select between the regular and extended name, you use
-set_ens_name N
N == 0 default
N == 1 add misc terms like ensemble or probability
extension for wgrib2 v3.0.2+
and(N,1) == 1 add misc terms like ensemble or probability
and(N,2) == 2 add level information
and(N,4) == 4 add forecast information
ex N == 3 misc + level information
ex N == 5 misc + forecast information
ex N == 6 level information + forecast information
ex N == 7 misc + level information + forecast information
N > 7 for future use
Extended Extended Names
The extended name facility was extended with wgrib2 v3.0.2 in order
to fix a problem with converting grib to netcdf with some of the newer
NCEP files. When wgrib2 writes netcdf files, the -netcdf concatinates
the level information to the extended name to produce the netcdf name
for the field. For some of the newer NCEP forecast files, this name
wasn't unique. So the extended name needs to optionally include
the forecast time information. With this extension, the level
information was added as another option field to the extended name.
$ wgrib2.v3.0.2 FCST.grb -set_ext_num 1 -netcdf FCST.nc
lost fields because the field names were not unque
$ wgrib2.v3.0.2 FCST.grb -set_ext_num 5 -netcdf FCST.nc
extended name include misc-info and forecast-time-info.
The final modification to the extended name, was to make the field and space
character a run-time parameter by the option, -set_ext_name_chars. The default
values are '.' and '_' for backwards compatibilty. The modification was needed
we now are seeing level-info and misc-info with periods in them like "0.5 mb".
-match, -if, and other string matches
The extended names also applies the match inventory. So string matches will have
to be rewritten. Fortunately the process is mechanical.
-match ":RH:" -> -match ":RH(:|.)"
-match ":RH:500 mb:" -> -match ":RH(:|.)" -match ":500 mb:"
Many options use the extended name if enabled by -set_ext_name. For example, the
-netcdf uses the extended name if enabled.
Examples
-sh-2.05b$ ./wgrib2 chem.grb2 -var
1:0:MASSDEN
-sh-2.05b$ ./wgrib2 chem.grb2 -ext_name
1:0:MASSDEN.hi-res_ctl.Water_Vapour
-sh-2.05b$ ./wgrib2 chem.grb2 -set_ext_name 1 -ext_name
1:0:MASSDEN.hi-res_ctl.Water_Vapour
See also:
-ext_name
-set_ext_name_chars.
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