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SYNOPSIS
gribtonc [-l logpath] [-v] [-t timeout] [-e errpath]
[-g userparams.tbl] [-q qspecs] [CDL_path]
netCDF_path
DESCRIPTION
This program decodes GRIB products (embedded in WMO prod
uct envelopes) on the NWS High-Resolution Data Service
(HRS) feed, writing the decoded products into a single
netCDF output file, specified by netCDF_path. In case the
output netCDF file does not already exist, the CDL_path
must be supplied to specify the structure for the desired
netCDF file, which gribtonc creates. The default parame
ter translation is made according to a definition by UCAR,
but the user may supply specific translations in a sepa
rate file by the -g tabfile option. The user-supplied
translations will override the default ones. GRIB prod
ucts are converted to the units specified for the appro
priate netCDF variable, if this differs from the units
used for the GRIB parameter. A set of CDL files for all
the model outputs appearing on the HRS data stream is pro
vided with gribtonc for use in decoding HRS GRIB data.
FORMAT OF GRIB TO NETCDF TRANSLATION TABLE
The format of the translation table is as follows: Each
line contains
GRIB parameter number
netCDF parameter name (cannot start with digit, [A-Za-z0-9_] only )
netCDF long description
netCDF units
An optional comment
These are all separated by semicolon (";"). To comment a
whole line, put any letter or special character (i.e. not
a digit) in front of it. Trailing spaces are ignored be
fore each semicolon, but not after. The GRIB number may
have spaces in front. Parameters found in the separate
file take presidence over the default parameter table,
those not listed in the separate file are unchanged. All
parameters will be named with a level suffix in addition
to the name assigned in the separate file.
EXAMPLE
The command
gribtocdl -v -g my.tab sst.grib > sst.cdl
will decode the products in sst.grib and generate the cor
responding CDL code into file sst.cdl. The file my.tab
contains a specific conversion table to be used when nam
ing a parameter from GRIB. Later the GRIB file may be
be used as a standalone decoder, decoding products on its
standard input into netCDF form, as specified by
netCDF_file GRIB products that do not conform to the spec
ified file structure (e.g. they are defined on a different
grid or contain a grid parameter not included in the spec
ified netCDF file) are skipped.
To use gribtonc from the LDM pqact(1) program requires
adding entries to the pqact configuration file that invoke
gribtonc on appropriate HRS products. The PIPE action
should be used in pattern-action entries. The form of
such an entry is:
HRS pattern PIPE gribtonc-executable
gribtonc-options
cdl-file netcdf-file
where pattern is a regular expression pattern matching
product identifiers of products that are to be decoded and
written to the output file netcdf-file.
Any directories that do not exist in netcdf-file will be
created as needed, so date components, for example, may be
part of the output file path, specified by using matched
parts of the regular expression pattern. In case the out
put netcdf-file does not already exist, it will be created
from the CDL specification in the file specified by cdl-
file.
The path of the executable for gribtonc must be specified
as the first argument to the PIPE command, and should be
either an absolute path name or in a directory in the exe
cutable search path of pqact.
An example pqact.conf entry for decoding GRIB products
from the ETA model as they appear on the HRS data stream
is:
# ETA model on Lambert conformal grid to yymmddhh_eta.nc
HRS ^Y.Q... KWBC (..)(..).*/mETA
PIPE /usr/local/ldm/decoders/gribtonc
etc/eta.cdl da
ta/GRIB/(1:yy)(1:mm)12_eta.nc
Since gribtonc reads GRIB products from its standard in
put, it may be invoked independently of pqact(1) by using
I/O redirection.
OPTIONS
-l logpath
Log file pathname. The program uses Unidata's
ulog(3) package to write error and log messages.
of the specified timeout, the program exits grace
fully.
-e errpath
If a GRIB product cannot be decoded, perhaps be
cause it is truncated or otherwise corrupted, it is
appended to this file.
-g tabfile
Use GRIB-netcdf translation defined in this file.
The format of this file is described below.
-q qspecs
Specification for how to expand so-called quasi-
regular or thinned grids into rectangular grids.
This argument is a comma-delimited text string that
specifies the method of interpolation used (cur
rently lin for linear or cub for cubic), and the
latitude and longitude increments in degrees for
the resulting grid (e.g. dlat=2.5,dlon=5.0).
CDL_path
The path name of a file to be used as a template
for the netCDF file, if the netCDF file specified
as output does not exist. If the netCDF output
file does exist, this argument is ignored. A path
name relative to the directory specified by the
LDM_ETCDIR environment variable may be used, but
you must make sure this environment variable is de
fined in gribtonc
netCDF_path
The path name of the netCDF output file. This may
be specified as an absolute path name or (more typ
ically) relative to the directory from which
gribtonc is invoked. Directories that do not exist
in the path name of the output file will be created
as needed.
EXAMPLE
The command
gribtonc -v -l- -q "lin,dlat=2.5,dlon=5.0" avn-x.cdl avn-x.nc < avn-x.wmo
will decode the products in avn-x.wmo into the netCDF file
avn-x.nc, creating the latter file if it does not already
exist from the ASCII CDL template file avn-x.cdl. If the
data contain quasi-regular grids, they will be expanded to
full regular grids on a 2.5 by 5.0 degree grid before be
ing written into the output file.
SEE ALSO
gribdump(1), netcdf(3), pqact(1), udunits(3), ulog(3)
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