Introduction

wgrib2 is not simple upgrade of wgrib for grib-2 files. wgrib can slice and dice grib-1 files. wgrib2 is more like four drawers of kitchen utensils as well as the microwave and blender. This kitchen miracle was done by a more developer friendly design and the contributions of many people.

• inventory and read grib-2 files (grib-1 is not supported)
• manipulate (reorder, extract) grib-2 records (messages)
• ieee, text, binary, comma separated values (CSV) output
• extract data for specified latitude/longitudes
• conversion to netcdf-3, netcdf-4 (optional package)
• export to a mysql database (optional package)
• script-level parallel program possible
• regional subsets
• interpolate to new grid (-new_grid, optional package)
• change grid-relative winds to earth relative winds (-new_grid, optional package)
• creating new grib-2 files
• parallel processing by using threads (OpenMP)
• support for flow-based programming

Grib-1 versus Grib-2

GRIB-2 has arrived and has begun replacing the the older standard GRIB (GRIB-1). Since GRIB-2 can reduce the file size by upto 80% (NAM, JPEG2000 compression), converting to the new standard may be faster than some expected.

Sometimes you want to use a feature of wgrib2 on a grib-1 file. Since wgrib2 doesn't do grib-1, you are out of luck unless you convert the file into grib-2. Some files can be converted into grib2 by the cnvgrib utility.

News

8/2009: Recommended that you update to v1.8.1, v1.8.0 and v1.8.1 added bug fixes to core routines.
Can now create new complex packed files, and have converted a GrADS readable file (HDF) into grib-2.

5/2008: mysql support, thanks Niklas Sondell
custom regional grids, write your own grib files

3/2008: Recommended that you update to v1.7.1 as this version fixes a bug with the old-style -i option and has a much faster -grib option.

1/2008: Updated grib tables, updated netcdf, added a grib2 output routine

Kristian Nilssen has sent in a module to write netcdf files. Compiled cleanly and converted grib2 into netcdf. Will be released as an alpha option because the output format may change.

Sergey Varlamov has improved the netcdf module to add multiple output times.

2/2007: Manfred Schwarb went over the code last Christmas-New Years and sent in 31 patches. 31 patches sounds like a lot but he must have used a spell checker on the code. Anyways some of the patches were for the more unpolished code in the package which caused me to go over that code. Manfred also sent in a script that can read a grib2 table from the web documentation and create C code. Much better than typing by hand or any other script that I had in my tool box.

9/16/2005 alpha version is released to the public.

Some Good Stuff

• Almost trivial to add custom features!
• Customized inventories
• Table driven
• Code is reorganized
• Super easy integration of new and local options
• wgrib2 knows the lat-lon of the individual grid points for several grids
• Works with the partial-http downloading aka "Fast Downloading of GRIB Files"

Bad Stuff

• Uses external libraries (png,jpeg,netcdf,compression,grib2 decode,interpolation) which can make compiling and linking a real pain.
• interpolation to lat-lon values is done by nearest neighbor except when using -new_grid
• wind rotation is not handled except when using -new_grid
• -new_grid is part of the optional IPOLATES package

Usage

• similar to wgrib but different
• each option call corresponds to a subroutine call
• type wgrib2 to see primary options
• inventory format is specified on command line by options
• if no "inv" option is specified, -s is used

Joining the development effort

• Source code: knowledge of C and some grib-2
• Donated source code / non-trivial bug fixes must either be GNU or public domain.
• Prefer PD bug fixes for PD code and GNU bug fixes for GNU code.
• Bug reports are important
• Contact wesley.ebisuzaki@noaa.gov

Contributions by

• Wesley Ebisuzai: many modules
• Reinoud Bokhorst: tosubmsg, checksum
• Jaakko Hyvätti: gribtab
• Kristian Nilssen: netcdf module
• Karl Pfeiffer: georeference
• Pablo Romero: unix_time
• Manfred Schwarb: many modules
• Arlindo da Silva: openGrADS, bbox
• Niklas Sondell: mysql module
• Sergey Varlamov: netcdf module improvements, georeferencing updates
• thanks to the people who report the bugs and more who provide the fixes!

Documentation

• intro_grib2.pdf using GFS fcst
• Understanding the default inventory
• converting from wgrib to wgrib2 in scripts
• Powerpoint presentation 4/6/2011 at NCEP
• submessages
• writing a simple function
• selecting fields to decode
• option types: init inv out misc
• bin, ieee, text format
• small fast databases
• usage questions
• using pipes and multiprocessing
• compile questions
• limitations
• make wgrib2 faster
• calling wgrib2 from C
• some tricks

The options

• the common options
• all the commands

Selecting Fields/Records/Message

Select/Ignore by name/level/time/etc

• -match process records that match a posix extended regular expression
• -not process records not matching a regular expression
• -match_inv the inventory used by -match and -not
• -i reads inventory from stdin for record selection

Select by number (better to use previous method)

• -d dump specific record
• -for select a range of records to process (nth message)
• -for_n select a range of records to process (nth message/submessage)

Selective Processing: if options

After selecting the fields to process, you can refine the processing by the "if" options. For example, you selected the winds and temperatures. You can use the "if" to send the winds to one file and the temperatures to another file. In general it is faster to use the -match/-not options because there is less processing of the data.

• -if if this then that
• -not_if if not this then that
• -fi closes -if (often an output option closes the if)

Individual Grid Point Data

• -ij print value at grid point (i, j)
• -ijlat print lat, lon, value at grid point (i, j)
• -ilat print lat, lon, value of Nth grid point
• -lon prints the lat-lon, and value of the grid point nearest the specified lat-lon
• -max prints the maximum value
• -min prints the minimum value
• -stats prints some statistics about the fields
• -V verbose inventory (shows stats)

Regridding, Interpolating to new grids

Wgrib2 has the ability to convert grib files from one grid to another. The conversion uses a user-selected interpolation scheme: bilinear (default), bicubic, nearest neighbor and budget. The supported grids (7/2010) include lat-lon, gaussian, Lambert conformal and polar stereographic. This capability uses the NCEP IPOLATES library and is an optional package.

Note: the interpolation uses scalar and vector interpolation schemes. For the vector quantities the V field must immediately follow the corresponding U field.

• new_grid
• -new_grid_interpolation set interpolation type used by -new_grid BETA

Modifying grid data

• set grid points to undefined based on region
• set grid points to undefined based on value
• Change units, useful for making CSV files
• Compute new fields
  • thickness
  • find max/min/ave value in a time series
  • wind speed/direction
• Convert binary data to grib2
• Convert GrADS compatible data data to grib2 (g2grb.gs)
• Merge subregions; i.e., combine tiles

sh-3.00$ wgrib2 rtgssthr_grb_0.083_awips.grib2 -V
Segmentation fault

-sh-3.00$ ulimit -s 30000
-sh-3.00$ wgrib2 rtgssthr_grb_0.083_awips.grib2 -V
1:0:vt=2009062900:surface:anl:TMP Temperature [K]:
    ndata=9331200:undef=3246169:mean=287.003:min=271.33:max=312.8
    grid_template=0:
        lat-lon grid:(4320 x 2160) units 1e-06 input WE:NS output WE:SN res 48
        lat 89.958000 to -89.958000 by 0.083000
        lon 0.042000 to 359.958000 by 0.083000 #points=9331200

bash-3.2$ wgrib2 gfs.t00z.sfluxgrbf06.grib2 -match "GRD:10" -new_grid_winds earth -set_grib_type c2 -new_grid latlon 0:3600:.1 -90:1801:.1 junk.grb2
36.1:23114245:d=2011111700:UGRD:10 m above ground:6 hour fcst:
Segmentation fault

bash-3.2$  ulimit -s 4400000
bash-3.2$  wgrib2 gfs.t00z.sfluxgrbf06.grib2 -match "GRD:10" -new_grid_winds earth -set_grib_type c2 -new_grid latlon 0:3600:.1 -90:1801:.1 junk.grb2
36.1:23114245:d=2011111700:UGRD:10 m above ground:6 hour fcst:
36.2:23114245:d=2011111700:VGRD:10 m above ground:6 hour fcst:
112.1:63622055:d=2011111700:UGRD:10 m above ground:0-6 hour ave fcst:
112.2:63622055:d=2011111700:VGRD:10 m above ground:0-6 hour ave fcst: