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HOME > Monitoring_and_Data > Oceanic and Atmospheric Data > Reanalysis: Atmospheric Data > wgrib2-geolocation

wgrib2: -geolocation


Geolocation routines are used to calculate the longitudes and latitudes of the grid points. Wgrib2 can use Proj4, gctpc and its own internal routines to do the geolocation. Each set of routines has advanages and disadvantages. The routines are listed in the default order.


Proj4 is the gold standard of geolocation libraries. It is commonly used and well supported. The drawbacks are it doesn't support OpenMP and model grids. By default, Proj4 is not installed into wgrib2. It's main use is to confirm that the faster gctpc is working. Without OpenMP support, speed is a major problem.


Gctpc is an older library which has lost support of its original authors (USGS). The advantage is that it does support OpenMP unlike Proj4. It supports fewer grids than Proj4 but that isn't a major problem because the grib2 standard only has support for a few grids. Gctpc supports an ellipsoidal earth and is always compiled with wgrib2.


The internal routines only support a spherical earth. Its main use is to support various model grids such as Gaussian grid, and rotated lat-lon grid. The internal routines are also used by various observational grids such as the space-view grid (used by EUMETSAT) and radar grids (angle, distance from the origin).


    print out geolocation routines used: proj4, gctpc, internal, or not_used
    If wgrib2 does not need the geolocation information, the geolocation routines
     will not be called. 


$ wgrib2 burned_area_20120131_12_23_1km.grib2 -geolocation -lon -90 30  -d 1
1:0:d=2012013123:FBAREA:no_level:anl:Sat -1 -1 Ins 1 9e+19 m-1 :gctpc:lon=270.004694,lat=29.997210,val=0

    gctpc routines were used for geolocation

$ wgrib2 burned_area_20120131_12_23_1km.grib2 -geolocation -d 1
1:0:d=2012013123:FBAREA:no_level:anl:Sat -1 -1 Ins 1 9e+19 m-1 :not_used

    The options did not request geolocation.
See also: -gctpc -proj4

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