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HOME > Monitoring_and_Data > Oceanic and Atmospheric Data > Reanalysis: Atmospheric Data > wgrib2-ll2i

wgrib2: -ll2i


The -ll2i and -ll2ij options are in alpha status.

The -ll2i has been redefined (v2.0.5) so that it returns the value 1..ndata. This change was to support grids from 1..2^32 - 1 grid points. With this change, 0 denotes a lat-lon that is outside of the domain.

The -lon option uses a brute-force method to find the closest grid point to a specified latitude and longitude. It finds the minimum distance to each grid point. This slow procedure is more-or-less necessary when your geolocation routines can transfrom from (X,Y) -> (lon, lat) but not (lon, lat) -> (X, Y). The gctpc/Proj4 geolocation libraries have both the forward and inverse transformation so improved geolocation routines can be added to wgrib2 such as a fast -lon option and a bilinear interpolation option.

Some grids only have an (i,j) -> (lon,lat) transformation. (I.e., find that lat-lon of the grid points.) Examples include: staggered grids, thinned Gaussian grids and irregular grids.

The -ll2i option takes a given latitude and longitude, finds the grid point that is closest to that specified latitude and longitude and prints out the index of the grid point. The -ll2i option uses the gctpc library and only supports a grids supported by gctpc. Note that updated -ll2i uses the Fortran convention which has the index starting at one. Note that the index is for the output grid which may be different from the input grid. For example, the GFS usually writes the grib files in WE:NS order. By default, wgrib2 will read a WE:NS input grid and convert it to to a WE:SN (output) grid. This is explained in the page for the -scan option.


-ll2i LON LAT
      LON is the longitude -180..360
      LAT is the latitude from -90..90
      option prints out the index,  0..number of grid points - 1


-sh-4.1$ wgrib2 png.grb2 -ll2i 11 22
1:4:11.000000 22.000000 -> (40332)
-sh-4.1$ wgrib2 png.grb2 -ilat 40332
1:4:grid pt 40331,lon=10.000000,lat=22.000000,val=3.3
See also: -ilat, -scan,

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Page last modified: March 3, 2016
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