Introduction

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

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 -ll2ij option takes a given latitude and longitude, finds the grid point that is closest to that specified latitude and longitude and prints out the ix and iy of the grid point. The -ll2i option uses the gctpc library and only supports a grids supported by gctpc.

See also: -ijlat, -ll2i