wgrib v1.2					Wesley Ebisuzaki
        Portable Grib decoder for NMC Reanalysis

   The program wgrib reads GRIB data and writes out data in the 
following different formats: text, GRIB, IEEE and binary (native cpu format).
The easiest of the formats to read is text followed by binary, IEEE and
finally GRIB.  All except the GRIB format allows two flavors,
with and without headers.  You may be wondering why wgrib supports
IEEE and GRIB.  The IEEE was added so that the CRAY could produce
`easy to read' binary files, and the GRIB option was added so that
wgrib could extract and reorder records in a grib file.




				Text Format


(grid 1)	(nx) (ny)		grid dimensions
		(grid value)
		(grid value)
		...
		(grid value)		nx*ny values
(grid 2)	(nx) (ny)		grid dimensions
		(grid value)
		(grid value)
		...
		(grid value)		nx*ny values
		...


			Binary and IEEE, no header

(grid 1)	(binary float value)		grid value
		(binary float value)
		...
		(binary float value)		nx*ny values

(grid 2)	(binary float value)
		(binary float value)
		...
		(binary float value)		nx*ny values
		etc

	The no-header format is not a recommended format to use.  
The format does not indicate the size of the grid. If your program 
makes a mistake on the grid dimension, you could get interesting results.  
However, some fortran compilers require this format for binary files (Cray, 
ABSoft under AmigaOS).  In addition, GrADs likes the binary/no-header
format.



			Binary and IEEE, with header


(grid 1)	(binary integer)	nx*ny*sizeof(float)
		(binary float value)
		...
		(binary float value)	nx*ny values
		(binary integer)	nx*ny*sizeof(float)

(grid 2)	(binary integer)	nx*ny*sizeof(float)
		(binary float value)
		...
		(binary float value)	nx*ny values
		(binary integer)	nx*ny*sizeof(float)


    The binary-with-header format is commonly used by UNIX 
fortrans for their binary files.  Some MS-DOS fortran compilers
also support this format.  The CRAY fortran supports the IEEE
format by the "assign -Ff77 -Nieee u:iunit" command.


                            Spectral Data

The format for spectral data is similar to the gridded data except
nx = 2 * number of complex coefficients, and ny = 1.  As you would
expect, the real part is followed by the imaginary part.  For more 
details, consult the GRIB format specifications.

			Organization of the Grid

    Standard NMC practice is to store the grids in fortran order
starting from the north and working southward, and on the 0E and
working eastward.  No effort has been made in wgrib to implement
the scan order option in GRIB.  For lat-long grids, the dimensions
are 144 x 73.  The first point is 90N 0E, the second point is 
90N 2.5E, and you can figure out the rest.  For Gaussian grids, the
dimensions are 192 x 94.  The first grid point is at 88.542N 0E,
the second grid point is at 88.542N 1.875E.  In theory, the Gaussian
latitudes (for a Gaussian grid) are determined by the zeros of
a long polynomial.  In practice, the Gaussian latitudes are almost
equally spaced.  For plotting purposes, I assume that the Gaussian
latitudes have a spacing of (88.542 - -88.542)/(94 - 1) degrees of 
latitude.

    The above description of the grid format only applies to this
version of Reanalysis.  Future Reanalysis products may have different
resolutions.  If you use wgrib for non-Reanalysis products, then
you are on your own.  GRIB allows you to define specialized grids
in different scanning orders.  wgrib may or may not correctly
decode these GRIB files and definitely will not try to make sense
of the scanning order.


Note: undefined values are set to 9.999e20.
(see UNDEFINED in bds.h and/or all.c)