formats.doc

wgrib2 formats: -bin -ieee, -text 					Wesley Ebisuzaki 8/2013


The -bin, -ieee, -text output have two flavors depending on whether the
header flag is set (-header, default) or not set (-no_header)

Definitions

npts = number of points in the grid including undefined points (-npts)
nx, ny = for a "rectangular" grid, the dimensions of the grid.  For
         a non-rectangular grid, nx=npts and ny=1 (-nxny)


The -text, -bin and -ieee formats were adopted from wgrib. The differences
is that in scanning order went from raw to we:sn.


			-no_header -text Format


(grid 1)	(grid value)		grid value (text format)
		(grid value)
		...
		(grid value)		npts values
(grid 2)	(grid value)		grid value
		(grid value)
		...
		(grid value)		npts values
		...


			Binary and IEEE, no header

(grid 1)	(binary float value)		grid value (4 bytes with IEEE)
		(binary float value)
		...
		(binary float value)		npts values

(grid 2)	(binary float value)
		(binary float value)
		...
		(binary float value)		npts values
		etc

With binary, the binary float value is native floating point representation.
For the x86 cpus (intel, amd), this is little endian IEEE.  For IBM power
chips, this is big endian IEEE. For a Cray X-MP, the binary format will be
8 bytes long.  (No, I haven't compiled wgrib2 on a X-MP but this section
of the code came from wgrib which did run on the X-MP.)

With -IEEE, the grid point values are software converted to big endian IEEE
values.  (The code has no dependance the the native floating point format.)

Note: the default order of the grid points has a scanning order of WE:SN.
This may not be order that the grid points were stored in the grib message
(-order raw).  This is different from wgrib which is -order raw.


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 in 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 defaults to the binary/no-header format.

			-header -text Format


(grid 1)	(nx) (ny)		grid dimensions, two text integers
		(grid value)		grid value (text)
		(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, with header


(grid 1)	(binary integer)	npts*sizeof(float) (4 bytes with IEEE)
		(binary float value)	grid value (4 bytes with IEEE)
		...
		(binary float value)	npts values
		(binary integer)	npts*sizeof(float) (4 bytes)

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

The binary-with-header and IEEE-with-header is the f77 format binary file.
Each record starts with the size of the record in bytes stored as an integer.
With -ieee, the number is 4 bytes long stored as an unsigned integer in big
endian format. For -bin, the integer is stored in its native format. The
length of the integer is determined by the cpu (sizeof(int) bytes long).

The body of the message is the same as -ieee or -bin.