v1.6 update 5/98 update 9/03

                              -H Option
                              -- ------

Some people have fortran/C programs which read the binary/IEEE
output from wgrib.  They found that they needed a header to
identify each record.  I can see the need to identify each
record but my choice would to have the fortran/C program
open two files, the data file and the corresponding inventory.
However, people have different styles.

The -H option adds a "universal" header to the binary/IEEE
file. The header is "universal" because it contains all the
meta-data (PDS and GDS).  Nobody can complain that I left out 
some crucial information from the header.

The PDS (Product Definition Section) and GDS (Grid Definition
Section) are documented in the GRIB references such as Office
Note 388 by John Stackpole (available from the NCEP ftp site).


                            Output Format

Case 1: (GRIB file has GDS)

        integer:		length of PDS + 4
        character*4:		"PDS "
	PDS			sequence of bytes
	integer:		length of PDS + 4

	integer:		length of GDS + 4
	character*4:		"GDS "
	GDS			sequence of bytes
	integer:		length of GDS + 4

        (decoded GRIB message/record)

Case 2: (missing GDS)

        integer:		length of PDS + 4
        character*4:		"PDS "
	PDS			sequence of bytes
	integer:		length of PDS + 4

	integer:		length of 4
	character*4:		"GDS "
	integer:		length of 4

        (decoded GRIB message/record)

When the output file is IEEE, the "integer" is big-endian
four byte integer.  Otherwise it is the native format 
integer.  

As you can see, the "universal" header is really two f77-style
headers.  The first header contains the string "PDS " along with
the PDS.  The second header contains the string "GDS " along with
the GDS (if present).

The main complication in reading this header is that it is
variable length.  C programs will have no problems.  Reading
the file in fortran as an unformatted sequential file will
require a trick.

c
c       sample of reading the PDS in a file created using
c       -H (include PDS & GDS) and -h (f77 style headers, default)
c
c       example: wgrib -d 1 -H grib_file -o dump
c

        character*1 pds(100),c4(4),gds(1000)
        open(unit=1,file='dump',form='unformatted')
c
c  Read "PDS " and Length of the PDS
        read(1) c4, (pds(i),i=1,3)
c
c  Check for letters "PDS " in  PDS
        if (c4(1).ne.'P') goto 9999
        if (c4(2).ne.'D') goto 9999
        if (c4(3).ne.'S') goto 9999
        if (c4(4).ne.' ') goto 9999
c  Calculate length of variable PDS
        lenpds=ichar(pds(1))*256*256+ichar(pds(2))*256+ichar(pds(3))
c
c  Print out length
        write(*,*) 'Length of variable PDS in the header=', lenpds
c
c  Backspace
        backspace(1)
c
c  Read PDS using the length information
        read(1) c4, (pds(i),i=1,lenpds)
c
c  Convert a character argument to an integer based on the character position
c in the collating sequence
        idog1=ichar(pds(13))
        idog2=ichar(pds(14))
        idog3=ichar(pds(15))
c
        write(6,20)idog1,idog2,idog3
20      format('PDS :',i10,1x,i5,1x,i6)
c
c --------------------------------------------------------------------------
c  Read "GDS " and Length of the GDS
        read(1) c4, (gds(i),i=1,3)
c
c  Check for letters "GDS " in  the GDS
        if (c4(1).ne.'G') goto 9999
        if (c4(2).ne.'D') goto 9999
        if (c4(3).ne.'S') goto 9999
        if (c4(4).ne.' ') goto 9999
c
c  Calculate length of variable GDS
        lengds=ichar(gds(1))*256*256+ichar(gds(2))*256+ichar(gds(3))
c
c  Print out length
        write(*,*) 'Length of variable GDS in the header=', lengds
c
c  Backspace
        backspace(1)
c
c  Read GDS using the length information
        read(1) c4, (gds(i),i=1,lengds)
c
c  Convert a character argument to an integer based on the character position
c in the collating sequence
        idog1=ichar(gds(13))
        idog2=ichar(gds(14))
        idog3=ichar(gds(15))
c
        write(6,22)idog1,idog2,idog3
22      format('GDS: ',i10,1x,i5,1x,i6)
c
        STOP
c
c  Error Warning
9999    write(*,*) 'Error in beginning of PDS or GDS'

        STOP
        END








                              -dwdgrib OPTION
                              -------- ------

The code for this option was submitted by Hulmut P. Frank (8/03) and completely
rewritten by WNE for inclusion to wgrib v1.8.0.4.  DWD (Deutscher Wetterdienst,
the german weather service) has a particular formatting of grib files:

    0                     (4 bytes)
    rec_len #1            (4 byte integer, big endian, length of grib msg #1 in bytes)
    grib msg #1
    rec_len #1            (4 byte integer, big endian, length of grib msg #1 in bytes)
    rec_len #2            (4 byte integer, big endian, length of grib msg #2 in bytes)
    grib msg #2
    rec_len #2            (4 byte integer, big endian, length of grib msg #2 in bytes)
    ...
    rec_len #N            (4 byte integer, big endian, length of grib msg #N in bytes)
    grib msg #N
    rec_len #N            (4 byte integer, big endian, length of grib msg #N in bytes)
    0                     (4 bytes)
 
This format looks like a f77 format of grib with a leading/trailing zeros.  Of
course, this format is perfectly legal grib and older wgribs could read the dwd files.
With v1.8.04, wgrib can write dwd format grib files.