MARS/Dissemination

Specifies a Unix filename containing a bitmap definition. 

bitmap=<value>

specifies a UNIX filename containing a bitmap definition as described below. The specification is an ASCII text description of a rectangular area bitmap. The bitmap specification takes the form of a set of command-like definitions containing the following:

SPEC, a stand-alone command at the start of a bitmap specification.

SIZE=yy:xx, where yy indicates the number of rows, and xx indicates the number of points per row.

VALUES=OFF (default) or ON indicates whether subsequent changes to the bitmap are with respect to a bitmap preset to OFF (i.e. 0 bits) or to ON (i.e. 1 bits).

POINTS=jj:kk, where jj indicates the row number, and kk indicates which point(s) within the row take the opposite value to the value preset by VALUES. kk can take the general form of a list of values: k1/k2/k3/.../kn where the format of a value is:

    kk    depicting a single point
 k1-k2    indicating points from K1 to K2 inclusive
     0    no points

END, a stand-alone directive ending the specification.

The following example illustrates the use of the directives above. First the dissemination requirements:

DIS,COUNTRY=EC,TYPE=FC,LEVT=PL,LEVE=500,STEP=240,FORM=GRIB,PARA=GH,REPR=LL,GRID=0.5/0.5,AREA=4.5/0.0/0.0/4.5,
BITMAP=”ECM_001.BITMAP”

The bitmap specification is contained in a separate file, ECM_001.BITMAP, in the same directory as the file containing the dissemination requirements. It contains the following:

SPEC,SIZE=10:10,VALUES=OFF,
POINTS=01:03-08/10,
       03:02-04/07-09,
       04:02/03/08/09,
       06:0,
       07:01-03/08-10,
       09:01-10
END

and gives the following bitmap:

    0 0 1 1 1 1 1 1 0 1
    0 0 1 1 1 1 1 1 0 1
    0 1 1 1 0 0 1 1 1 0
    0 1 1 0 0 0 0 1 1 0
    0 1 1 0 0 0 0 1 1 0
    0 0 0 0 0 0 0 0 0 0
    1 1 1 0 0 0 0 1 1 1
    1 1 1 0 0 0 0 1 1 1
    1 1 1 1 1 1 1 1 1 1
    1 1 1 1 1 1 1 1 1 1

Notes:

1. Within POINTS, values for rows remain defined until new values are given. Thus, in the example above:
   
   • row 2 is the same as row 1
   • row 5 is the same as row 4
   • row 8 is the same as row 7
   • row 10 is the same as row 9
2. The definition of row 6 simply indicates that no points are to be switched from the preset value defined in VALUES.
3. If VALUES=ON had been coded, the values in the bitmap would all be reversed, thus:

    1 1 0 0 0 0 0 0 1 0 
    1 1 0 0 0 0 0 0 1 0 
    1 0 0 0 1 1 0 0 0 1 
    1 0 0 1 1 1 1 0 0 1 
    1 0 0 1 1 1 1 0 0 1 
    1 1 1 1 1 1 1 1 1 1 
    0 0 0 1 1 1 1 0 0 0 
    0 0 0 1 1 1 1 0 0 0 
    0 0 0 0 0 0 0 0 0 0 
    0 0 0 0 0 0 0 0 0 0

4. Member States may define a number of bitmaps in this way; it is suggested that, at least initially, this number be kept below about 20.
5. The same bitmap may be used for different areas, provided the areas conform with one another (i.e. have the same number of rows and columns).