source: trunk/ToBeReviewed/LECTURE/GRIB/read_grib_bds.pro @ 67

FUNCTION read_grib_bds, num, recstart, ni, nj
;
  offset = recstart+8
  a = assoc(num, bytarr(1, /nozero), offset-1)
  sizepds = bit2int([binary(a[1]), binary(a[2]), binary(a[3])])
  flag = binary(a[8])
  gdsnotomitted = flag[0]
  bmsnotomitted = flag[1]
  ddd =  bit2int([binary(a[27]), binary(a[28])], /checkneg)
;
  offset = offset+sizepds
;
  IF gdsnotomitted THEN BEGIN
    a = assoc(num, bytarr(1, /nozero), offset-1)
    sizedds = bit2int([binary(a[1]), binary(a[2]), binary(a[3])])
    offset = offset+sizedds
  ENDIF
;
  IF bmsnotomitted THEN BEGIN
    a = assoc(num, bytarr(1, /nozero), offset-1)
    sizebms = bit2int([binary(a[1]), binary(a[2]), binary(a[3])])
    offset = offset+sizebms
  ENDIF
;
  a = assoc(num, bytarr(1, /nozero), offset-1)
;
  sizebds = bit2int([binary(a[1]), binary(a[2]), binary(a[3])])
                                ; 
  flags = binary(a[4])
; BIT VALUE MEANING
; 1   0     Grid point data
;     1     Spherical Harmonic Coefficients
; 2   0     Simple packing 
;     1     Second order ("Complex") Packing 
; 3   0     Original data were floating point values
;     1     Original data were integer values
; 4   0     No additional flags at octet 14
;     1     Octet 14 contains flag bits 5 - 12
; 5         Reserved (set to 0)
; 6   0     Single datum at each grid point
;     1     Matrix of values at each grid point
; 7   0     No secondary bit maps
;     1     Secondary bit maps present
; 8   0     Second order values have constant width
;     1     Second order values have different widths
; 9-12      Reserved (set to 0)
;
  eee = bit2int([binary(a[5]), binary(a[6])], /checkneg)
;
  aaa = bit2int(binary(a[7]), /checkneg)
  bbb = bit2int([binary(a[8]), binary(a[9]), binary(a[10])])
  IF aaa LT 0 THEN rrr = -2.^(-24) * bbb * 16.^(-aaa-64) $
  ELSE rrr = 2.^(-24) * bbb * 16.^(aaa-64)
;
  nbits = (a[11])[0]
  CASE 1 OF
    flags[0] EQ 0 AND flags[1] EQ 0:BEGIN
      CASE nbits OF
        8 :a = assoc(num, bytarr(ni, nj, /nozero), offset-1+12)
        16:a = assoc(num, uintarr(ni, nj, /nozero), offset-1+12)
        32:a = assoc(num, ulonarr(ni, nj, /nozero), offset-1+12)
        64:a = assoc(num, ulon64arr(ni, nj, /nozero), offset-1+12)
        ELSE:
      ENDCASE
    END
  ENDCASE

  RETURN, (rrr+(a[0]*2.^(eee)))*10.^(-ddd)
END