       CATALOGUE BLOCK FORMAT

        February 10, 1981 modification

Listing below gives pointer values and byte lengths and offsets
appropriate to standard 16-bit machines.  Order of data will be
that listed below on all machines even though the detailed lengths
and pointers may be different.


OFFSET LENGTH TYPE  POINTER      DESCRIPTION

    0     8   C*8    K4OBJ=  1   Source name
    8     8   C*8    K4TEL=  3   Telescope, i.e. 'VLA'
   16     8   C*8    K4INS=  5   e.g. receiver or correlator
   24     8   C*8    K4OBS=  7   Observer name
   32     8   C*8    K4DOB=  9   Observation date in format 'DD/MM/YY'
   40     8   C*8    K4DMP= 11   Date map created in format 'DD/MM/YY'
   48     8   C*8    K4BUN= 13   Map units, i.e. 'JY/BEAM '
   56    7*8  C*8(7) K4PTP= 15   Random Parameter types
                  ( K2PTPN= 7 )
  112    7*8  C*8(7) K4CTP= 29   Coordinate type, i.e. 'LL'
                  ( K2CTPN= 7 )
  168     8   R*8    K8BSC= 22   Map scaling factor
  176     8   R*8    K8BZE= 23   Map offset factor: Real value =
                                 BSCALE * pixel + BZERO
  184    56   R*8(7) K8CRV= 24   Coordinate value at reference pixel
                  ( K2CTPN= 7 )
  240    28   R*4(7) K4CIC= 61   Coordinate value increment along axis
                  ( K2CTPN= 7 )
  268    28   R*4(7) K4CRP= 68   Coordinate Reference Pixel
                  ( K2CTPN= 7 )
  296    28   R*4(7) K4CRT= 75   Coordinate Rotation Angles
                  ( K2CTPN= 7 )
  324     4   R*4    K4EPO= 82   Epoch of coordinates (years)
  328     4   R*4    K4DMX= 83   Real value of data maximum
  332     4   R*4    K4DMN= 84   Real value of data minumum
  336     4   R*4    K4BLK= 85   Value of indeterminate pixel (real
                                 maps only)
  340     4   I*2(2) K2GCN=171   Number of random par. groups given as
                                 a Pseudo-I*4 number
  344     2   I*2    K2PCN=173   Number of random parameters
  346     2   I*2    K2DIM=174   Number of coordinate axes
  348    14   I*2(7) K2NAX=175   Number of pixels on each axis
                  ( K2CTPN= 7 )
  362     2   I*2    K2BPX=182   Code for pixel type: 1 integer,
                                 2 real, 3 dbl prec, 4 complex, 5 dbl
                                 prec complex
  364     2   I*2    K2INH=183   For integer maps: < 0 the value of an
                                 indeterminate pixel, > 0 the number
                                 of bits used to represent noise est.
                                 = 0 no blanking of pixels
  366     2   I*2    K2IMS=184   Image sequence no.
  368    12   C*12   K4IMN= 93   Image name
                  ( K4IMNO= 1 )  Character offset in packed string
  380     6   C*6    K4IMC= 93   Image class
                  ( K4IMCO=13 )  Character offset in packed string
  386     2   C*2    K4PTY= 93   Map physical type (i.e. 'MA','UV')
                  ( K4PTYO=19 )  Character offset in packed string
  388     2   I*2    K2IMU=195   Image user ID number
  390    40   I*2(20) K2EXT=196  Names of subsidiary file types
                  ( K2EXTN=20 )  (i.e. 'PL') 2 char unpacked form
  430    40   I*2(20) K2VER=216  Number of versions of corresponding
                  ( K2EXTN=20 )  subsidiary file
  470     2   I*2    K2NIT=236   # clean iterations
  472     2   I*2    K2BMJ=237   Beam major axis in .01 x-pixel units
  474     2   I*2    K2BMN=238   Beam minor axis in .01 x-pixel units
  476     2   I*2    K2BPA=239   Beam position angle in .01 deg units
  478     2   I*2    K2TYP=240   Clean map type: 1-4 => normal,
                                 components, residual, points
                    COMMENTS

General

1.  Standard names are given for the pointer variables.  The values
    for the pointers are computed by the subroutine VHDRIN and are
    machine-dependent.  The values given above are for standard 16-
    bit machines.  The values are found in the common /HDRVAL/ via
    includes 'DHDR.INC' and 'CHDR.INC'.  The characters of each C*8
    variable are packed separately (and left-justified) in as many
    real variables as required.  The image name, class, and physical
    type are packed as a 20-character string in as many real variables
    as required.
2. The header contains 256 words and should be contained in the arrays
   (e.g.) HEAD2(256),HEAD4(128) and HEAD8(64) which are equivalenced
   Pointers of the type K2... should refer to HEAD2 locations, K4...
   to HEAD4 locations, and K8... to HEAD8 locations.
   E.g.  HEAD8(K8BSC) contains the R*8 map scaling factor.

Specific

Byte 16:   Any special equipment etc. used during observations
Byte 56:   Random parameters are those associated with an irregularly
           gridded "array".  See latest FITS (u-v) paper for details.
Byte 112:  Seven coordinates!!!  Four will commonly be used; RA,
           DEC, FREQ and STOKES.
Byte 184:  In keeping with the FITS format convention, angles are
           expressed in degrees.
Byte 324:  Somewhat astronomically specific.  1950.0 is used.
Byte 328:  The real value of the max/min, not the pixel value
     332   is used.
Byte 336:  The value used to specify that a pixel is undefined.  Used
           only for floating point maps.
Byte 340:  Cannot use an I*4 format in some machines, hence this
           double I*2 format.
Byte 344:  See Byte 56:
Byte 364:  Confused at the moment.  If negative, then this is the value
           used as the pixel value for indeterminate pixels.  If > 0,
           then this is the number of bits used to represent the
           quality of a pixel value.  In this case, the true pixel
           value = (stored / 2 ** #bits) * BSCALE  +  BZERO.  The
           noise at each pixel is represented by the lsb's, with zero
           meaning the least reliable.
           bits in a map pixel to represent the inherent signal
           to noise of the data point.
Byte 366:  The user mapname-sequence number
Byte 368:  The user mapname-name
Byte 380:  The user mapname-class
Byte 390:  The types of subsidiary files associated with the
           map are given by a two letter designation; eg.'HI'
           for history files, 'PL' plot file.
Byte 430:  The current highest version number of the associated file
           type listed in the same relative array position in the
           previous type listing.
Byte 480:  Beginning of 16 spare words.
