As of Fri Jul 19 8:22:51 2024

GETHEAD: Verb to read image header parameters into adverbs.


INNAME                             Image name(name).
INCLASS                            Image name(class).
INSEQ           0.0      9999.0    Image name(seq. #). 0=>high
INDISK          0.0         9.0    Disk drive #. 0=>any
KEYWORD                            Name of header parameter.
                                   See EXPLAIN GETHEAD for list.
         @     Output:adverbs
KEYVALUE @                         Value of a numeric parm. =
         @                         KEYVALUE(1) + KEYVALUE(2).
KEYSTRNG @                         Value of a character-valued
         @                         parameter.


Type: Verb
Use:  GETHEAD is used to read the contents of the parameters in the
      header into POPS adverbs.  It may be used on any kind of image
      or uv data set.
  INNAME......Image name(name).   Standard defaults.
  INCLASS.....Image name(class).  Standard defaults.
  INSEQ.......Image name(seq. #).  0 => highest.
  INDISK......Disk drive # of image.  0 => any
  KEYWORD.....The FITS name of the parameter.  No default.
              See EXPLAIN GETHEAD for list.  Minimum match is
Output adverbs:
  KEYVALUE....The value of a numeric parameter is returned as
              KEYVALUE(1) + KEYVALUE(2).  The second term will be
              non-zero only for double precision parameters and will
              be small.
  KEYSTRNG....The value of a character parameter.




     GETHEAD provides read access to essentially all parameters in the
AIPS standard header.  Its use for character-valued header parameters
is rather limited at the present time, because AIPS has only limited
character string manipulation operators.  However, for numeric
parameters, the possible uses of GETHEAD are very wide indeed.  For
example, to loop over all planes in a cube, a procedure could contain
the following statements:
             KEYWORD = 'NAXIS3'; GETHEAD
             FOR Z = 1 TO KEYVALUE(1);
             END ;
The list of keywords recognized by GETHEAD is given below:
'OBJECT  '     Source name (char*8)
'TELESCOP'     Telescope name (char*8)
'INSTRUME'     Receiver name (char*8)
'OBSERVER'     Observer name (char*8)
'DATE-OBS'     Date of observation (char*8 as yyyymmdd)
'DATE-MAP'     File creation date (char*8 as yyyymmdd)
'BUNIT   '     Brightness units (char*8)
'CTYPE1  ','CTYPE2  ','CTYPE3  ','CTYPE4  ','CTYPE5  ',
'CTYPE6  ','CTYPE7  '     Type of coordinate axis (char*8)
'CRVAL1  ','CRVAL2  ','CRVAL3  ','CRVAL4  ','CRVAL5  ',
'CRVAL6  ','CRVAL7  '     Value of coordinate at reference
                          pixel (real*8)
'CDELT1  ','CDELT2  ','CDELT3  ','CDELT4  ','CDELT5  ',
'CDELT6  ','CDELT7  '     Change of coordinate/pixel (real*4)
'CRPIX1  ','CRPIX2  ','CRPIX3  ','CRPIX4  ','CRPIX5  ',
'CRPIX6  ','CRPIX7  '     Reference pixel location (real*4)
'CROTA1  ','CROTA2  ','CROTA3  ','CROTA4  ','CROTA5  ',
'CROTA6  ','CROTA7  '     Rotation of coordinate (real*4)
'EPOCH   '     Epoch of coordinates (years, real*4)
'DATAMAX '     Maximum data value (real*4)
'DATAMIN '     Minimum data value (real*4)
'PRODUCT '     Clean product code: 1 - 4 => normal, components,
               residual, points  (integer)
'NITER   '     Number of Clean iterations (integer)
'BMAJ    '     Clean beam major axis (real*4, degrees)
'BMIN    '     Clean beam minor axis (real*4, degrees)
'BPA     '     Clean beam position angle (real*4, degrees)
'VELREF  '     Velocity definition code: 0 => none,
               1 - 3 => LSR, Sun, Obs  + 256 if radio
'ALTRVAL '     Alternate reference value: (real*8, frequency in Hz or
               velocity in m/sec)
'ALTRPIX '     Alternate reference pixel (real*4)
'OBSRA   '     Pointing position: RA (real*8, degrees)
'OBSDEC  '     Pointing position: Dec (real*8, degrees)
'RESTFREQ'     Line rest frequency (real*8, Hz)
'XSHIFT  '     Phase shift in RA (real*4, degrees)
'YSHIFT  '     Phase shift in Dec (real*4, degrees)
'PTYPE1  ','PTYPE2  ','PTYPE3  ','PTYPE4  ','PTYPE5  ','PTYPE6  ',
'PTYPE7  ','PTYPE8  ','PTYPE9  ','PTYPE10 ','PTYPE11 ','PTYPE12 ',
'PTYPE13 ','PTYPE14 '     Random parameter type (char*8)
'SORTORD '     Sort order (char*2, UV data only)
'BLANK   '     Value of blanked pixel (real*4, floating maps only)
'IMNAME  '     Image name (char*12)
'IMCLASS '     Image class (char*6)
'IMSEQ   '     Image sequence number (integer)
'GCOUNT  '     Number of "groups" (real*8, UV data only)
                  this is the number of visibilities.
'PCOUNT  '     Number of random parameters (integer, UV data only)
'NAXIS   '     Number of axes (integer)
'NAXIS1  ','NAXIS2  ','NAXIS3  ','NAXIS4  ','NAXIS5  ',
'NAXIS6  ','NAXIS7  '     Number of points on axis n (integer)
'USERNO  '     Image owner number (integer)
'IMTYPE  '     Image type (character*2, MA or UV)
'EXTYPE11', through 'EXTYPE50'
               Extension file type n (character*2)
'EXTVER11', through 'EXTVER50'
               Max extension file version number (integer)
'IMGTYPE'      Image type: 1 non 3D, 2 3-D imaging
'XPOFF'        X offset of original image center from reference pixel
'YPOFF'        Y offset of original image center from reference pixel

Units: The units throughout are those of FITS (m-k-s plus degrees and
Jy).  In other words, angle coordinate reference values and increments
are in degrees, frequencies are in Hz, velocities in m/s.

AIPS headers now can also contain extra parameters represented within
the header file as keyword/value pairs.  If GETHEAD does not recognize
a keyword as part of its basic list, it will attempt to read it as a
header keyword and report any failure as a keyword missing error.  Two
keywords which are placed in this category by RESCALE are:

'ISCALE  '     Map scale factor (real*8)
'IZERO   '     Map offset       (real*8)
                  Current = ISCALE * initial  + IZERO

The verb IMHEADER will show all current header keywords of this sort.