FIXHEAD is used to reset or fix FITS headers with various pathologies.
ORIGIN and the related RORIGIN and CORIGIN cards are used to reset the FITS
coordinate system cards (CRVALn, CTYPEn, CRPIXn, CDELTn, and CNPIXn). This
is useful if the coordinate cards have been altered by programs (like IRAF
or STSDAS) in ways that cause problems with various VISTA image
manipulation programs, especially SHIFT. FIXHEAD ORIGIN can also be used
to strip out wavelength calibration information (but you cannot uncalibrate
a spectrum if it has been, for example, resampled onto a linear wavelength
scale). ORIGIN resets the coordinate info along both axes, CORIGIN and
RORIGIN only reset coordinates along the Columns and Rows axis,
respectively.
BLANK is used to remove any empty (blank) header cards. While blank cards
are allowed under the standard FITS definition for headers, they can be a
nuisance as they eat up available header memory.
GROUP removes various header cards related to the ``group'' structure
of complex FITS files. Since the current version of VISTA does not
recognize the group structure, these cards are eating up header memory.
WFPC is used to remove header cards in WF/PC1 imaging data. Again, the
purpose is to try to free up header memory, especially in old WF/PC1 image
which have huge image headers.