While applications should be written in an instrument independent fashion, it is still useful to obtain information about the properties of a particular psf, often resulting in substantial efficiency improvements. If a psf initialiser has specified a hint routine then the psf system will call it in attempt to get the value of a named hint. Standard hint names are defined in PSF_PAR. Not all hints need be supported -- the psf system returns both a "hint available" flag and the hint data to the client.
The hint routine signature is,
SUBROUTINE psf_hint_rtn( INTEGER psid, CHAR hintname, BYTE data[],
INTEGER status )
Each hint has a natural data type. Most are logical but a few are single
precision real numbers. Where the real number refers to a spatial scale
the units are radians. A type hint might be whether or not the psf exhibits
a particular symmetry on the detector, such as azimuthal symmetry.