A GrismMap is a specialised form of Mapping which transforms 1-dimensional coordinates using the
spectral dispersion equation described in FITS-WCS paper III
" Representation of spectral
coordinates in FITS
" . This describes the dispersion produced by gratings, prisms and
When initially created, the forward transformation of a GrismMap transforms input
" values into output wavelength values. The
" grism parameter
" is a dimensionless value
which is linearly related to position on the detector. It is defined in FITS-WCS paper III as
" the offset
on the detector from the point of intersection of the camera axis, measured in units of the effective
" . The units in which wavelength values are expected or returned is determined
by the values supplied for the GrismWaveR, GrismNRP and GrismG attribute: whatever
units are used for these attributes will also be used for the wavelength values.
A null Object pointer (AST__NULL) will be returned if this function is invoked with STATUS set to an error value, or if it should fail for any reason.