Transform 1-dimensional coordinates using a grism dispersion equation
"
Representation of spectral
coordinates in FITS"
. This describes the dispersion produced by gratings, prisms and
grisms.
When initially created, the forward transformation of a GrismMap transforms input "
grism
parameter"
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
local length"
. 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.
GrismNR: The refractive index at the reference wavelength
GrismNRP: Rate of change of refractive index with wavelength
GrismWaveR: The reference wavelength
GrismAlpha: The angle of incidence of the incoming light
GrismG: The grating ruling density
GrismM: The interference order
GrismEps: The angle between the normal and the dispersion plane
GrismTheta: Angle between normal to detector plane and reference ray