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