Transform 1-dimensional coordinates using a grism dispersion equation


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 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.

Constructor Function



The GrismMap class inherits from the Mapping class.


In addition to those attributes common to all Mappings, every GrismMap also has the following attributes:


The GrismMap class does not define any new routines beyond those which are applicable to all Mappings.