### AST_GRISMMAP

Create a GrismMap

#### Description:

This function creates a new GrismMap and optionally initialises its attributes.

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.

#### Invocation

RESULT = AST_GRISMMAP( OPTIONS, STATUS )

#### Arguments

##### OPTIONS = CHARACTER $\ast$ ( $\ast$ ) (Given)
A character string containing an optional comma-separated list of attribute assignments to be used for initialising the new GrismMap. The syntax used is identical to that for the AST_SET routine.
##### STATUS = INTEGER (Given and Returned)
The global status.

#### Returned Value

##### AST_GRISMMAP = INTEGER
A pointer to the new GrismMap.

#### Notes:

• 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.