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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 $*$ ( $*$ ) (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.


next up previous 264
Next: AST_GetTableHeader - Get the FITS headers from a FitsTable
Up: AST Routine Descriptions
Previous: AST_GRIDLINE - Draw a grid line (or axis) for a Plot

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council