- NAME
WCS_CHECK_CTYPE
- PURPOSE
Checks that a pair of CTYPE parameters conform to WCS format and return
the projection type and coordinate type extracted from them.
- EXPLANATION
Stops with an error message if CTYPE does not conform to standard,
unless one or both CTYPE strings is missing.
If only CTYPE[0] is present, and is valid, this counts as a
"pass".
If ctype is unset, returns silently, with coord_type = 'X' and
projection_type = 'DEF'.
Low-level procedure extracted from WCSXY2SPH & WCSSPH2XY to reduce code
duplication.
- CATEGORY
Mapping and Auxiliary FITS Routine
- CALLING SEQUENCE
wcs_check_ctype, ctype, projection_type, [coord_type]
- INPUT PARAMETERS
ctype - astrometry-related CTYPE strings extracted from the header.
- OUTPUT PARAMETERS
projection_type - three-character code specifying map projection.
If ctype is not specified returns 'DEF' for default.
coord_type - one- or two-character code specifying the coordinate
type, 'X' (unknown) if not specified. 'C' for RA & Dec.
- NOTES
The conventions followed here check consistency with
"Representations of Celestial Coordinates in FITS" by Calabretta
and Greisen (2002, A&A, 395, 1077; also see
http://fits.gsfc.nasa.gov/fits_wcs.html).
- PROCEDURE
Astrometry CTYPEs should come in longitude and latitude pairs in one
of three formats: 'RA---xxx' & 'DEC--xxx', 'yLON-xxx' & 'yLAT-xxx', or
'zzLN-xxx' & 'zzLT-xxx' where xxx is the projection code and y or zz
specify the type of the latitude & longitude axes, e.g. Galactic,
Ecliptic etc. If the CTYPE pair is in this format, xxx is returned as
the projection type.
- COMMON BLOCKS
none
- PROCEDURES CALLED
none
- AUTHOR
J. P. Leahy
- MODIFICATIONS/REVISION LEVEL
1.0 Jul 2013 Extracted from WCSXY2SPH & WCSSPH2XY
1.1 Aug 2013 Now does actually stop if error detected.
1.2 Jan 2014 Recognize when RA, DEC reversed, W. Landsman