CONS_DEC
Name
CONS_DEC
Purpose
Obtain the X and Y coordinates of a line of constant declination
Explanation
Returns a set of Y pixels values, given an image with astrometry, and
either
(1) A set of X pixel values, and a scalar declination value, or
(2) A set of declination values, and a scalar X value
Form (1) can be used to find the (X,Y) values of a line of constant
declination. Form (2) can be used to find the Y positions of a set
declinations, along a line of constant X.
Calling Sequence
Y = CONS_DEC( DEC, X, ASTR, [ ALPHA ])
Inputs
DEC - Declination value(s) in DEGREES (-!PI/2 < DEC < !PI/2).
If X is a vector, then DEC must be a scalar.
X - Specified X pixel value(s) for line of constant declination
If DEC is a vector, then X must be a scalar.
ASTR - Astrometry structure, as extracted from a FITS header by the
procedure EXTAST
Output
Y - Computed set of Y pixel values. The number of Y values is the
same as either DEC or X, whichever is greater.
Optional Output
ALPHA - the right ascensions (DEGREES) associated with the (X,Y) points
Restrictions
Implemented only for the TANgent, SIN and CAR projections
Notes
The algorithm (and notation) is based on AIPS Memo 27 by Eric Greisen,
with modifications for a coordinate description (CD) matrix as
described in Paper II of Greisen & Calabretta (2002, A&A, 395, 1077).
These documents are available from
http://www.cv.nrao.edu/fits/documents/wcs/wcs.html
Revision History
Written, Wayne Landsman STX Co. April 1988
Use new astrometry structure, W. Landsman HSTX Jan. 1994
Use CD matrix, add SIN projection W. Landsman HSTX April, 1996
Converted to IDL V5.0 W. Landsman September 1997
Fix case where DEC is scalar, X is vector W. Landsman RITSS Feb. 2000
Fix possible sign error introduced Jan. 2000 W. Landsman May 2000
Work for the CARee' projection W. Landsman May 2003