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CONS_DEC

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



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