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HEULER

HEULER

Name


      HEULER

Purpose


      Change the coordinate system of a FITS header or astrometry structure

Explanation


      Converts a FITS header or a astrometry structure containing WCS (world
      coordinate system) information between celestial, ecliptic, and
      Galactic coordinates

Calling Sequence


      HEULER, hdr, [/GALACTIC, /CELESTIAL, /ECLIPTIC, ALT_IN = , ALT_OUT=]
                      or
      HEULER, astr, /GALACTIC, /CELESTIAL, /ECLIPTIC

Input/output Parameters


      hdr - FITS header (string array) containing WCS information
                            or
      Astr - Astrometry structure as extracted from a FITS header
            by extast.pro (See EXTAST for more info).
      Header or astrometry structure will be modified by the program to
      contain astrometry in the new coordinates system.
  REQUIRED INPUT KEYWORDS:
      One of the following exclusive keywords is *required*
      /GALACTIC - Convert the header to Galactic coordinates
      /CELESTIAL - Convert the header to celestial (RA & Dec) coordinates
      /ECLIPTIC - Convert the header to ecliptic coordinates

Optional Input Keywords


      The following two keywords apply if the FITS header contains multiple
      WCS keywords. See Section 3.3 of Greisen & Calabretta (2002, A&A, 395,
      1061) for information about alternate astrometry keywords.
      ALT_IN - single character 'A' through 'Z' or ' ' specifying an
          alternate astrometry system present in the input FITS header. The
          default isto use the primary astrometry or ALT = ' '. If /ALT_IN
          is set, then this is equivalent to ALT_IN = 'A'.
      ALT_OUT - single character specifying the alternate WCS keywords
          to write the *output* astrometry. If not specified, then ALT_OUT
          is set equal to ALT_IN.

Restrictions


      Currently assumes that celestial and ecliptic coordinates are in
      J2000. Use HPRECESS if this is not the case.
      ST Guide Star (DSS) image headers are first converted to a standard
      tangent projection, prior to the coordinate conversion

Method


      The algorithm used is described in Section 2.7 of Calabretta & Greisen
      (2002, A&A, 395, 1077). The CRVAL coordinates are transformed
      directly using EULER. The new LONPOLE and LATPOLE values are then
      determined by transforming the pole of the new system to the old, and
      converted to native coordinates using WCS_ROTATE.

Example


      A FITS header, hdr, has a standard tangent projection WCS information.
      Add an alternate 'G' Galactic projection. Note that the original
      WCS information will be left unchanged
      IDL> heuler, hdr, /Galactic, alt='G'

Procedures Used


      EULER, EXTAST, GSSS_STDAST, PUTAST, SXADDHIST, WCS_ROTATE

Revision History


      Written W. Landsman June 2003
      Use PV2 tag in astrometry structure rather than PROJP1 W. L. May 2004
      Use double precision to compute new North pole W.L. Aug 2005
      Check for non-standard CTYPE value W.L. Sep 2012



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