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    Put WCS astrometry parameters into a given FITS header.

Calling Sequence

    putast, hdr ;Prompt for all values
    putast, hdr, astr, [EQUINOX =, CD_TYPE =, ALT= , NAXIS=]
    putast, hdr, cd,[ crpix, crval, ctype], [ EQUINOX =, CD_TYPE =, ALT= ]


    HDR - FITS header, string array. HDR will be updated to contain
            the supplied astrometry.
    ASTR - IDL structure containing values of the astrometry parameters
            See EXTAST.PRO for more info about the structure definition
    CD - 2 x 2 array containing the astrometry parameters CD1_1 CD1_2
                                                            CD2_1 CD2_2
              in units of DEGREES/PIXEL
    CRPIX - 2 element vector giving X and Y coord of reference pixel
              (e.g. first pixel in image is [1,1] ) AND NOT IDL STANDARD
              (first pixel in image is [0,0]
    CRVAL - 2 element vector giving R.A. and DEC of reference pixel
              in degrees
    CTYPE - 2 element string vector giving projection types for the two axes.
            For example, to specify a tangent projection one should set
            ctype = ['RA---TAN','DEC--TAN']
    Fields added for version 2:
      .PV1 - Vector of projection parameters associated with longitude axis
      .AXES - 2 element integer vector giving the FITS-convention axis
              numbers associated with astrometry, in ascending order.
              Default [1,2].
      .REVERSE - byte, true if first astrometry axis is Dec/latitude
      .COORDSYS - 1 or 2 character code giving coordinate system, including
                'C' = RA/Dec, 'G' = Galactic, 'E' = Ecliptic, 'X' = unknown.
      .RADECSYS - String giving RA/Dec system e.g. 'FK4', 'ICRS' etc.
      .EQUINOX - Double giving the epoch of the mean equator and equinox
      .DATEOBS - Text string giving (start) date/time of observations
      .MJDOBS - Modified julian date of start of observations.
      .X0Y0 - Not written to header.


      HDR - FITS header now contains the updated astrometry parameters
              A brief HISTORY record is also added.

Optional Keyword Inputs

      ALT - single character 'A' through 'Z' or ' ' specifying an alternate
              astrometry system to write in the FITS header. The default is
              to write primary astrometry or ALT = ' '. If /ALT is set,
              then this is equivalent to ALT = 'A'. See Section 3.3 of
              Greisen & Calabretta (2002, A&A, 395, 1061) for information about
              alternate astrometry keywords.
      CD_TYPE - Integer scalar, either 0, 1 or 2 specifying how the CD matrix
                is to be written into the header
              (0) write PCn_m values along with CDELT values
              (1) convert to rotation and write as a CROTA2 value (+ CDELT)
              (2) as CDn_m values (IRAF standard)
            All three forms are valid representations according to Greisen &
            Calabretta (2002, A&A, 395, 1061), also available at
            http://fits.gsfc.nasa.gov/fits_wcs.html ) although form (0) is
            preferred. Form (1) is the former AIPS standard and is now
            deprecated and cannot be used if any skew is present.
            If CD_TYPE is not supplied, PUTAST will try to determine the
            type of astrometry already in the header. If there is no
            astrometry in the header then the default is CD_TYPE = 2.
      EQUINOX - numeric scalar giving the year of equinox of the reference
                coordinates. Keyword value takes precedence over value in
                astrometry structure which takes precedence over value in
                header; if none of these present then default is 2000.
      NAXIS - By default, PUTAST does not update the NAXIS keywords in the
            FITS header. If NAXIS is set, and an astrometry structure is
            supplied then the NAXIS1 and NAXIS2 keywords in the FITS header
            will be updated with the .NAXIS structure tags values. If an
            astrometry structure is not supplied, then one can set NAXIS to a
            two element vector to update the NAXIS1, NAXIS2 keywords.


      The recommended use of this procedure is to supply an astrometry
      structure. This can be produced with MAKE_ASTR.
      If parameters are supplied by keyword, the full range of
      astrometry header info is not supported by PUTAST.
      PUTAST does not delete astrometry parameters already present in the
      header, unless they are explicity overwritten.
      If present in the astrometry structure, PUTAST will add SIP
      ( http://fits.gsfc.nasa.gov/registry/sip.html ) or TPV
      ( http://fits.gsfc.nasa.gov/registry/tpvwcs.html ) distortion parameters
      to a FITS header.


      If only a header is supplied, the user will be prompted for a plate
      scale, the X and Y coordinates of a reference pixel, the RA and
      DEC of the reference pixel, the equinox of the RA and Dec and a
      rotation angle.

Procedures Used


Revision History

      Written by W. Landsman 9-3-87
      Major rewrite, use new astrometry structure March, 1994
      Use both CD and CDELT to get plate scale for CD_TYPE=1 September 1995
      Use lower case for FITS keyword Comments W.L. March 1997
      Fixed for CD_TYPE=1 and CDELT = [1.0,1.0] W.L September 1997
      Default value of CD_TYPE is now 2, Use GET_COORDS to read coordinates
      to correct -0 problem W.L. September 1997
      Update CROTA1 if it already exists W.L. October 1997
      Convert rotation to degrees for CD_TYPE = 1 W. L. June 1998
      Accept CD_TYPE = 0 keyword input W.L October 1998
      Remove reference to obsolete !ERR W.L. February 2000
      No longer support CD001001 format, write default tangent CTYPE value
      consistent conversion between CROTA and CD matrix W.L. October 2000
      Use GET_EQUINOX to get equinox value W.L. January 2001
      Update CTYPE keyword if previous value is 'LINEAR' W.L. July 2001
      Use SIZE(/TNAME) instead of DATATYPE() W.L. November 2001
      Allow direct specification of CTYPE W.L. June 2002
      Don't assume celestial coordinates W. Landsman April 2003
      Make default CD_TYPE = 2 W. Landsman September 2003
      Add projection parameters, e.g. PV2_1, PV2_2 if present in the
      input structure W. Landsman May 2004
      Correct interactive computation of image center W. Landsman Feb. 2005
      Don't use CROTA (CD_TYPE=1) if a skew exists W. Landsman May 2005
      Added NAXIS keyword W. Landsman January 2007
      Update PC matrix, if CD_TYPE=0 and CD matrix supplied W.L. July 2007
      Don't write PV2 keywords for WCS types that don't use it W.L. Aug 2011
      Add SIP distortion parameters if present W.L. April 2012
      Work if empty distortion structure present W.L. November 2012
      Spurious error message introduced April 2012 if CD matrix rather
        than structure supplied W.L. January 2013
      Allow for version 2 astrometry structure J. P. Leahy July 2013
      Bug fix in interactive use JPL Aug 2013.
      Support IRAF TNX projection M. Sullivan U. of Southamptom March 2014
      PV1_3, PV1_4 keywords take precedence over LONPOLE, LATPOLE keywords
                  WL, August 2014

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