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      Cursor controlled display of image intensities and astronomical coords


      CURVAL displays different information depending whether the user
      supplied an image array, and/or a FITS header array
      Note that in the usual truecolor mode, the byte intensity returned by
      CURVAL does not correspond to the byte scaled image value but rather
      returns the maximum value in each color gun.
      curval ;Display x,y and byte intensity (inten)
      curval, im ;Display x,y,inten, and also pixel value (from image array)
      curval, hdr, [ im, OFFSET= , ZOOM=, FILENAME=, ALT=]

Optional Inputs

      Hdr = FITS Header array
      Im = Array containing values that are displayed. Any type.

Optional Keyword Inputs

      ALT - single character 'A' through 'Z' or ' ' specifying an alternate
            astrometry system present in the FITS header. The default is
            to use the 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.
      OFFSET - 2 element vector giving the location of the image pixel (0,0)
              on the window display. OFFSET can be positive (e.g if the
              image is centered in a larger window) or negative (e.g. if the
              only the central region of an image much larger than the window
              is being displayed.
              Default value is [0,0], or no offset.
      ZOOM - Scalar specifying the magnification of the window with respect
              to the image variable. Use, for example, if image has been
              REBINed before display.
      FILENAME = name of file to where CURVAL data can be saved.
              Data will only be saved if left or center mouse button
              are pressed.



Side Effects

      X and Y values, etc., of the pixel under the cursor are constantly
      Pressing left or center mouse button prints a line of output, and
      starts a new line.
      Pressing right mouse button exits the procedure.
      If the keyword FILENAME is defined, the date and time, and a heading
      will be printed in the file before the data.

Procedures Called


Revision History

      Written, K. Rhode, STX May 1990
      Added keyword FILENAME D. Alexander June 1991
      Don't write to Journal file W. Landsman March 1993
      Use astrometry structure W. Landsman Feb 1994
      Modified for Mac IDL I. Freedman April 1994
      Allow for zoomed or offset image W. Landsman Mar 1996
      Proper rounding of zoomed pixel values W. Landsman/R. Hurt Dec. 1997
      Remove unneeded calls to obsolete !ERR W. Landsman December 2000
      Replace remaining !ERR calls with !MOUSE.BUTTON W. Landsman Jan 2001
      Allow for non-celestial (e.g. Galactic) coordinates W. Landsman Apr 2003
      Work if RA/Dec reversed in CTYPE keyword W. Landsman Feb. 2004
      Always call UNZOOM_XY for MOUSSE compatibility W. Landsman Sep. 2004
      Added ALT keyword W. Landsman October 2004
      Always test if offset/zoom supplied W. Landsman Feb 2008

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