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      Make a contour plot labeled with astronomical coordinates.


      The type of coordinate display is controlled by the keyword TYPE
      Set TYPE=0 (default) to measure distances from the center of the image
      (IMCONTOUR will decide whether the plotting units will be in
      arc seconds, arc minutes, or degrees depending on image size.)
      Set /TYPE for standard RA and Dec labeling
      By using the /NODATA keyword, IMCONTOUR can also be used to simply
      provide astronomical labeling of a previously displayed image.

Calling Sequence

                            XMID=, YMID= ]


      IM - 2-dimensional image array
      HDR - FITS header associated with IM, string array, must include
              astrometry keywords. IMCONTOUR will also look for the
              OBJECT and IMAGE keywords, and print these if found and the
              PUTINFO keyword is set.
      /TYPE - the type of astronomical labeling to be displayed. Either set
              TYPE = 0 (default), distance to center of the image is
              marked in units of Arc seconds, arc minutes, or degrees
              TYPE = 1 astronomical labeling with Right ascension and
      /PUTINFO - If set, then IMCONTOUR will add information about the image
              to the right of the contour plot. Information includes image
              name, object, image center, image center, contour levels, and
              date plot was made
      XDELTA, YDELTA - Integer scalars giving spacing of labels for TYPE=1.
              Default is to label every major tick (XDELTA=1) but if
              crowding occurs, then the user might wish to label every other
              tick (XDELTA=2) or every third tick (XDELTA=3)
      XMID, YMID - Scalars giving the X,Y position from which offset distances
              will be measured when TYPE=0. By default, offset distances
              are measured from the center of the image.
      /OVERLAY - If set, then IMCONTOUR is assumed to overlay an image.
              This requires 1 extra pixel be included on the X and Y axis,
              to account for edge effects in the image display. Setting
              OVERLAY provide a better match of the contour and underlying
              image but is not as aesthetically pleasing because the contours
              will not extend to the axes.
      Any keyword accepted by CONTOUR may also be passed through IMCONTOUR
      since IMCONTOUR uses the _EXTRA facility. IMCONTOUR uses its own
      defaults for the XTITLE, YTITLE XMINOR, YMINOR, and SUBTITLE keywords
      but these may be overridden. Note in particular the /NODATA keyword
      which can be used if imcontour.pro is to only provide labeling.


      (1) The contour plot will have the same dimensional ratio as the input
          image array
      (2) To contour a subimage, use HEXTRACT before calling IMCONTOUR
      (3) Use the /NODATA keyword to simply provide astronomical labeling
          of a previously displayed image.
      (4) The IMCONTOUR display currently does not indicate the image
          rotation in any way, but only specifies coordinates along the
          edges of the image


      Overlay the contour of an image, im2, with FITS header, h2, on top
      of the display of a different image, im1. Use RA, Dec labeling, and
      seven equally spaced contour levels. The use of a program like
      David Fanning's cgImage http://www.idlcoyote.com/programs/cgimage.pro
      is suggested to properly overlay plotting and image coordinates. The
      /Keep_aspect_ratio keyword must be used.
      IDL> cgimage,im1,/keep_aspect, position = pos
      IDL> imcontour,im2,h2,nlevels=7,/Noerase,/TYPE,position = pos

Procedures Used


Revision History

      Written W. Landsman STX May, 1989
      Fixed RA,Dec labeling W. Landsman November, 1991
      Fix plotting keywords W.Landsman July, 1992
      Recognize GSSS headers W. Landsman July, 1994
      Removed Channel keyword for V4.0 compatibility June, 1995
      Add _EXTRA CONTOUR plotting keywords W. Landsman August, 1995
      Add XDELTA, YDELTA keywords W. Landsman November, 1995
      Use SYSTIME() instead of !STIME August, 1997
      Remove obsolete !ERR system variable W. Landsman May 2000
      Added XMID, YMID keywords to specify central position (default is still
          center of image) W. Landsman March 2002
      Recognize Galactic coordinates, fix Levels display when /PUTINFO set
          W. Landsman May 2003
      Correct conversion from seconds of RA to arcmin is 4 not 15.
      M. Perrin July 2003
      Fix integer truncation which appears with tiny images WL July 2004
      Changed some keyword_set() to N_elements WL Sep 2006
      Work to 1 pixels level when overlaying an image,added /OVERLAY keyword
        Use FORMAT_AXIS_VALUES() W. Landsman Jan 2008
      Make /OVERLAY always optional W. Landsman Feb 2008
      Check if RA crosses 0 hours WL Aug 2008
      Use Coyote Graphics WL Feb 2011

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