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    Draw circle(s) of specified radius at specified position(s)


    If a position is not specified, and device has a cursor, then a circle
    is drawn at the current cursor position. By default, TVCIRCLE now
    (since Jan 2012) assumes data coordinates if !X.crange is set.

Calling Sequence

    TVCIRCLE, rad, x, y, color, [ /DATA, /FILL, _EXTRA = ]


    RAD - radius of circle(s) to be drawn, positive numeric scalar

Optional Input

      X - x position for circle center, vector or scalar
      Y - y position for circle center, vector or scalar
              If X and Y are not specified, and the device has a cursor,
              then program will draw a circle at the current cursor position
      COLOR - color name or intensity value(s) (0 - !D.N_COLORS) used to draw
              the circle(s). If COLOR is a scalar then all circles are drawn
              with the same color value. Otherwise, the Nth circle is drawn
              with the Nth value of color. See cgCOLOR() for a list of color
              names. Default = 'opposite' (i.e. color opposite the

Optional Keyword Inputs

      /DATA - if this keyword is set and non-zero, then the circle width and
              X,Y position center are interpreted as being in DATA
              coordinates. Note that data coordinates must be previously
              defined (with a PLOT or CONTOUR call). TVCIRCLE will
              internally convert to device coordinates before drawing the
              circle, in order to maintain optimal smoothness. The default
              is to assume data coordinates if !X.CRANGE is set. Force
              device coordinates by setting DATA = 0 or /DEVICE
      /DEVICE - If set, then force use of device coordinates..
      /FILL - If set, fill the circle using cgCOLORFILL
              Any keyword recognized by cgPLOTS (or cgCOLORFILL if /FILL is
              set) is also recognized by TVCIRCLE. In particular, the color,
              linestyle, thickness and clipping of the circles are controlled
              by the COLOR, LINESTYLE, THICK and NOCLIP keywords. (Clipping
              is turned off by default, set NOCLIP=0 to activate it.)
              If /FILL is set then available keywords are LINE_FILL and




      (1) Some round-off error may occur when non-integral values are
          supplied for both the radius and the center coordinates
      (2) TVCIRCLE does not accept /NORMAL coordinates.
      (3) TVCIRCLE always draws a circle --- even when in data coordinates
          and the X and Y data scales are unequal. (The X data scale is
          used to define the circle radius.) If this is not the behaviour
          you want, then use TVELLIPSE instead.


      (1) Draw circles of radius 9 pixels at the positions specified by
          X,Y vectors, using double thickness lines
          IDL> tvcircle, 9, x, y, THICK = 2
          Now fill in the circles using the LINE_FILL method
          IDL> tvcircle, 9, x, y, /FILL, /LINE_FILL


          The method used is that of Michener's, modified to take into account
          the fact that IDL plots arrays faster than single points. See
          "Fundamental of Interactive Computer Graphics" by Foley and Van Dam"
          p. 445 for the algorithm.

Revison History

          Original version written by B. Pfarr STX 10-88
          Major rewrite adapted from CIRCLE by Allyn Saroyan LNLL
          Wayne Landsman STX Sep. 91
          Added DATA keyword Wayne Landsman HSTX June 1993
          Added FILL keyword. R. S. Hill, HSTX, 4-Nov-1993
          Always convert to device coords, add _EXTRA keyword, allow vector
          colors. Wayne Landsman, HSTX, May 1995
          Allow one to set COLOR = 0, W. Landsman, HSTX, November 1995
          Check if data axes reversed. P. Mangifico, W. Landsman May 1996
          Use strict_extra to check input keywords W. Landsman July 2005
          Update documentation to note NOCLIP=0 option W.L. Oct. 2006
          Make all integers default to LONG W. Landsman Dec 2006
          Use Coyote Graphics procedures W. Landsman Feb 2011
          Default to data coordinates if !X.crange present WL Jan 2012
          Add /DEVICE coords, fix Jan 2012 update. Mar 2012

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