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      Draw a line with a specified starting point, length, and angle

Calling Sequence

      one_ray, xcen, ycen, len, angle, terminus, /NODRAW ]

Input Parameters

      xcen, ycen = starting point in device coordinates, floating point
      len = length in pixels, device coordinates
      angle = angle in degrees counterclockwise from +X direction

Output Parameters

      terminus = two-element vector giving ending point of ray in device

Optional Keyword Input Parameters

      /nodraw if non-zero, the ray is not actually drawn, but the terminus
              is still calculated
        Any valid keyword to cgPLOTS can also be passed ot ONE_RAY. In
        particular, COLOR, THICK, and LINESTYLE control the color, thickness
        and linestyle of the drawn line.


      Draw a double thickness line of length 32 pixels from (256,256)
      45 degrees counterclockwise from the X axis
      IDL> one_ray, 256, 256, 32, 45 ,term, THICK = 2
  PROCEDURE: straightforward matrix arithmetic

Modification History

    Written by R. S. Hill, Hughes STX Corp., 20-May-1992.
    Modified to work correctly for COLOR=0 J.Wm.Parker HITC 1995 May 25
    Added _EXTRA keywords to PLOT W. Landsman November 2006
    Work with Coyote Graphcis W. Landsman February 2011

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