how to draw a circle wrapping a few points

Dear NCLers,
For several curves plotted by gsn_xy, I want to draw,say, an empty circle to
wrap a few points in the former. I checked up with the ncl-talk archive, seems, to draw a marker of cycles can do this.
However, that needs much tuning of the radius of the marker (circles, here) to do it.
Are there any simpler methods in NCL to do this?
Your help is appreciated.
Best,
Ting Lei
                                               

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Received on Sat Jul 27 16:47:38 2013