[ncl-talk] add a circle on a plot

[grace]

Hi,all:    I am wondering how to add a circle on a plot?
    For example,I want to indicate a round area on a drawn plot,take A（130°E，45°N）as the origin，40km as radius.How to add a such circle on a drawn plot like gsn_add_polymarker


   Do NCL have such function?
   Or do you guys have some advice?
     any information will be appreciated‍
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