GPoly:

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   Graphical interface to create a polygon.

   The user clicks with the mouse to create points on a polygon. When the
   last point is within the threshold of the first the polygon is
   determined to be closed.

   Since version 2014.1
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   Form:
   p = GPoly
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   Inputs
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   None

   -------   
   Outputs
   -------
   p       (2,:)   Matrix of polygon vertices

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