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GM_Surface whose exterior boundary shall be encoded counter-clockwise and any interior boundary encoded clockwise.
(A link to a web site that provides a simple method for testing if a polygon is encoded clockwise or counter-clockwise: http://stackoverflow.com/questions/1165647/how-to-determine-if-a-list-of-polygon-points-are-in-clockwise-order.)
For aeronautical data, this implies that the outside perimeter and any eventual holes shall be encoded as shown in the figure below. This rule might be difficult to apply strictly on short term as existing aeronautical systems require data to be encoded in clockwise direction. For example, the Operating Procedures for Aeronautical Dynamic Data (OPADD)
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