Robust Algorithm for Identifying the Orientation of Simple Polygons

Traditional cross product method faces the difficulty in identifying the orientation of simple polygons in the case that the included angle between two neighboring edges is near 0 or 180 degree, with their cross product close to 0, so that a wrong result may be generated. In this paper, a new method in distinguishing 0 degree case from 180 degree case is given, and a novel orientation identification algorithm is presented. In the case of 0 degree,the extreme vertex serial number comparison method is used to get the orientation. And in the case of 180 degree, the coordinate value comparison method is used to get the orientation. Experimental results show that the new algorithm is robust, and an improvement on the identification performance is achieved in comparison with the cross product method.