The study of robust algorithm for orientation and point inclusion query for polygon in GIS

The polygon orientation identification and point-in-polygon query algorithm for GIS polygon is in the course of improvement. Robust algorithms are presented in this paper. By comparing the serial number of polygon´s four (or three, two) extreme points, the polygon´s orientation can be identified, the main computation in the new algorithm is only integers´ comparison. By finding the shortest point to subtense edge´s approximate distance of the query point to all the polygon edges, and comparing its´ cross product with that of a extreme point, the inclusion between the point and the polygon can be identified. The algorithms overcome the shortage of the past algorithms, treat the special cases as the ordinary ones. The algorithms´ time complexity and space complexity is linear to the number of polygon´s vertices. No special cases should be pay more attention to. They are easy to understand and straight forward to implement. Analyses show that they are robust, highly efficient.