A Design for Polygon Overlay Algorithm in the Simple Feature Model

Most of the vector overlay operations are designed in the vector-topological model, which require the individual layers structured with full topology. It takes rather a long time to build the topology to each of the input data sets, and the output of the process is a new topological structured layer whose topology information seldom needed. In order to avoid the time-consuming topology building process and improve the efficiency of the vector overlay operations, some GIS platforms developed the spatial analysis operations making use of the OGC simple feature specification. The paper describes the vector overlay operations in simple feature model and takes the polygon intersection operation as an example to illustrate the design and implement of our algorithm. The main problem during the polygon overlay operation is the spurious polygons and 'coastline weave', which tends to arise when two lines are overlaid which are actually slightly different versions of a same line. The paper adopts an effectual decision strategy in line-intersection algorithm to provide a better solution to both the accuracy and efficiency of it, through focus on the problem of the successive entry-point or exit-point and the repeated intersection points, and the alternative searching of the intersected polygon. Performance tests show the presented polygon overlay algorithm provides good analysis performance in GIS, and this design lead to a better performance than the algorithm based on the topological model especially when the data quantity goes to large.