Vector Polygon Overlay
T.J. Harding, R.G. Healey, Sara Hopkins, S. Dowers · 2020
This chapter aims to explore how parallel methods can be applied within the different stages of the operation, and how these different stages fit into the overall modular design scheme set out. The overall process involves: While Intersect proceeds with the plane sweep algorithm, it passes processed geom and node data to topology building, stitching and output (TSO), which undertakes: Therefore Intersect only requires geoms. When Intersect has found all the intersections between input geoms and output nodes have been formed, new output polygons can be built. Each output polygon comprises the intersection of two input polygons and thus it is given two attribute values, one from each parent, in the usual manner. The functions to perform these tasks are discussed in detail in the chapter on TSO. A typical polygon overlay algorithm assumes that input maps contain lists of geoms with associated edge records and that the output map requires suitably derived geom and edge records, together with associated face and area records.