A CONSISTENCY CORRECTION OF SHARED BOUNDARY AFTER POLYGON GENERALIZATION

T. Ai

Wuhan University

tinghua_ai@tom.com

The consistency of spatial data is one of important characteristics in spatial data quality. The map data processing usually leads to the inconsistency question. Map generalization will destroy the original spatial relations due to the operation aiming at the independent object, and a post-correction is usually required to maintain the spatial relation, to keep the consistency between neighbour objects. The consistency correction of shared boundary between adjacency area objects is a typical example after the polygon generalization.

In the process of adjacent polygon generalization and integration, neighbor polygon overlay is not able to strictly guarantee topological consistency but generate series of fragment area and gap area in overlap region. For polygon map data, such as land-use, vegetation, and soil class, the boundary should be consistent and all polygons should cover the whole region with neither gap nor overlapped area..

To correct the inconsistency between polygon boundaries, this paper offers different solutions based on spatial neighbor relation analysis. Three cases of inconsistency are distinguished : intersecting, separating and interlacing. Intersecting inconsistency causes small fragment area and separating inconsistency causes small gap area. Correction of inconsistent shared boundary is to find single line which can approximate original two boundaries with high location precise. Considering the different importance of two neighbor polygons locating beside corrected boundary, we provide two correction approaches: less important polygon to snap its neighbor, and equal polygons to move together to adjust their shared boundary. So 3 x 2 methods need to be separated. This study implements Delaunay triangulation model to detect inconsistent area among shared boundary, and further uses triangulation skeleton to produce common boundary. Through triangle stripping operation, the inconsistent area can be extracted as set of triangles, like a sausage. Skeleton construction of sausage area has properties of simulating common boundaries well and the problem space will be evenly separated into two neighbor polygons. In order to access single skeleton axis line (not tree structure), the study discusses the reason of producing hair branch and based on the triangle class characteristics presents one method of removing invalid triangle in sausage area. According to 6 cases in the consistency correction, the Delaunay triangulation based method has to handle different corrections. The full paper will discuss the methods respectively with 6 algorithm experiments.