Consistency Constraints For Collapse Operation Method In Land-use Map

Land use map is a thematic map reflecting the spatial distribution, quantity,quality and structure of land use in a certain area. Similar to general geographic data,land-use data contains both spatial data and attribute data, and the polygons in the land-use spatial data have the characteristics of seamless spatial coverage, land-use attribute data enriched by semantic information and multi-level thematic characteristics, etc. Therefore, the map generalization of land use data is different from the traditional ways. In addition to traditional cartographic theory factors,it also needs to consider the characteristics of land use data such as topology consistency and semantic consistency. To date, great effort has been dedicated to land use data generalization operation algorithm. However, most of existing algorithms focus on aggregation and amalgamation in land use data generalization, and little has been done on collapse.Based on previous studies, this work takes into account the characteristics of land use data, and examines the methods of polygon collapse into line in land use data.The main research includes: (1) Exploring the topological changes after land use polygons collapse based on the space point set topological theory, and analyzing the equivalencies of topological relationship for polygon and polygon, polygon and line,line and line; (2) Introducing the quantitative description method for the long narrow polygons, and proposing a method of long narrow polygon detection and parts of long narrow tributary division based on the constraint Delaunay triangulation algorithm; (3)Proposing a method to detect topological sharing point based on circle extension, and different consistency correction methods is given for the different topological changes after long narrow polygon collapse. At last, experimental algorithm modules as well as the proposed methods are designed and implemented in Visual Studio 2010.Finally, this work carries out five experiments, including scattered small polygon amalgamate, long narrow polygon automatic detection, part of long narrow polygon divided, skeleton extraction, consistency correction. The original data is 1:5000 land use map in Chunxi town, Gaochun District, Nanjing, of which the target scale is 1:50000 scale. The experimental results show that the scattered polygons are amalgamated, and four types of polygons are collapsed into line. The area is basically balanced between two different scales, which reflect the validity of the proposed consistency correction algorithm. The experimental results demonstrate the effectiveness and feasibility of the proposed methods in this work.