Research On Nonlinear Local Transformation For Vector Map Based On Feature Points

With the development of information technology, Geographic Information System (Geographic Information System, GIS) is widely used in many fields. GIS is a computer information system which is specialized for managing the distributed data of geographical space. Digital map is an important part of GIS. The vectors map is used in the overwhelming majority of GIS.The development cycle of vector map is very long,the production costs of vector map is extremely high, the liquidity of vector map is strong and the confidentiality of vector map is weak. The development of vector map refers to National Information Security. Some correlation processing of map must be done to ensure its safety such as doing coordinates obfuscation to the key elements of the map geographical information can prevent hostile forces doing precision strike to the marked places of the map, the review and permission from the relevant administrative department of surveying and mapping must be acquired before the publication of a map, therefore, the research on nonlinear local transformation for vector map is very significant. How to use the vector map in a safe and efficient way and construct a useful geographic information system on this basis have been an important subject of today's study.The local transformation of vector map is an algorithm which does reversible nonlinear transform to the map while the map maintains with the same topological structure, the algorithm of vector map's nonlinear local topologic transformation, which is combined with topological transformation and space projection technique, is based on feature points, it has better irreversibility while comparing to these typical algorithm which guarantee the vector map with the same topology. Two nonlinear transformation models are presented in this article, each model represents the nonlinear transformation as one kind of a small distortion to the area of rubber in the "rubber conversion", so this local transformation algorithm of map is like doing extension and expansion to the rubber, this random combination of transformation models which is used in the confidentiality of the vector map makes better use of "rubber conversion". The algorithm for doing local transformation to the vector maps does special treatment to the key points, the offset of the key points is not less than the minimum required offset.The experimental results shown that the irreversible algorithm not only effectively guaranteed the same topology of the vector map, but also did good effect to the vector map for local transformation, the algorithm has good practical value.