Study On Compression Algorithm For Vector Data In Geography Digitization

Because of the limitation of grid map, the vectorization of map is inevitable developing trend. In vectorization software EasyMap, there are many redundant points in elements of topographic map after tracing. In order to reduce store room and increase handling speed, it is necessary to compress the data of vector graph after tracing. The paper studies data compression of some special vector graph in the geography digitization.The paper mainly researches data compression of vector graph-rectangle, circle, ellipse, polygonal line and contour line after tracing. Few people studies data compression of them. So the paper studies the data compression of rectangle According to the basic principle of Hough transfer and graphic feature of parallel subtense and vertical adjacent side of rectangle and also studiesthe data compression of circle on the basis of graphic feature of circle. The average of coordinates of all discrete points in circle is coordinate of the center of circle. The vector data compression is realized using antithesis point method and main axis mode method. Not only there are lots of elements of topographic map of polygonal line in the map, but also few people in and out of our country study them. Although Hough transferring is a valid tool which examines the line, it is difficult to examine many lines because to define one line in accordance with parameter of it is a hard problem. So it is very need to find a new algorithm. The paper finishes the data compression of polygonal line with chain code algorithm of extracting feature point of curve and peak distance method suggested by this paper. Many people in and out of our country research vector data compression of curve. The main algorithms are: method of limited vertical distance, method of limited angle, Douglas-Peucker method, optical fence method, predicted method of vector data compression of curves. They have their advantages. But there are a lot of limitation with them. In all,the number of data compression is big after tracing and accordingly it studies the data compression of contour line based on B spline curve and small wave.Vector data compression is an important part of data processing in geography information system. It carries vital significance in map database establishment and geography environment simulation.