Research And System Implementation Of Vectorization On Geographic Objects In The Grid Map

Extraction and recognition of the geography information is the basis of geographic information system(GIS) and global position system(GPS). The vectorization of grip maps has become one of the main methods of getting digital information. After studying some typical map vectorization methods, the author realizes a map vectorization software, RasToVec, with Visual C++ programming language to recognize and capture the geographic elements in the grid maps.The current prevalent vectorization method based on thinning algorithm is adopted in the paper. Firstly, words labels in the scanned gray map are separated from the map as its gray rank is different from the other objects' in the map. Then the gray map is transformed into binary map by maximal threshold variance method. Noises in the binary map are filtered and geographic elements' edges are extracted by morphology. In the process of thinning the image, a new thinning method based on labeling is put forward. Compared with the traditional thinning algorithm, this method avoids the node distortion and map topology changing.In the process of vectorization, the node area and connected segment are abstracted according to the whole topology of map. The connected segment is transformed into its vector form by genetic algorithm(GA). The longest expended principle is used to combine the vector segment, and then the nodes are ensured and the last vector list is got. Besides GA, Douglas-poiker method is used in the process of vectorization and the comparison of these two methods in efficiency and precision is presented in the end. The erasing pixels process after thinning and segments coding avoids re-recognition and complexity, so the speed is improved.At present the research on vectorization is mainly among the engineering images. The method proposed in the paper satisfies the demand of GIS and realizes the interface with software MapInfo. The experimental results show that this method can reestablish the map's topology and get a good performance in precision and efficiency. This paper presents certain significance and application value in the field of GIS.