Contour Line Of Pretreatment Technology,

Topographic contour line is one of the key tasks in GIS development.The conversion of maps from paper into digital, namely map-vectorization is very important. In topographic maps, contour lines are the most important features to characterize three-dimensional terrain on two-dimensional map sheets, so its pretreatment of the contour line is in urgent. In this paper an effective method for extracting contour lines from color scanned topographical maps is proposed. This paper takes color emphasizes map with a scale of 1:5000 as the research on the recognition and acquisition of contour line.Firstly, color model, its conversion is discussed thoroughly, the data of color map image is studied carefully and the color characteristic of color map image is induced thoroughly. The algorithm of color separation is researched earnestly and valued rightly. At last ,the new method is put forward to: the method based on RGB color model and image spatial relativity to get the result we want.Aiming at the characteristic of contour lines, an analysis and improvement of the Zhang fast parallel thinning algorithm is presented, considering both the symmetry and operating speed, and an adaptive algorithm of contour lines thinning is brought forward.The brown map that includes contour lines has many conglutinations and ruptures due to the map own quality, scanned effect, overlay of other map objects. Because of the bad quality of contour line map, the work of contour lines extraction and recognition from color map becomes very hard. Achieving the thinned contour lines of lined constituents, the adoption of tracking method based on varying step lengths not only reduces the searching times, but also makes the contour identification more precise. When encounters broken point, the step length increases automatically to span it. At the same time enables the tracking and compressing to be simultaneous.Finally ,the research work in this thesis is concluded .status and development of the map digitalization are described.