Separation of Contour Lines and Longitudinal and Latitudinal Lines and Contour''s Vectorization
地形等高线与经纬网的分离及其矢量化

Based on straight property of longitudinal and latitudinal lines in partical scope, contour lines are separated with them automatically, by taking advantage of property that average freeman chain code of straight line is equal to it's separate one, so as to realize automatic vectorization of contour lines.