6CROMLEY R G. Hierarchical Methods Of Line Simplification[J]. Cartography and Geographic Information Systems, 1991,18(2) : 125 - 131.
7Douglas D.H. & Peucker T.K. Algorithms for the Reduction of Points Required to Represent a Digitized Line or Its Carricature[ J]. Canadian Cartographer, 1993, (10) : 112 - 122.