A Progressive Method of Simplifying Polylines with Multi-bends Simplification Templates

Polyline simplification is one of the most important and classic researches in multi-scale expression of cartography and GIS. Polyline simplification methods based on bend units get widespread attention recently. Having analyzed the bends composing characteristics and the manual simplification process of polylines, it is resonable to find that not all of invisible bend units are deleted directly. A new progressive simplification method based on multi-bends groups is proposed. Firstly, based on the threshold of the simplified scale, polylines are divided into multi-bends groups. Secondly, in order to avoid over-simplification, some reasonable bends deletion options which called multi-bends templates are proposed. However multi-bends templates is not steady and always related to the quantity of multi-bends uniquely. Considering of the minimal errors derived form polyline simplification, the best multi-bends template that result in the least displacement is selected to simplify muli-bends groups. Thirdly, polylines do not stop repeating the above two steps until all bend units of simplified polylines can be detected in the simplified scale. Experiments with real road-net data were implemented, and comparison with other algorithms is discussed. Results show advantages including: (i) The proposed algorithm is a progressive simplification process which is conform to human cognition. (ii) The proposed algorithm can preserve the main shape of the polyline with deleting invisible bend units enough. (iii) The proposed algorithm avoid unnecessary displacement by deleting bend units as little possible.

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