Research On Adaptive Simplification Of Administrative Boundaries Based On Visvalingam-Whyatt Improved Algorithm

With the development of science and technology and the popularization of mobile electronic devices,the use of electronic maps has also continuously affected people ’ s daily travel and life.However,under the current limited bandwidth conditions,it is inevitable to compress the massive geospatial data with increasing volume in visualization.Among them,the compression of the boundary vector data of administrative divisions is often applied to the fields such as the infinite scale of electronic maps.The compression of vector data is often realized by point thinning with some broken line simplification algorithms.However,the traditional broken line simplification algorithms such as Douglas-Peucker algorithm and Visvalingam-Whyatt algorithm are prone to topological alienation such as self-intersection when compressing the boundary vector data of administrative divisions.Some improved algorithms based on traditional algorithms can solve the problem of self-intersection to some extent.However,it cannot meet some more complex requirements such as the multi-level expression required by the boundary vector data of administrative divisions in practical application,and the consistency of topological relations between adjacent edges.This paper compares the compression effect of Douglas-Peucker algorithm and VisvalingamWhyatt algorithm on the boundary vector data of administrative divisions.Combined with some special requirements that the boundary vector data of administrative divisions need to meet in the compression process,an improved algorithm based on Visvalingam-Whyatt algorithm is proposed.The algorithm is based on the comparison between the triangle area formed by each continuous three points of linear elements in the data and the set threshold value for point thinning.The following points are improved :1.By calculating the triangular parameters of each node and the monotone chain cutting,the extreme points and the monotone chain nodes in each linear element are extracted as the feature points to retain,which not only avoids the self-intersection in the graph to a certain extent,but also solves the problem of other topological alienation such as adjacent intersection that is prone to occur in the vector data of administrative divisions,and maintains the topological consistency of the graph before and after the vector data compression and the geometric characteristics of the contour.2.Different thresholds are set for different levels of administrative divisions to conduct hierarchical compression and retain more feature points in the national boundary.Iterative compression is used to further reduce the generation of topological alienation,and vector data with different levels of compression rates are obtained more efficiently.The multi-level expression in the visualization process of administrative division boundary geographic data is realized.3.In the compression process,some specific restrictions are set and programmed according to the drawing requirements of administrative division boundary line,which makes the compression more reasonable.The paper has 30 pictures,12 tables,and 128 references.