Research On Fractal Law And Automatic Generalization In Multi-scale Line Features

The primary goal of the construction of national spatial data infrastructure is to build a multi-scale vector map database.The multi-scale representation of maps can provide basic information for the development of many fields,and cartographic generalization is an important means to achieve this technical problem.Our country is facing the challenge of upgrading the traditional static multi-database and multi-version geographic information vector database to the dynamic one-database multi-version model,which involves how to integrate the vector elements of different sources and different scales(scale).And the use of mapping theory and methods to achieve the goal of "stepless scale",that is,to enable vector data to adapt to the change of scale and compress spatial data to achieve reproduction the real geographic space in the best way.This process involves the selection of the content of geographical elements,the transformation of the quantitative relationship between the new scale and the original scale spatial data,and the graphic generalization of geographical features in the new scale spatial data.Map fractal theory provides mathematical support for solving these problems.Fractal theory is born in geoscience,and fractal dimension can quantitatively describe the shape complexity of vector line objects.therefore,the multi-scale expression model of vector line features can be constructed with the help of the characteristics of fractalIn this paper,the multi-scale expression of vector line features is studied by combining fractal theory and OptCor(Algorithm Optimum Correspondence)method:for the original line network data of map,dynamic logic segmentation is carried out according to the principles of river classification and reason classification,and a ranking table of importance degree is established for the classified line features.In order to realize the cross-scale change of line features,the quantitative law of line features selection is discussed by combining fractal theory of river network and road network and mapping square root law,and the ground elements are screened on the basis of importance ranking table.For each independent line features after screening,it is necessary to simplify the line features according to the requirements of cartographic generalization.in this paper,the classical D-P algorithm is selected,and the multi-scale change formula of line features is derived based on the fractal theory.The multi-scale representation of line features is realized by using D-P algorithm with automatic threshold selection,and it is proved that D-P algorithm itself is a method to measure the fractal characteristics of line features.Finally,a homonym point matching method based on OptCor algorithm is proposed,which can be used to synthesize multi-scale line features and generate intermediate scale line features by "interpolation".The purpose of this method is to use multi-database and multi-scale homonym data to improve the accuracy of the data.The research of these theories and methods will provide important theoretical support for automatic synthesis and construction of multi-version spatial database.