Research On Geographic Object Model And Key Technologies Based On Discrete Global Grid System

The discrete global grid system directly divides the earth's surface,which avoids various deformations caused by map projection,and can uniformly express,manage and analyze geospatial data of any range and scale in the earth,and is effective frame for integrating multi-source heterogeneous data.However,the expression and management of geographic objects that are relatively independent,has always been a difficult problem in the field of discrete global grid research.Therefore,this paper takes the object conceptual model as the highest level abstraction,and uses the multi-resolution hierarchical characteristics of the discrete global grid system to design a gridded object model that expresses and stores geographic objects.Then,in order to correctly and efficiently integrate the existing object data expressed by the vector data model in the gridded object model,this paper studies the fast transformation algorithm of geographic coordinates and grid codes,and vector data gridding method that maintains topological relationship.The research contents and conclusions of this paper mainly include:(1)Multi-resolution gridded object modelBased on the discrete global grid system,this paper makes full use of the multi-resolution hierarchical characteristics of the grid system,and designs the corresponding multi-resolution logic expression model according to the characteristics of point,line and polygon objects.Through the grid cell relationship and related code operations,the coded compression representation of the grid cell enumeration set is realized,and the physical storage model of saving storage space is realized based on the logical expression model.Experiments show that compared with the traditional model,the gridded object model has certain advantages in both storage space and computational efficiency.(2)Fast transformation algorithm of geographic coordinates and grid codesBased on the variation law of grid geometry,this paper proposes an efficient hybrid conversion strategy.The traditional recursive approximation method is adopted in the lower subdivision level where there exists a large difference in the geometric properties of the grid,and the direct mapping method with high efficiency is used in the higher subdivision level where the geometric properties of the grid are virtually the same.Experiments show that under the premise of ensuring the transformation accuracy,the fast transformation algorithm has significantly improved the transformation efficiency compared with the traditional method,thus accelerating the efficiency of integrating the existing geospatial data in the discrete global grid system.(3)Vector data gridding method that maintains topological relationshipBased on the existing gridding method,this paper finds the objects whose topological relationship have changed according to the spatial relationship between the grid cells,and then increases the geometric expression resolution of these objects through the multi-resolution hierarchical characteristics of the grid system,thus repairing all kinds of topological relationship changes caused by vector data gridding.Experiments show that this method can effectively maintain the topological relationship between the original vector data,and the data volume does not increase too much,thus ensuring the correct integration of vector data in the discrete global grid system.The research results show that the multi-resolution gridded object model can effectively reduce the disk space occupied by storing geographical objects while taking into account the computational efficiency.Fast transformation algorithm of geographic coordinates and grid codes,and vector data gridding method that maintains topological relationship,realizes the efficient and correct integration of traditional GIS vector data on the gridded object model.The gridded object model and related integration methods of this paper,can provide a unified and accurate expression,processing and management method for large-scale,multi-resolution and massive geographic object data.