Research On Topology Repair Method Of Land Use Data Based On DBF Database

Land use data reflects the attributes and conditions of surface natural objects and man-made structures in geographical conditions,and it is an important part of national land surveys.The accuracy of the quality of land use data determines the reliability of the quality inspection system in land surveys.The quality of land use data directly affects the economic and social benefits of related fields.Therefore,in order to ensure the quality of land use data,while strengthening the quality supervision in the production process,it is necessary to strengthen the inspection of the topological relationship of the graphic data of land use patches and repair their topological errors,which will ensure the correctness.Based on Visual Studio 2015 software and C ++language,this paper analyzed the structural elements of the DBF database to design the file read,and common topological errors of land use data based on the DBF database for researching on repair methods.The main work is reflected in the following aspects:(1)Elimination of duplicate points in land use data.In this paper,according to the structural characteristics of land use patches,the types of repetitive points were divided into single patch repetitive points,island map repetitive points,and map repetitive points with the same starting point.The nodes of each patch polygon were detected separately,and the topology of the patch was combined.The relationship was to remove duplicate points that were smaller than the topological tolerance value.Through example data verification,compared with the grid algorithm for deduplication,the algorithm can improve the deduplication efficiency while ensuring the topological relationship of the original patch polygon.(2)A method for processing self-intersection of speckles in land use data was proposed.This paper mainly introduced the method of eliminating the discounted line segments in the self-intersection of the polygon.According to the rules of "in node" and "out node" in the return line segment,the boundary points of the polygon were unified.Based on this,the set of discounted line segments was judged by the cosine value of the boundary nodes,and the extra nodes in the discounted line segments were eliminated to eliminate the discounted line segments in the graph.(3)Automatically correction for the boundary of land use data.The node encryption processing and short-line elimination in the patch boundary were mainly performed to realize the automatic correction of the boundary.The node encryption was divided into single-pattern polygon encryption and island-pattern polygon encryption based on the types of patch polygons.The encryption values and encryption coefficients were set,the coordinates of the encryption points were calculated,and the border encryption was automatically performed according to the original topology.For the elimination of the boundary short line,the type of the short line was divided into three types: a single short line,a corner short line,and a stepped short line.According to the characteristics of the short line,the extension length and the extension coefficient were set,and the coordinate information of the extension point was calculated to eliminate the boundary short line.(4)The traditional Delaunay triangulation algorithm was improved,and a new method for unifying land use data boundary was proposed.In order to solve the “gap”and “fragment” problems caused by the overlapping or separation of adjacent patches in the national survey,and maintain the topological relationship between the patches,an improved triangulation algorithm was proposed for patches with inconsistent shared boundaries.Patch boundaries were automatically detected and corrected.Based on the principle of maximum and minimum angles and the principle of illegal edges,this algorithm used a quadrilateral-based method for triangulation,and automatically extracts and smoothes the skeleton lines between the patch buffer regions instead of the shared boundary to achieve the result of uniform boundary.Applying this method and the traditional Delaunay triangulation algorithm to the boundary unification of the land use data in the third national land survey respectively.The experimental results show that this improved algorithm can effectively solve the problem that the extension direction of the skeleton line in the Delaunay triangulation cannot be determined.Moreover,the new boundary generated can approximately fit the natural curved shape of the original boundary and maintain the topological consistency of the patch boundary.