Research On Error Recognition And Correction Of Vector Elevation Data Based On Hierarchical Grid Index

Terrain is one of the most important elements of physical geography.The research and application of topographic information science have been fully developed.Traditional topographic maps used to be produced and accumulated in large quantities for infrastructure construction,national defense construction and other purposes.At the early stage,they were mainly stored in paper form.The emergence of digital topographic maps and the maturity of scanning digital technology have enabled a more scientific management of historical topographic maps.The traditional topographic map is the main way to record the topographic information in the early stage,which contains a lot of historical elevation information,which can effectively extend the time series of topographic research,and is conducive to the in-depth excavation of the long-term law of topographic change.However,elevation error reduces the quality of vector elevation data and restricts the practical application of elevation information.The improvement of the quality of vector elevation data needs a lot of manpower and time.The research of historical elevation data mining and data integration put forward higher requirements for the automation degree of quality improvement of vector elevation data.To solve the quality problem of vector elevation data with high efficiency and precision is an important support for historical data mining and research work.In this paper,the digital topographic map data covering Youyang county in Chongqing were selected to extract the vector elevation data.The elevation errors in the contour and elevation data were counted and sorted out,and the distribution and quantity characteristics of the errors were analyzed,which were taken as the basis of the algorithm design,and the data of some map sheets were selected as the verification data of the algorithm accuracy.Based on the analysis results,a hierarchical grid index model at the edge of the map sheets and a hierarchical grid index model inside the map sheet are created respectively,which reduces the repeated calculation of data and improves the efficiency of the algorithm significantly.By further refining the error types and combining with the spatial characteristics of vector elevation data elements,the algorithm design of error recognition and correction is more targeted,and the work of elevation error recognition at the edge of contour map sheets,elevation error recognition inside the contour map sheet and elevation point-line contradiction recognition is completed.At the same time,based on the sheet edge contour spatial orderliness strong characteristics,the contour spatial location label and quick sort algorithm are used to construct the strong spatial position relationship to solve the accuracy problem of contours matching at the edge of map sheets.And the elevation conflict site is used as a driving factor to make logical judgments on contours,thus enabling the recognition and correction of elevation errors.The main research results of this paper are as follows:(1)The spatial distribution characteristics of elevation errors in vector elevation data are statistically analyzed,which provides a focus for quality improvement.(2)The hierarchical grid index was applied to the elevation error recognition and correction process of vector elevation data,and the applicable model inside and outside the map was built,which effectively reduced the problem of repeated data operation in the calculation process,reduced the calculation time,and significantly improved the efficiency of the algorithm.(3)The recognition of contour elevation errors and the contradiction between elevation points and contours was completed.At the same time,the correction of contour elevation errors at the edge of map sheets was attempted,and the accurate positioning and correction of contour elevation errors at the edge of map sheets was realized by building strong spatial position relations.The results show that: In the vector elevation data,the elevation errors of contour data are mainly concentrated near the map boundary,and the elevation errors within the map are relatively few,accounting for less than one fifth of the errors.The spatial distribution of elevation errors at elevation points has strong randomness.The application of hierarchical grid index effectively shortens the computation time of the algorithm and significantly improves the computation efficiency.The method presented in this paper can effectively identify and correct contour line errors at map junction and identify contour errors inside of map sheet and elevation point-line contradictions.Compared with existing methods,the method presented in this paper has better performance in accuracy and efficiency,and provides a new idea and method support for improving the quality of vector elevation data.