Design Of High Precision Geographical Information System And Key Technologies For Islands Based On Cesium

China is a big ocean country with thousands of islands.Traditional geographical information technology can no longer meet the needs of users for visual expression of island geographic and spatial data,and WebGIS is one of the current research hotspots in the field of geographical information systems(GIS),and its advantages of cross platform and visibility can be fully used in the construction of island geographic information system.In this thesis,based on the open source Cesium framework,the key technology and system design of island oriented high-precision WebGIS are deeply discussed and studied,and the corresponding solutions are proposed.The main content and results of this thesis are as follows:(1)Scale-adaptive viewshed analysis algorithm based on visual continuity and alternation.Starting from traditional algorithms,this thesis proposes a intervisibility analysis algorithm based on visual continuity and alternation and a scale-adaptive terrain viewshed analysis algorithm.By adopting an effective reuse strategy in the continuous terrain on the LOS profile,the visibility of the previous point judges the visibility of the current point in order to reduce a lot of calculation redundancy and better improve the efficiency of the algorithm.When the distance between the LOS profiles exceeds the DEM accuracy,a new profile terrain analysis is added to improve the visibility sampling accuracy of viewshed analysis.In this thesis,the algorithm is implemented based on the island WebGIS environment established by the Cesium framework.Experimental test results show that this algorithm can greatly improve the computational efficiency of viewshed analysis while ensuring accuracy,and can perform efficient in terrain viewshed analysising with large-scale data.(2)Three-dimensional terrain path planning based on improved A* algorithm.Based on the analysis of the classic A* algorithm,this thesis proposes an improved algorithm for 3D terrain path planning based on the A* algorithm.The slope and distance are used as the index of the A* algorithm evaluation function,and the slope threshold is designed to meet the requirements of walking and climbing.There is a steep slope in the planning results,the actual cost function and the estimated cost function are optimized,the evaluation function is dynamically weighted,and the open list data structure is optimized to further improve the efficiency of the algorithm.In this thesis,the algorithm is implemented based on the island WebGIS environment established by the Cesium framework.Experimental test results show that the algorithm can efficiently search and plan a path with a gentle slope and the shortest distance in an island's complex terrain environment.(3)Design and implementation of the high-precision island WebGIS system architecture and key technology modules based on Cesium.Based on the Cesium framework,this thesis uses Java Script language and adopts B/S architecture and modular development ideas to design and implement the basic architecture and main functional modules of the island geographical information system,including real-world roaming,distance and area measurement,slope and aspect measurement,profile analysis and other routine operations,as well as the characteristic functions of key technologies such as viewshed analysis and path planning.This thesis verifies the performance of the designed and implemented functions through experimental tests,and achieves the basic goals of the design.