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The Network Transmission and Visualization of Three-dimensional Terrain Model

Author: YangZeDong
Tutor: JiangNan
School: Nanjing Normal University
Course: Cartography and Geographic Information Systems
Keywords: Network applications Terrain rendering real-time transmission TerrainVisualization
CLC: P284
Type: Master's thesis
Year: 2013
Downloads: 43
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Abstract


SAAS (Software as a service) is a new software application mode released in the21st century. In this mode, users can accomplish software operation only through a browser. Application in network is a prerequisite for SAAS, goal of which is to achieve network transplantation of efficient and stand-alone edition terrain visualization algorithm, and this will be of great significance for the construction of digital cities based on SAAS mode. Compared with network2D maps, network3D terrain scenes have several advantages such as its symbols are easy to understand and vivid. But SAAS of network3D terrain visualization develops slowly, limited by some difficulty like large amount of terrain data, time-consuming in terrain data transmission and client plug-in and so on. Response to the difficulty mentioned above, this thesis has done the following jobs:Firstly, the terrain rendering algorithm has been studied, especially the Geoclipmap, which is current mainstream and efficient stand-alone edition, In this algorithm framework, the amount of data of each layer of LOD (Level of Detail) is controllable and regular, and it is advantageous not subject to the amount of terrain data. Based on the feature of regular nested grid of Geoclipmap, this article aims to design a novel GeoClipmap coordinate system and frustum culling mechanism which is suitable for network transmission. According to the original point of Clipmap, the client can make use of this coordinate system and frustum culling mechanism to reconfigure X, Y coordinates of terrain meshes rapidly. Compared with the conventional method which transfers the data structure of full terrain vertexes, the method in this article achieved a certain effect which has8times compression ratio better than ever.Secondly, with regard to the real-time transmission of terrain model, this research extends and designs WebSocket data frame structure from bottom, puts the WebSocket to Real-time transmission with terrain grid data. By Extending data frame structure, this article achieve the real-time transmission of the terrain data through the unit of Clipmap layer. In addition, this research makes full use of the superiority of WebSocket:simpler protocol handshake mechanism, smaller data packet header, to reduce model transmission time and increase the amount of transmitted3D model data. Thirdly, this research has devised a new way to build a triangle strip for the client terrain rendering in the situation of no need to install any plugins. When Terrain mesh data is transmitted to the client, system automatically added two degenerate triangles at the beginning and end of the each triangle strip, and then converted the whole square grid to one triangle strip, which further improves the terrain rendering speed.Through the research on the above three aspects, the design in this article realized a prototype system which has visualization and terrain transmission with browser-oriented and no-need-to-install plungins, verifying the feasibility of the GeoClipmap in algorithm network transplantation. In this prototype system, the amount of transmission data of each layer of LOD, a255×255terrain mesh, decreases from0.49M to0.06M, the amount of data experienced a87.8%reduction, and experienced a51%reduction respect to GeoClipmap algorithm, which greatly improves the speed of the client terrain visualization.

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CLC: > Astronomy,Earth Sciences > Surveying and Mapping > Cartography ( Cartology ) > Topographic map - based
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