Research On Multi-resolution Rapid Generation And Display Optimization Of Large-scale 3D Terrain

At present,3D terrain visualization technology has been widely used in many fields,such as military simulation operations,urban landscape planning,streetscape navigation and 3D games.With the rapid development of photogrammetry,satellite remote sensing and other technologies,the sampling accuracy of terrain data is getting higher and higher,and the data scale of terrain elevation data and image texture data has increased rapidly.However,because of the limited hardware level of the computer,this makes it difficult to implement real-time efficient rendering of large-scale 3D terrain visualization.In order to solve this difficulty,The key technologies for real-time navigation of large-scale 3D terrain visualization systems is studied,including multi-resolution organization management of large-scale 3D terrain data,real-time efficient scheduling strategies of terrain data and rendering optimization related technologies,and finally realizes real-time and efficient rendering of large-scale terrain data.The main research contents and research results of this paper are as follows.(1)The organization and storage management strategy of large-scale terrain data is studied.Through the research and analysis of the conventional multi-resolution pyramid model generation method,an improved multi-resolution pyramid model generation method based on the limitation of the size of computer memory is proposed,which realizes the multi-resolution organization of large-scale terrain data.In view of the shortcomings of file storage methods such as long search and positioning time and difficulty in sharing,an OCI-based external Oracle database storage method is proposed to implement the external storage and management of large-scale terrain data.The test results show that the data organization storage management method proposed can reduce the amount of data redundancy by 34%,reduce the preprocessing and storage time by 35.8%,and reduce the roaming response time by an average of 46%.(2)The real-time scheduling strategy of internal and external terrain data is studied.Through the research and analysis of the commonly used view-clipping strategies,an improved view-clipping strategy is proposed,which can reduce the time-consuming of view-slice cutting while achieving the same simplified rate as the common view-clipping strategy.In view of the different processing methods of DEM data and DOM data in rendering,the DEM data pre-fetching,unloading,positioning index strategy based on memory buffer and DOM data scheduling strategy based on critical distance are proposed.In order to ensure the dynamic balance between data scheduling and real-time rendering,a multi-thread mechanism is used to speed up the data scheduling process and respond to data requests of rendering.The test results show that the average scheduling time of the internal and external scheduling strategy proposed in this paper is only 0.13 s,which fully meets the requirement of human visual temporary retention time,and the roaming picture is very fluent.(3)The optimization of terrain scene rendering is studied.Through the analysis of the advantages and disadvantages of several common terrain rendering algorithms,a terrain rendering algorithm based on quad-tree structure is proposed and improved,including the use of triangular fan based grid structure and quad-tree subdivision based on double queues.In order to alleviate the contradiction between CPU,GPU and the data transmission speed of internal and external data,the two-level caching mechanism is proposed and the evaluation criteria of node refinement are redefined to improve the rendering efficiency.In order to enhance the reality of the terrain scene,the crack processing technology and texture mapping is studied,which greatly improves the authenticity of the terrain scene.(4)The design and development of large-scale 3D terrain visualization system.A large-scale 3D terrain visualization system is designed and implemented.It has functions such as data preprocessing and storage,grid mode display of terrain,texture mode display of terrain,thumbnail mode display,and real-time roaming.The system performance test results show that the visual system resources are reasonable and the rendering efficiency is high.The average roaming frame rate is about 118 Hz,which fully satisfies the requirements for smooth roaming.