Study On The Visualization Of Multi-Source Geospatial Data

After more than 40 years' development in the field of GIS, two-dimensional GIS has matured and three-dimensional GIS has become a new tendency of development. The rapid developments in the capabilities of computing of computer graphics and hardware provide effective technical support for three-dimensional GIS. With the application of techniques, such as remote sensing and photogrammetry, mapping industry has continuously improved both the efficiency and quantity of getting information. Besides, the implement of project named "National Basic Mapping Installation", the construction of basic geographic information data base in Hubei Province has becoming more and more perfect. On the basis of theories, techniques and data above, it has important significance to realize three-dimensional visualization of Multi-Source Geospatial Data within large area.Being subsidized by the project named "Three-dimensional Information Roaming Inquiry System" from Hubei Geometrics Center, this thesis has made a deep research on the aspects of three-dimensional visualization of multi-scale, multi-data source, multi-resolution and seamless out-of-core Geospatial Data. Besides, this thesis made several researches on multi-resolution pattern plan of out-of-core Geospatial Data, summation of vector data, three dimension model building of landform, dynamic dispatching of landform data block based on ISAM and interactive operation of sphere, achievements of which has been made good use of to realize the development of central part of Three-dimensional Geographic Information Roaming Inquiry SystemResearch contents of this thesis mainly contain the following aspects:Firstly, the author made a detailed introduction of multi-resolution LOD model and provided arithmetic of LOD model based on quadtree. On the basis of the above methods, the author also made several pretreatments on DEM data and texture data by sphere quadtree, like layering and blocking, and then set up multi-resolution LOD model. What's more, the author also adopted an easy and intelligible coding method to organize and store the data after pretreatment, and made a detailed discussion on topological relations among those block data and treatment of boundary deformity data block.Secondly, the adoptions of geocentric coordinate system realized the construction of three-dimensional model based on Grid. During the transition course of each level of LOD model, the author made effective treatment on arisen shortage or loss of data block. In addition, different data sources were organized by layer while different kinds of sources adopted different rendering priorities. Moreover, in the process of usage, each rendering layers can be changed their orders to meet the practical need.Thirdly, the author stated that vector data shall be overlapped to the earth's surface by the same usage of sphere quadtree. As for the use of the same LOD model foundation rule, vector data and raster data has realized seamless integration, and such kind of phenomena appeared in the course of summation were eliminated.Fourthly, taking full advantage of limited computer resources, the author suggested adopting such kind of methods to reduce the number of objects involved in rendering and modeling, like data cutting on view frustum and layer setting on visible range. Moreover, the author also realized the dynamic dispatching of landform data block. By setting up reference for memorized data block, when needed to load new landform data block and the past memory had been default values, least recently used, LRU should be used to get rid of least recently used data block, and then new block should be loaded, or else directly loaded.Fifthly, the author adopted multithreading programming ideology and made the following works as daemon, such as the load and delete of data and construction of model. It not only promised a better interaction and higher real-time, but also made operations fluently such as flying, roaming and positioning.Sixthly, the author made an approach to animation technique of stimulation of three-dimensional scene. Frame-by-frame animation has been realized after coping with the free time in program and renewing the thread design.Seventhly, the author adopted quaternion to make the sphere rotate, made researches on rendering, zooming and flying of three-dimensional scene all over the earth, which made GaeaGlobe have good operability. On the basis of researches above, the author implemented a large area data in the central part of three-dimensional rendering inquiry system by C#.NET,XML,Direct3D, existing functions including the construction of three-dimensional scene, data loading, control of layer, three-dimensional rendering, flying of circuit, drawing and management of line, accession and administration of label, inquiry and location of essentials in DLG layers.As time is limited, development of more functions of system is also on the way. However, in the process of realizing projects, the author found that the good expandability of system was guaranteed completely depending on the mode of object-oriented, which provided full support for system's further improvement and function extension. Along with the perfection of system, it has great significance to push researches on three-dimensional visualization in large area and applications of Hubei Basic Geographic Information.