A Study Of The Theory And Algorithms Of Discrete Global Grid Data Model For Geospatial Information Management

In recent years, a number of data structures for global geo-referenced data sets have been proposed based on the regular, multi-resolution grid. This dissertation presents a study of the most promising of such systems, which we call spherical Discrete Global Grid Systems (DGGS). The majority of the research includes generating algorithms of spherical grids, evaluation criterions of spherical grids, digital expression of spherical grid cell, and multi-resolution hierarchical management of grid cell. The followings are what we have done in this dissertation:1. The traditional square grid is expanded from a plane to a sphere, and the Spherical Tiled Quad Tree (STQT) data model is put forward to represent global remote sensing image and terrain data. Based on the TIFF and XML open stands, the data management scheme is implemented and some core techniques of real-time terrain simplification and display on the surface of sphere are proposed.2. A new research method that first confirms edges of icosahedron on a sphere is introduced so as to describe the theory of the Snyder equal-area map projection for polyhedral globes systematically in an easy way. Then the strict transforming formulas and detailed algorithms are provided in order to improve precision. Furthermore the length and the angle deformation of the projection on a signal face are analyzed.3. In order to get spherical equal-area grids, a versatile algorithm that generates triangle, diamond and hexagon grids is implemented. Two criterions, including the ratio of maximum cell edge to minimum edge and the mean squared deviation of cell perimeter of all spherical grids are examined with experiments. The result indicates that both criterions of all grids are convergent and H4-CI grid fits for multi-resolution geographic information management among them.4. The Quarternary Triangle Mesh (QTM) structure based on spherical cell vertexes is offered so as to construct the sphere digital space for multi-resolution data management with it.5. To overcome the serious error-coding problem of Cavalcade Approach Method (CAM), a new translation method between QTM code and longitude/latitude coordination is introduced in a 3-axes coordinate system.6. Based on the searching algorithms of sub-cell which are advanced, the culling method and level of detail display algorithm are studied. Then the experiment proves that this method is correct.7. The dilation algorithm of Voronoi diagram based on H4-CI grid is studied. The result of experiments indicates that the algorithm suits for point sets, arc sets and curved surface sets, and has high precision.8. Instead of ellipsoid, almost all kinds of DGGs are based on spheres at present. And they do not meet the high precision need of many applications. To solve this problem, the dissertation establishes four corresponding relationships between sphere and ellipsoid, by which DGG is projected from the former to the latter. Also, it derives deformation expressions of length, angle and area caused by latitude changes. At last, the paper analyses distributions and rules of deformation with the result of experiment.9. Two experimental systems, GlobalView and GridView, are designed and implemented using VC++ and OpenGL. The former is a multi-thread global massive terrain management system.