Research On Construction And Visualization Of Global Multi-resolution Half-honeycomb Trapezoid Grid

Because of the characteristics of traditional latitude/longitude graticule, for instance, spatial inequality, uncertain adjacency relations, etc., the disadvantages, as high-redundancy and inadequate-precision, is shown clearly while being used as the basic data structure for the visualization of global topographic data. Therefore, a large number of discrete global grid systems have been constructed. The triangle grid has more complicated adjacency relations though it has a simple structure. Meanwhile, the hexagonal grid is a subdivision unit with spatial equality, best compactness and unique adjacency relations. And the applications of single-resolution hexagonal grid have already been started. However, under the limitation of its subdivision performance, the brilliant geometric properties are not able to be widely used for multi-resolution grids. In order to break through the limitation, a new subdivision unit, Half-honeycomb Trapezoid, is proposed. Based on the summarization of the geometric properties and subdivision performance of Half-honeycomb Trapezoid, a new discrete global topographic grid system is established, and its compatibility with hexagonal grid is analyzed. At last, the visualization of multi-resolution global grid is achieved.The main work of this dissertation goes as follow:1) A new subdivision unit, Half-honeycomb Trapezoid is proposed. Then the multi-resolution global grid and its file structure are constructed based on Half-honeycomb Trapezoid.As a subdivision unit of the discrete global grid, half-honeycomb trapezoid has excellent geometric properties, simple calculation of subdivision, and good compatibility with hexagon. In order to prove the possibility of using Half-honeycomb Trapezoid as the subdivision unit, the properties are summarized. Then the adjacency relations in trapezoid grid are discussed, as the proof of its compatibility with hexagonal grid. Based on the relations among subdivision levels, first, the address coding system for the multi-resolution global grid is established. Second, the relations between address code and adjacency of trapezoid grid are discussed. Third, rules of translation between trapezoid grid and hexagon grid are summarized. At last disciplines of chunking and file format are in the precision of at least 3 seconds.2) A set of visualization algorithms for global trapezoid grid is explored. Based on the data structure of global trapezoid grid, the LOD (Level of Detail) method is localized for trapezoid grid. And the caching algorithm and data engine are established. After that, the improvement of the terrain rendering for trapezoid grid is researched. And then, in order to solve the blankness of common visualization methods, a real-time rendering algorithm of ocean surface is proposed.3) With the results of prototype implemented by us, compares among trapezoid grid, hexagon grid and latitude/longitude graticule are carried out, which proved that trapezoid grid has satisfactory compatibility with hexagon grid, and better spatial equality than latitude/longitude graticule.