Study On Method Of Expressing Earth Object In Large Based On Ellipsoid Surface

By the effects of traditional cartography, almost all of the digital maps and GIS are the traditional map projection theory, due to the earth ellipsoid to the plane projection transformation, the direction of the inevitable emergence of location and size and other aspects of deformation. Traditional map projection as the mathematical basis of their spatial frame of reference, which for a particular purpose, local scale is feasible. But when the area range from small regional expansion for large regional or global scale, the traditional projector can not meet the continuous multi-resolution digital earth and comprehensive uses, this time using the map projection mathematical basis for the space will bring many problems.As traditional map projection theory in the expression of a large regional or global scale digital maps and GIS are many problems existing at the time, the thesis first proposed and discussed ellipsoid digital maps and the concept and advantages of electronic map. Theoretical expression of the traditional map projection reference surface object of thought, this paper presents the use of projection surface expression of the idea of the object surface ellipsoid and on the basis of the ellipsoid on the electronic map rendering, display and analysis of the basic method. As ellipsoid surface expression of the object based on the absence of the plane through the ellipsoid to the projection, thus avoiding the projection distortion, effective solution to a large regional or global scope of the expression of digital maps and GIS issues, effectively expanding the electronic maps and digital map analysis functions and applications.In this paper, the concept of electronic map ellipsoid, geodetic coordinate described by the location of geographical entities and ellipsoid positioning and calculation, geographic entities portrayed space Cartesian coordinates in three-dimensional graphics and spatial orientation and calculation. That the view three-dimensional Cartesian coordinate system of space, metric space is still earth coordinate system, using the nested themes coefficient method the calculation of the earth, earth map coordinates will be mapped to the Cartesian space, using OPENGL the specific implementation. This will not only ensure the realization of three-dimensional visualization, but also to ensure the accuracy of measurement of space.