Research on Applying the True 3-Dimensional Coordinate Reference System Based on the Ellipsoid to GIS

摘要

Map coordinate reference system (MCRS) is widely adopted in GIS, which is composed of projection coordinate system and elevation coordinate system. However, with the limitation of map projection, MCRS is not able to exactly and uniquely express the 3d location of any point of the globe. After analyzing MCRS' disadvantages for further development of GIS, this paper points out that geodesic coordinate reference system (B, L, H) (GCRS) can accurately express the 3d point of the globe based on the theories of geodesic survey. However, GCRS is not so much directly adopted in GIS because of the complex computation on the ellipsoid and the different units of GCRS' coordinate parameters. In order to overcome GCRS' disadvantages, this paper introduces a regional geodesic coordinate reference system (RGCRS) based on the ellipsoid, which is helpful to GCRS in GIS because of RGCRS' own characters. And more important, there is peer-to-peer relationship between RGCRS and GCRS. Furthermore, the paper presents a compound true 3-dimensional coordinate reference system by efficiently combining and integrating GCRS and RGCRS. GCRS can keep the data integrated and continuous, and ensure that spatial measure of large-scale region is exact, while RGCRS makes it easy and efficient to realize model, visualization and spatial analysis of GIS within a certain region. The significance of compound true 3-dimensional coordinate reference system is seen in that discarding the conventional map coordinate reference system, it breaks through the binding of map projection and realizes exact and unique expression of the 3d location of any point of the globe in GIS.