Necessity and Feasibility for a Geocentric 3D Coordinate System Employed in China
CHEN Jun-yong(State Bureau of Surveying & Mapping, Beijing 100830,China)
So far the Chinese modern geodetic datum as concerned, the focus is whether the geocentric three dimension (3D) coordinate system should be employed in China or not. As a matter of fact it is essentially a problem of necessity and feasibility for a geodetic coordinate system updating in a large developing country like China. The following topics in necessity are discussed: The situation and problems in Chinese existing geodetic coordinate system and its frame; The characteristics of a Chinese modern geocentric 3D coordinate frame; The advantages for a geocentric 3D coordinate system if it is employed in China. What kind of the Geodetic Fundamental Constants should be taken for a Chinese modern geocentric 3D coordinate system.The feasibility is the key point for updating a Chinese coordinate system. Only two among the four issues concerning the feasibility are discussed. One is that a Chinese geocentric 3D coordinate frame with enough points, suitable density, high accuracy, and dynamic is the necessary condition to realize the Chinese geocentric 3D coordinate system; The other one is the influences on the current existing millions various Chinese maps, especially the topographic map, caused by the change of the coordinate systems. Such as the changes of latitude, longitude, and Gauss plane coordinates of the surface points and their projection on the map, as well as the variation of the orientation and the length of the lines between the points on the map (including map outlines).