Establishment of Geodetic Coordinate Systems - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 374

conditions for China to construct its own new geocentric coordinate frames (see
Wei 2003; Ning 2002).

Definition of the CGCS2000

The new generation national geodetic coordinate system in China is the China
Geodetic Coordinate System 2000, abbreviated as CGCS2000 (see Chen 2008;
Yang 2009). Its definition is consistent with that of the CTRS, namely:

1. Origin: coincides with the center of mass of the whole Earth including oceans
and atmosphere
2. Orientation: initially given by the BIH orientation at 1984.0
3. Time evolution (of the orientation): to create no residual global rotation relative
to the crust
4. Unit of length: the international standard meter, defined in a local Earth frame in
the meaning of a relativistic theory of gravitation

The reference epoch of CGCS2000 is at 2000.0.
The reference ellipsoid of CGCS2000 is the CGCS2000 Reference Ellipsoid,
whose defined parameters are shown in Table 4.1 . The normal ellipsoid is consis-
tent with the reference ellipsoid.
Several points need to be addressed:

1. Of the four constants of the CGCS2000 Reference Ellipsoid, three constants are
coincident with GRS80, namely a, f, and .GMis the value recommended by

IERS, and most of the other geocentric ellipsoids in the world are the same.
2. There is a slight difference between the values a and f of CGCS2000 and the
higher-precision

ˉ

values recommended by IERS (a ﾼ 6, 378, 136.6 m,

298.25642), but this will have no effect on applications.
3. The CGCS2000 Reference Ellipsoid differs slightly from WGS84 only in the
flattening f (which generated 1 mm error of the terrestrial coordinates at the
equator). These two ellipsoids can therefore be considered practically coincident
with each other.

1/f ﾼ

Realization of the CGCS2000

The CGCS2000 is realized by estimates of the station coordinates and velocities at
three levels.

Level 1: Continuously Operating Reference System (CORS). These constitute
the fundamental frame of CGCS2000 with an accuracy of a few millimeters in
coordinates and 1 mm per annum in velocity. The CORS also provide coordinate
datum for static and dynamic positioning and navigation.
GPS CORS are permanent ground-based observation stations that are
designed to provide long-term and continuous tracking and receiving of GPS