Establishment of Geodetic Coordinate Systems - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 350

Fig. 7.7 The motion
trajectory of the
instantaneous pole relative
to CIO from 1 July 2010 to
1 July 2013. Source: IERS
The point at which the prime meridian and the equator intersect is designated as the
origin of longitude worldwide for longitude determination. Since 1957, a number of
observatories with good long-term stability have been used internationally to
maintain the longitude origin. Averaging the origin of longitude reversely obtained
from the original observatory longitude values adopted gives the mean observatory
longitude origin. After the CIO was defined as the Earth's polar origin in 1968, the
meridian that passes through the CIO and the mean observatory longitude origin is
called the initial meridian. The 0 longitude defined by various new technologies is
made, as far as possible, coincident with the initial meridian, yet there still tends to
be an error of less than 1 00 .
Reference System and Coordinate System
To describe the state of an object, such as determining the position of a particle, or
describing the law of motion of a particle or body of mass (the Earth or a satellite), a
reference system must be selected, without which discussions about laws of motion
make no sense.
A coordinate system differs from a reference system in that it is always used to
describe the mathematical representation and attaches more importance to the
mathematical meaning, whereas a reference system is more concerned about the
reference rather than the mathematical representation, and physical meaning is
highlighted. For instance, establish an Earth-fixed reference system with its origin
at the Earth's center of mass (terrestrial reference system). In this reference system