Published online by Cambridge University Press: 12 April 2016
The underlying method of forming the adopted Fundamental Reference System is the compilation of observations referred to some (independent) well defined coordinate systems. If the observations themselves are used to define the independent coordinate system, they may be used to help establish the Fundamental System. If the observations are differential, they may be used to refer star positions to the Fundamental System and/or smooth systematic irregularities within the Fundamental System.