Conclusions of the discussion concerning new parameters for Earth orientation and proposal

A comparison of the parameters considered above shows that Euler's angles (described in (iii)) or equivalently the celestial coordinates of the z-axis of the TRS (described in (viii)), which reduce to three the number of EOP, do not use any intermediate pole and consequently include both high frequency and low frequency components of the motion of the z-axis of the TRS wrt the CRS.

The other parameters separate the celestial components from the terrestrial components according to a ``frequency criteria'' using an intermediate pole. Such a procedure facilitates the estimation of the parameters from observations, unless the model for low frequency motion in space is perfect.

The difference between the use of a geometrical origin (as $\Sigma$ or $K$ for examples) and a kinematical origin ($\sigma$) is that, in the first case, the instantaneous rotation of the considered origin is included in the derived value for the Earth's angle rotation, whereas it is clearly separated when using directly $\sigma$ as the origin on the moving equator.