The strategy adopted for the ITRF2008 generation consists in the following steps, illustrated in Figure 1.:
Apply minimum constraints equally to all loosely constrained solutions: this is the case of SLR solutions
- Apply No-Net-Translation and No-Net-Rotation condition to IVS solutions provided in the form of Normal Equation
- Use as they are minimally constrained solutions: this is the case of IGS and IDS weekly solutions
- Form per-technique combinations (TRF + EOP), by rigorously staking the time series, solving for station positions, velocities, EOPs
and 7 transformation parameters for each weekly (daily in case of VLBI) solution w.r.t the per-technique cumulative solution.
- Identify and reject/de-weight outliers and properly handle discontinuities using piece-wise approach.
The discontinuity files used for each one of the 4 techniques are found here.
- Combine the per-technique cumulative solutions adding local ties in co-location sites.
This last step yields the final ITRF2008 solution comprising station positions, velocities and EOPs.
Note that EOPs start in the early eighties with VLBI and SLR, while DORIS contribution starts from 1993
and GPS from 1997.0.