The strategy adopted for the ITRF2005 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 and DORIS solutions
- Apply No-Net-Translation and No-Net-Rotation condition to IVS solutions provided under the form of Normal Equation
- Use as they are minimally constrained solutions: this is the case of IGS 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 if necessary cumulative solutions of a given technique into a unique solution: this is the case of the two DORIS solutions.
- Combine the per-technique combinations adding local ties in co-location sites.
This final step yields the final ITRF2005 solution comprising station positions, velocities and EOPs.
Note that EOPs start in the early eighties with VLBI, SLR and DORIS contribution starts on 1993
and GPS on 1999.5. The quality of the early VLBI EOPs is not as good as the combined EOPs starting on 1993.