Fig. 2 shows an example representing the differences between the three solutions for station CAGL (Cagliari, Italy) for which both IGS and EPN ZTD are available.
The top plot shows the differences between U.Porto and IGS ZTD while the bottom plot shows the corresponding differences between the U.Porto and the EPN product.
The bottom plot in Fig. 2 is representative of the pattern of the differences presented by most of the EUREF stations.
These differences may present various irregularities over the analysed period, which coincide with epochs when a change occurred in the processing at the EUREF analysis centres. On the contrary, the U.Porto and IGS solutions were calculated using the same methodology throughout the whole period, thus being homogeneous. On November 4, 2006, a major change occurred in the EUREF processing, leading to a substantial decrease of the differences from that date onwards.