Local Tie

A local tie is a precisely measured three-dimensional vector that connects the reference points of different space-geodetic instruments co-located at the same observatory site (e.g., GNSS antenna, VLBI antenna reference point, SLR telescope, DORIS beacon). Local ties are typically determined through high-precision terrestrial surveying techniques.

In geodesy, local ties are essential for combining observations from different space-geodetic techniques into a consistent terrestrial reference frame, such as the ITRF. Accurate local tie measurements ensure that technique-specific solutions are correctly aligned at co-location sites, improving the stability, scale, and long-term consistency of global reference frame realizations.