SINEX

SINEX, short for Solution INdependent Exchange, is a standard text-based format used in geodesy to exchange estimated geodetic solutions between analysis centers, data centers, and users. It is designed to capture the results of network and site coordinate solutions, including station positions, velocities, and the associated covariance information, in a way that supports mathematical combination and datum transformation. SINEX is widely used in GNSS processing and is a core component in coordinating realizations of global terrestrial reference frames such as the ITRF.

A SINEX file typically contains a header with metadata, one or more solution blocks enumerating the estimated parameters, a block describing a priori information and constraints, a section defining the reference frame, and a covariance matrix for the parameters. It may also include a list of stations with metadata and optional constraints to enable alignment to a common frame. The format explicitly supports both constrained and unconstrained solutions and preserves the relationship between parameters through the covariance information.

Usage and significance: SINEX enables exchange and combination of independent solutions from different analysis centers, facilitates archiving and reproducibility, and supports the realization and comparison of terrestrial reference frames such as the ITRF. By carrying full covariance information and constraint details, SINEX allows users to reweight, constrain, or re-reference solutions without reprocessing raw observations.

History: SINEX was developed in the 1990s as a standard within the geodetic community, and it has been maintained and widely adopted by international organizations including the International GNSS Service (IGS) and networks contributing to the ITRF. It remains the de facto standard for exchanging geodetic network solutions.