ITRS – International Terrestrial Reference System

The International Terrestrial Reference System (ITRS) is a globally defined, geocentric coordinate reference system with its origin at the Earth’s center of mass, axes oriented according to the Earth’s rotation, and scale defined in the framework of General Relativity. It provides the theoretical and conventional definition of a consistent, Earth-fixed reference system for precise positioning and geodetic applications.

In geodesy, the ITRS serves as the fundamental reference system for realizing global terrestrial reference frames such as the ITRF. It ensures consistency in station coordinates, velocities, satellite orbit determination, Earth rotation studies, and the integration of multi-technique space-geodetic observations (GNSS, VLBI, SLR, DORIS). The ITRS is defined and maintained under the conventions of the International Earth Rotation and Reference Systems Service (IERS).