SIRGAS (Geocentric Reference System for the Americas) as reference system is defined identical  to the International Terrestrial Reference System (ITRS). Its realization is a regional densification of the global International Terrestrial Reference Frame (ITRF). The reference station positions are associated to a specific (reference) epoch and their variation with time is taken into account by discrete station velocities or by a continuous velocity model, which comprises tectonic plate movements and crustal deformations. Realizations or densifications of SIRGAS associated to different reference epochs and referring to different ITRF solutions materialize the same reference system and, after reducing their coordinates to the same frame (ITRF) and reference epoch, they are compatible at the mm-level.

The SIRGAS geodetic datum is defined by the origin, orientation and scale of the SIRGAS (ITRS) system and the geographical coordinates are derived by applying the parameters of the GRS80 ellipsoid.

The extension of the SIRGAS frame is carried out by national densifications of the continental network, which serve as local reference frames.