The first realization of SIRGAS (SIRGAS95) referes to ITRF94, epoch 1995.4. It is given by a high-precision GPS network of 58 points distributed over South America. In 2000, this network was re-measured and extended to the Caribbean, Central and North American countries. To account for this extension, the meaning of the acronym changed from the original “Sistema de Referencia Geocéntrico para América del Sur”, to the current “Sistema de Referencia Geocéntrico para las Américas”. The second realization (SIRGAS2000) includes 184 GPS stations and refers to ITRF2000, epoch 2000.4. The coordinate accuracy of these two realizations is about ±3 … ±6 mm.

The third realization of SIRGAS is the SIRGAS Continuously Operating Network (SIRGAS-CON). At present, it is composed by more than 200 permanently operating GNSS sites, 48 of them from the global IGS network. SIRGAS-CON is weekly computed by the SIRGAS processing and combination centres. The final coordinates and velocities are provided by the IGS Regional Network Associate Analysis Centre for SIRGAS (IGS-RNAAC-SIR) at DGFI (Deutsches Geodätisches Forschungsinstitut, Munich, Germany). The SIRGAS-CON constrained weekly solutions refer to the observation epoch and to the current ITRF, at present the IGS05, a realization of the ITRF2005. The coordinates of the multi annual solutions refer to a specified epoch, e.g. the solution SIR09P01 refers to IGS05, epoch 2005.0.

The activities related to the definition and realization of SIRGAS are coordinated by the SIRGAS-WGI: Reference System.

The relationship between the different SIRGAS realizations (or its densifications) is given by the transformation parameters between the corresponding ITRF solutions and the reduction of the coordinates to the same epoch. This reduction is carried out in two ways, alternatively: i) those continuously observing stations (SIRGAS-CON) which are operating for more than two years apply the velocities computed in the latest multi-annual solution of the IGS-RNAAC-SIR, and ii) those stations with velocities not known from the IGS-RNAAC-SIR solutions are reduced by means of the model VEMOS (Velocity Model for SIRGAS). The agreement between the different SIRGAS realizations at the same epoch is at the mm-level.