The International Terrestrial Reference Frame (ITRF) is a series of globally defined datums developed by the International Earth Rotation and Reference Systems Service (IERS). The ITRF serves as the standard framework for a wide range of applications and is crucial for various positioning-based activities such as mapping, 3D modelling, and GIS. ITRF allows us to determine a consistent coordinate in the format latitude (Φ), longitude (λ), ellipsoidal height (H), and time (t).
A geodetic datum is a reference system that defines how positions are represented. This includes:
- a coordinate system
- a reference ellipsoid
- additional models, such as a deformation model.
The ITRF is a globally recognised reference system that provides precise and consistent coordinates for points on Earth's surface. The ITRF aims to achieve accuracy, reliability, and internal consistency over time with a clear and defined datum specification for origin, scale, and orientation.
To achieve these goals, the ITRF incorporates a time series of station positions and earth orientation parameters from various space geodesy techniques. These include global navigation satellite systems (GNSS), satellite laser ranging (SLR), very long baseline interferometry (VLBI), and doppler orbitography and radio-positioning integrated by satellite (DORIS).
The ITRF is linked with the International Terrestrial Reference System (ITRS), a theoretical framework that defines regulations and conventions for creating reference frames suitable for measuring Earth. The ITRS is realised through different ITRF solutions, each new solution adds new data and the latest advancements in mathematical and surveying methods. These realisations support satellite navigation systems like GPS, GLONASS, Galileo, and BeiDou.
The ITRF is essential for understanding long-term Earth system processes such as tectonic deformation and climate change indicators. It is not a useable geodetic system by itself but is an accurate realisation of the Earth’s terrestrial reference frame for a specified reference period. The ITRF is then used to establish a national, regional or global datum.
| Name | International Terrestrial Reference Frame yy (or yyyy)* *where yy denotes the year up to which datasets were used in the realisation of the datum |
|---|---|
| Abbreviation | ITRF(yy) or (yyyy)* |
| Coverage area | Worldwide, between 180°W –180°E and 90°N – 90°S |
| EPSG code | Varies for each realisation |
| Coordinate system | Geographic |
| Reference frame | Earth-centred, Earth-fixed |
| Reference ellipsoid | Typically GRS80 but may vary between realisations |
| Prime meridian | Greenwich |
| Deformation model | Post-Seismic Deformation included from ITRF2014 onward for GNSS reference sites with major earthquakes |
| Reference date | There are multiple realisations of ITRF, with each of these a separate datum. High accuracy coordinates must state the realisation the coordinates are referenced to. |
| Datum realisation | Implementation date | Reference epoch | Network (absolute) accuracy (m) (1-sigma) relative to ITRF2008 |
|---|---|---|---|
| ITRF94 | 1997 | 1993.0 | |
| ITRF96 | 2000 | 1997.0 | |
| ITRF97 | 1 July 2002 | 1997.0 | |
| ITRF2000 | 5 January 2001 | 1997.0 | |
| ITRF2005 | 28 January 2006 | 2000.0 | |
| ITRF2008 | 28 April 2009 | 2005.0 | When compared to ITRF2005, better than 0.01 |
| ITRF2014 | 29 January 2016 | 2010.0 | When compared to ITRF2008 and ITRF2005, better than 0.01 |
| ITRF2020 | 2 October 2022 | 2015.0 | When compared to ITRF2014, ITRF2008 and ITRF2005, better than 0.005 |
Read more information about transforming ITRF coordinates to NZGD2000