Skip Navigation Links > Home > Data Themes > Global Geodetic Frame

Global Geodetic Reference Frame

The Global Geodetic Reference Frame (GGRF) is the framework which allows users to precisely determine and express locations on the Earth, as well as to quantify changes of the Earth in space and time. It is not a data theme in the sense of the other themes, but it is a prerequisite for the accurate collection, integration and use of all other geospatial data.

Why is this theme fundamental?

Geospatial data is collected using diverse measurement and observation techniques, with varying levels of accuracy, and observed at different times. When this data is referenced to a Geodetic Reference Frame it obtains higher levels of usability, interoperability and therefore potential use. It allows the data to be confidently reinstated or integrated, and projected through time for use at a different epoch.

Which sustainable development goals (SDGs) will it help to meet?

Wherever geospatial data is used to contribute to a SDG, the Geospatial Reference Framework is an inseparable part. Geospatial data is most important to SDGs 2, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16.

Geospatial data features in more detail

The GGRF includes, but is not limited to: products that provide realisations of the international celestial and terrestrial reference frames (ICRF and ITRF); the component technique observing systems, data centres, analysis centres, and combination and product centres; gravimetric products and physical height systems; and the physical infrastructure and services that allow access to the Reference Frame.

The International Terrestrial Reference System (ITRS), the ICRF and the ITRF are the fundamental geospatial data features for a Geospatial Reference Framework. An ITRS is a spatial reference system that is co-rotating with the Earth. In such a system, positions of points anchored on the Earth’s surface, together with continuous and episodal observations, define geospatial coordinates which undergo only small variations with time. The ITRF is a set of physical datum points with precisely determined coordinates in a specific coordinate system attached to the ITRS. Such an ITRF is said to be a realization of the ITRS. The rotation of the Earth is measured with respect to a frame tied to stellar objects, the ICRF.

Earth Orientation Parameters (EOP) connect these two frames together. Four main geodetic techniques are used to compute accurate coordinates; Global Navigation Satellite Systems (GNSS), Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS).

Many nations have national coordinate reference systems (Datums) for application within their country. Increasingly these national systems are being closely aligned to the ITRF which allows interoperability between data collected on these national datums with coordinates derived from GNSS systems.

Possible sources of data
  • International Earth Rotation and Reference Systems Service (IERS): establish and maintain the ICRF and the ITRF.
  • International GNNS Service (IGS): collects, archives, and distributes GNSS observation datasets.
  • International VLBI Service (IVS): data required for the determination of the ICRF, the ITRF, and EOP.
  • International Laser Ranging Service: weekly station coordinates and daily EOP estimates.
  • International DORIS Service (IDS): reference frame station coordinates and velocities, satellite orbits, geocenter motion, and EOP.
  • Many national governments and some private corporations: provide access to real-time and post-processed GNSS data streams and Satellite-Based Augmentation Systems (SBAS).
Existing Data Standards
  • International and National Standards covering coordinate reference systems. The IERS has a range of conventions that contain models, constants and standards.