A reference frame (or geodetic reference frame) is a precisely defined coordinate system that provides the mathematical and physical foundation for specifying positions on Earth’s surface. Reference frames establish the origin, orientation, and scale of coordinate systems, enabling consistent and accurate position determination across different locations, times, and measurement systems, essential infrastructure for all precise positioning, surveying, and geodetic applications.

Reference frames are realized through networks of physical points (geodetic monuments, reference stations) whose coordinates are determined through extensive measurement campaigns using GNSS, VLBI, SLR, and other geodetic techniques. The coordinates of these reference points, published with associated uncertainties and velocities, constitute the practical realization of the reference frame definition. Users align their measurements to the reference frame by connecting to these control points or by using correction services whose coordinates are defined within the frame.

The distinction between global and regional reference frames is important for practical applications. Global frames like the International Terrestrial Reference Frame (ITRF) provide the most accurate worldwide coordinate system, accounting for tectonic plate motion through station velocities. Regional frames like NAD83 (North America), ETRS89 (Europe), or GDA2020 (Australia) may be fixed to specific tectonic plates or tied to particular ITRF realizations, simplifying coordinate use within their regions but potentially diverging from global frames over time.

Proper reference frame management is critical for high-precision GNSS applications. Different GNSS constellations broadcast ephemerides in their own reference frames (WGS84 for GPS, PZ-90 for GLONASS, GTRF for Galileo, CGCS2000 for BeiDou), which are maintained compatible with ITRF but may have small systematic differences. Correction services specify their reference frames and epochs, and users must ensure consistency when combining data from multiple sources. Errors from improper reference frame handling can reach centimeters to meters, entirely negating precision positioning capabilities.