Transform between ITRF and WGS 84 realizations

Model: IERS ITRF2020 → past-ITRF Helmert parameters (epoch 2015.0, with rates), chained through ITRF2020; WGS 84 realizations taken as coincident with the ITRF each was aligned with

Accuracy: The IERS parameters; a few millimeters between ITRF2020, ITRF2014, and ITRF2008, and up to centimeters for older realizations

When to use this: Use this when two positions are quoted in different realizations of what people loosely call the same system. A GNSS network gives coordinates in a particular ITRF, a receiver may report WGS 84 without saying which realization, and archived survey data carries whichever was current when it was observed; combining them without this step buries a shift of centimeters to decimeters in the result. Give the epoch the coordinates belong to, because the frames move relative to each other over time and the parameters carry rates. It reports the shift in meters and as east, north, and up, so the size of what would otherwise be silent is visible.

Limitations: This changes the frame, not the epoch: it does not move a position forward or back in time along its plate's motion, which is the neighbouring plate-motion tool, and the two are usually needed together. Unqualified WGS 84 is treated as the realization aligned with the ITRF of its day and says so in a warning, because a bare WGS 84 label does not identify a realization. The parameters are the published IERS values, so the answer is as good as they are — a few millimeters among ITRF2020, ITRF2014, and ITRF2008, and up to centimeters for the older realizations — and none of that accounts for the accuracy of the coordinates themselves. It is a rigid transformation of the whole Earth and knows nothing about local deformation.

Worked example: Pittsburgh from ITRF2020 to ITRF2014 in 2026. Source: PROJ 9.3.0 through pyproj, transforming EPSG:9988 (ITRF2020) to EPSG:7912 (ITRF2014) with PROJ's own EPSG-sourced parameters at epoch 2026.72: latitude 40.44611101524038 and longitude -79.98222202049854 identical in every digit, height 300.0011211372912 m against 300.0011211390832 m, a difference of 1.8 nanometres. It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.

Review: Not yet independently reviewed by a geodesist.

Last verified: 2026-09-19, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Checked against: 25 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• ITRF2020: transformation parameters from ITRF2020 to past ITRFs, IERS ITRF Center, IGN France, Transfo-ITRF2020_TRFs.txt. Parameters at epoch 2015.0 with rates, position-vector convention (formula 1).
• Department of Defense World Geodetic System 1984, NGA.STND.0036, National Geospatial-Intelligence Agency, NGA.STND.0036_1.0.0_WGS84. Chapter 2: realizations of WGS 84 and their alignment with the ITRF.

Terms

ECEF: Earth-centered, Earth-fixed

Cartesian X, Y, Z coordinates in meters from Earth's center, turning with the Earth. X points to 0° longitude on the equator and Z to the North Pole. Source: Department of Defense World Geodetic System 1984

GRS: Geodetic Reference System

An Earth ellipsoid defined by the IUGG. GRS 80 underlies NAD 83 and is almost identical to WGS 84. Source: Geodetic Reference System 1980

ITRF: International Terrestrial Reference Frame

The global scientific reference frame, realized from thousands of stations whose motions it models. ITRF2020 is current. Source: ITRF2020 transformation parameters to past ITRFs

WGS: World Geodetic System

The US Department of Defense global reference frame and ellipsoid that GPS uses; the current version is WGS 84. Source: Department of Defense World Geodetic System 1984