Transform between NAD 83 and ITRF or WGS 84

Model: NGS HTDP 3.6.0 14-parameter transformations through ITRF94, applied as HTDP does; WGS 84 (G2296, G2139, G1762) taken as ITRF2020, ITRF2014, and ITRF2008

Accuracy: Matches NGS HTDP 3.6.0 within 1 mm; the transformation itself is good to about 1–2 cm in the conterminous United States

When to use this: Use this whenever survey or mapping data in NAD 83 has to meet a GNSS position. Published US control, state plane coordinates, parcel data, and almost every official map are on NAD 83, while a receiver gives ITRF or WGS 84; the two differ by more than a meter in the conterminous United States, which is far too much to ignore and small enough to go unnoticed. Give the epoch the coordinates belong to. The answer includes the difference as a distance and an azimuth, so the size and direction of the discrepancy are visible rather than buried in the new numbers.

Limitations: The published transformation is itself good to about one to two centimeters in the conterminous United States, so the result cannot be better than that however many digits it carries; the arithmetic matches HTDP to a millimeter, which is a different claim. It changes the frame, not the epoch, and does not move a position along its plate's motion — that is the plate-motion tool, and the two are usually wanted together. NAD 83 (2011), (PA11) and (MA11) cover different plates and are not interchangeable: using the wrong one puts the answer out by meters. Unqualified WGS 84 is taken as the realization aligned with the ITRF of its day and says so, because a bare WGS 84 label does not identify a realization. Heights are ellipsoidal throughout, not orthometric, and nothing here touches a vertical datum.

Worked example: Kansas: WGS 84 (G2296) to NAD 83 (2011) in 2026.7. Source: NGS HTDP 3.6.0 compiled from htdp.f, menu option 4, and independently PROJ 9.3.0 through pyproj on EPSG:9988 to EPSG:6319, which agrees with the tool to 9.5 nanometres in latitude, 1.2 in longitude and 0.2 in height. 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: 26 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• Horizontal Time-Dependent Positioning (HTDP) software, version 3.6.0, National Geodetic Survey, NOAA, HTDP 3.6.0 (2025-04-07). Subroutine SETTP: transformation parameters from ITRF94 to NAD 83 and the ITRF and WGS 84 realizations.

Terms

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

NAD: North American Datum

The family of North American horizontal datums: NAD 27 on the Clarke 1866 ellipsoid and NAD 83 on GRS 80. Source: NADCON5 datum transformations

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