Why change from NAD83 to the International Terrestrial Reference Frame (ITRF)?


The change to CIGD11 which incorporates ITRF is considered to both simplify and standardize the Cayman geodetic control and mapping system.

  • ITRF positions are more widely used than NAD83. Most global and national mapping projects use and produce data referenced to an ITRF realization and not NAD83.
  • ITRF05 positions are considered identical to those referenced to WGS84(G1150).
  • The currently used reference frame NAD83(CORS96) is optimized for use in the conterminous United States and differs from WGS84 and ITRF by up to 2m.
  • By removing one reference frame (NAD83) many geodetic tasks will be simplified as only a single reference frame and a single set of transformation parameters will need to be considered.
How big is the change?

The difference between the NAD83(CORS96) datum and the ITRF05 datum in our area is the equivalent of approximately 1ft in easting and 1ft in northing. However the ellipsoid heights vary by nearly 6ft.

Global and National Mapping

ITRF is the chosen reference frame of most countries around the world; it is a global framework of reference stations representing the most accurate realization of the WGS84 datum, i.e. the ground reference stations are more numerous and the positions of both the ground reference stations and the satellites more accurate than previous realizations.

Example National Geodetic Datums
Nation Datum Name Base Reference Frame
Australia Geodetic Datum of Australia - GDA ITRF92(1994.0)
New Zealand New Zealand Geodetic Datum 2000 - NZGD2000 ITRF96(2000.0)
UK European Terrestrial Reference System - ETRF89 ITRF89(1989.0)
USA North American Datum 1983 - NAD83 NAD83(CORS96) (2002.0)
Cayman Islands Cayman Islands Geodetic Datum 2011 – CIGD11 ITRF05(2011.0)