All grids referred to below are available from the ICSM GitHub transformation grid repository in the widely used Canadian National Transformations version 2 (NTv2) format and provided under CCBY 4.0.
GDA94 ⇔ GDA2020
ICSM is currently developing two 2D national transformation grids:
- Conformal: simply a grid version of the 7 parameter similarity (Helmert) transformation: the basic difference between GDA94 and GDA2020 coordinates primarily due to plate tectonic movement (approximately 1.7m NNE over 26 years); and
- Conformal + Distortion: incorporates the conformal 7 parameter transformation plus localised and regional distortion revealed by incorporating coordinates on ground survey control networks across the nation.
When produced, the grids will be downloadable from the ICSM GitHub transformation grid repository.
The appropriate NTv2 transformation grid to use differs depending on the jurisdiction and the accuracy and lineage of the dataset being transformed. Basic recommendations are listed in Table 3.4 of the Geocentric Datum of Australia 2020 Technical Manual, but if in doubt individual jurisdictions should be consulted for specific advice.
AGD66 ⁄ 84 ⇔ GDA94
Initially, state and territories produced individual NTv2 transformation grids. These files transformed from either AGD66 or AGD84 to GDA94, depending which version of AGD was previously adopted by that jurisdiction. Subsequently, combined grids were produced and ultimately two national transformation grid files (one each for AGD66 and AGD84) were developed.
Transformation file A66 National (13.09.01).gsb provides a complete national coverage from AGD66 to GDA94. In NSW and Victoria, the on-shore and close coastal areas of the earlier combined State grid were included in the national grid, but elsewhere there may be differences. These differences are generally small but may be larger near the state borders and in areas where there was little or no common data (such as offshore). The AGD66 national file also covers the offshore areas out to the Exclusive Economic Zone (EEZ). Although still in NTv2 format, a simple conformal transformation was used to generate the shifts in these offshore areas.
Transformation file National 84(02.07.01).gsb has coverage for the states that previously adopted AGD84 (Queensland, South Australia and Western Australia). This coverage was produced by merging individual Queensland, South Australian and Western Australian transformation files, and differs slightly from the previous state files only near the merged borders.
These grids are available from the ICSM GitHub transformation grid repository.
- Consultant’s report to ICSM on the development of the national AGD66/84 ⇔ GDA94 transformation grids - February 2002