Difference Between GDA94 and GDA 解説
Analyze the 1.8-meter tectonic shift between Australia's GDA94 and GDA2020 datums. Explore the legal, agricultural, and surveying impacts of this coordinate change.
1. The 1.8 Meter Australian Plate Shift
The Australian tectonic plate is one of the fastest moving on Earth, shifting north-east at approximately 7 centimeters per year. By the year 2020, coordinates based on the legacy Geocentric Datum of Australia 1994 (GDA94) had drifted 1.8 meters from their absolute global positions tracked by satellites (WGS84/ITRF).
Warning: Raw GPS to CAD Coordinate Discrepancy
Combining uncorrected WGS84 drone data with NAD83 site plans creates a structural shift of 1-2 meters. Review the massive legal implications of this error.
Explore Boundary Dispute Liability2. Why GDA2020 Was Created
To align with modern GNSS (GPS) systems utilized by autonomous tractors, drones, and smartphones, the Australian government implemented GDA2020. This updated plate-fixed datum securely anchors local coordinates back in sync with global satellite readings for the year 2020.
3. Transformation: National Transformation Grids
To convert between GDA94 and GDA2020, Geoscience Australia provides two official grid transformation files (NTv2):
- Conformal Grid: Applies the 1.8m shift (7-parameter similarity).
- Conformal + Distortion Grid: Applies the 1.8m shift AND corrects localized distortions inherent in the aging GDA94 survey network.
誤った測地系（データム）の指定や、グリッド・地上補正（Grid-to-Ground）を適用しない座標変換は、1〜400mの位置ズレを引き起こします。これは測量過失請求や施工紛争の代表的な原因です。