📐 Official Transformation — Geocentric NTv2 Grid
Method 1 (Conformal only):
X_GDA2020 = X_GDA94 + ΔX (from Helmert)
Shift ≈ 1.8 m NE in most of Australia
Method 2 (Conformal + Distortion — recommended):
Applies 1.8m + localized distortion corrections
EPSG: GDA94 → GDA2020 = EPSG:8447 (NTv2 grid method)
📊 Reference Table
| Location | Approx. Shift (metres) | Primary Direction | Note |
|---|---|---|---|
| Sydney, NSW | 1.80 m | North-northeast | Matches national average |
| Melbourne, VIC | 1.79 m | North-northeast | Matches national average |
| Perth, WA | 1.82 m | North-northeast | Fastest-moving region |
| Darwin, NT | 1.78 m | North-northeast | Slightly different orientation |
| Hobart, TAS | 1.78 m | North-northeast | Southern extent slowest |
⚠️ Engineering Consequences
Mixing GDA94 and GDA2020 spatial datasets without transformation causes systematic 1.8 m misplacement across all mapped features. In practice this means:
- Cadastral parcel boundaries appear 1.8 m from their actual position
- Infrastructure (pipelines, roads, utilities) registered in GDA94 will not align with new GDA2020 surveys
- Modern autonomous agriculture equipment operating from GDA2020 GPS will have systematic errors relative to GDA94 farm plans
- Regulatory non-compliance for projects submitted to agencies requiring GDA2020 since it became mandatory
Frequently Asked Questions
Is GDA2020 now mandatory in Australia?
Yes. Most Australian state jurisdictions have mandated GDA2020 for new cadastral surveys and government spatial data submissions. NSW and WA both have transitional policies requiring data providers to migrate and flag the datum used.
Do I always need the full NTv2 grid transformation?
For most professional survey work — yes. The conformal-plus-distortion NTv2 grid is the recommended method. A simple 7-parameter Helmert captures the bulk 1.8 m shift but misses localized network distortions inherited from the GDA94 adjustment, which matter at the cm level.
Using the wrong datum or applying coordinates without grid-to-ground correction can cause 1–400 metre positional errors — a leading cause of surveying negligence claims and contract disputes.