Official Transformation —HTDP / NADCON5
ΔX, ΔY, ΔZ = f(position, time)
For most CONUS practical work (sub-meter accuracy):
WGS84 ≁ENAD83(2011) + 1.0 to 2.0 m shift
EPSG transform: NAD83(2011) —ITRF2014 = EPSG:1188
Reference Table
| Region | NAD83→WGS84 Offset | Direction | Trend |
|---|---|---|---|
| CONUS (average) | 1— m | South/southwest | +1— cm/year |
| Hawaii | 3— m | Varies (Pacific plate) | +5— cm/year |
| Alaska | 1— m | North (different plate motion) | +2— cm/year |
| Puerto Rico | 0.5—.5 m | Southeast | +1— cm/year |
ngineering Consequences
For precision engineering, RTK drone surveys, and autonomous vehicle navigation, 1— meters is catastrophic. When a surveyor uses raw GNSS output (WGS84) to stake a building design drawn in NAD83(2011), the physical structure is placed 1— meters from the legal design position. This is a leading cause of:
- Boundary encroachment claims
- DOT contract non-compliance
- GPS-based construction staking disputes
Frequently Asked Questions
Does GPS output NAD83 or WGS84?
Raw GPS/GNSS receivers output coordinates in WGS84 (specifically tied to the current ITRF realization). To use these coordinates in a NAD83 engineering environment, you must apply a formal datum transformation via NGS NCAT or HTDP.
Is 1-2 meters a big deal?
For recreational use —no. For engineering, legal boundaries, and construction staking —absolutely yes. At a typical residential property line, 1 meter equals your entire setback buffer. In DOT highway work, 1 meter moves a structure from within the ROW to outside it.
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.