Farmers who use a local RTK network or state-run Real Time Network (RTN) — Iowa and Ohio both offer these signals — for auto steer and GPS guidance systems will need to recapture new GPS coordinates for field boundaries and A-B lines before spring planting.
That’s because The National Geodetic Survey (NGS) will soon replace two outdated reference frames, NAD 83 and NAVD 88, with a new corrections datum. The shift could knock your current A-B lines and GPS field boundaries off by anywhere from 1 to 4 meters, according to a pair of Iowa State University Extension precision ag specialists.
The Ohio State University Extension and FABE professor Dr. John Fulton issued a similar warning last fall at the Ohio Farm Science Review.
Iowa State University precision ag engineer Luke Fuhrer and digital Extension specialist Doug Houser say farmers using a major commercial satellite RTK network, such as those offered by John Deere and Trimble, should be OK for 2026.
Farmers who need to make quick updates to field boundaries or A-B lines, or check on the potential impact to existing telematics data this winter, are being told to use the free NGS Coordinate Conversion and Transformation Tool (NCAT) to shift their GPS coordinates from NAD 83/NAVD 88 to NATRF2022.
Fuhrer and Houser also want you to consider:
- Physically recollecting GPS coordinates for field boundaries, control points or benchmarks using a system aligned to the new datum.
- Recalculating your historical data using updated reference points or transformation software.
Example Scenario
The Iowa State researchers share the following scenario as an example of a farmer who will need to make updates before spring planting:
“A farmer in eastern Iowa has been using a local RTK base station tied to NAD 83 to map field boundaries with sub-inch accuracy to avoid a neighbor’s fence line.
“After 2026, the new NATRF2022 datum will shift those GPS-defined boundaries by several feet. While the fence hasn’t moved, the guidance lines will now show up partially in the neighbor’s field. Without correction, auto-steer will drift across actual property lines.”
Before spring 2026, Fuhrer and Houser want this farmer to:
- Back up all current GPS files and data.
- Talk to his/her equipment dealer about firmware updates or new coordinate system support.
- Use NCAT or dealer-provided tools to test a few key points and see how much they move.
- Consider a quick resurvey for high-value areas.
For more info, check out the NGS “Get Prepared” resource here.
