How Distance Impacts NTRIP RTK Accuracy and How Network RTK Helps

RTK accuracy gets worse as the rover moves away from its reference station, because the errors that the base and rover share stop matching over longer distances. Receiver makers express this as a fixed error plus a distance term in parts per million (ppm), where 1 ppm adds 1 mm of error per kilometer. This guide explains how NTRIP RTK accuracy changes with distance, how far you can work from a single base, and how network RTK and a nearby base reduce the effect.

Overview and context

RTK (real-time kinematic) positioning is used wherever positions must be accurate to a few centimeters, from surveying and construction to autonomous vehicles. It uses a base station at a known position and a moving rover. Both track the same satellites, and the base sends corrections so the rover can cancel the errors they share. NTRIP delivers those corrections over the internet instead of a radio link, as our guide to what NTRIP is explains. Our NTRIP connection flow guide covers the protocol itself.

Internet delivery removes the radio range limit, but not the physics. Satellite geometry, the atmosphere, reflected signals and blockages also affect the result. Our accuracy guidance names the distance to the nearest base station as the primary factor. For what centimeter-level accuracy means in the field, see our guide to RTK GPS accuracy.

Why RTK accuracy decreases with distance

The base and rover can only cancel errors they both experience, because the corrections describe conditions at the base. NGS's single-base guidelines explain that atmospheric delays cancel as long as baselines are kept relatively short, 20 km or less, so that conditions do not differ between base and rover. As the distance grows, ionospheric delay and satellite orbit errors decorrelate, and most manufacturers add about 1 ppm to account for them.

Vertical accuracy degrades first. NGS notes that tropospheric error mainly affects height, which is one reason vertical specifications are roughly double the horizontal ones.

The receiver matters too. According to NGS, newer receivers with better RTK algorithms produce better accuracy over longer baselines. So what is the range of single-base RTK? Navipedia describes RTK as usable up to 10 or 20 km from the base, and NGS recommends 20 km or less for survey work. Beyond that, accuracy keeps degrading as the ppm term grows. With RTKdata, aim to work within 15 km of a base station for the best results.

Network RTK and NTRIP: minimizing the distance effect

A real-time network (RTN) combines many reference stations. NGS names the main accuracy benefit: the first-order ppm error is eliminated or drastically reduced, because ionospheric, tropospheric and orbital errors are interpolated to the rover's site. The network also removes the need for your own base station.

Station spacing still matters. The Trimble R12i specification for network RTK is 8 mm + 0.5 ppm horizontal and 15 mm + 0.5 ppm vertical, and Trimble notes that the network ppm is referenced to the closest physical base station.

RTKdata's AUTO mountpoint uses the GGA position your receiver sends to select the nearest base station, as our connection reference explains. The distance that matters is the distance to that base, so check your site on the coverage map, where the 2 cm zone marks survey-grade RTK. Our guide to reading a GNSS corrections map explains the zones.

Why choose RTKdata.com for reliable NTRIP RTK

With a correction service, you don't need to set up and maintain your own base station. RTKdata delivers NTRIP corrections to GNSS receivers, field software, machine guidance and drones, including the DJI Matrice 350 RTK. Where there is no base nearby, you can host an RTKdata base station or run your own, and our base-station guide compares the options.

You can test coverage and accuracy at your own site with the 30-day free trial, or book a meeting for multi-rover and enterprise projects.

RTK vs. other systems

• Standalone GPS: GPS.gov says GPS-enabled smartphones are typically accurate to within a 4.9 m radius under open sky.
• Code-based differential GNSS (DGPS): Trimble specifies 0.25 m + 1 ppm horizontal for the R12i, and Navipedia puts classic DGPS at about 1 m.
• RTK: centimeter level near the base, plus the distance term described above.

How to keep RTK accuracy over distance

1. Work close to a base station. Check the distance on the coverage map first, so you know which accuracy zone your site is in.
2. Keep a clear view of the sky. Our accuracy guidance rates open ground with nothing above 15 degrees elevation as best.
3. Avoid reflective surfaces. The same guidance also calls multipath the biggest cause of lost accuracy after distance. Our multipath guide explains how to work around it.
4. Keep correction latency low. Our guidance gives full RTK performance below 1 second of latency, so use a stable mobile data connection.
5. Use a multi-frequency receiver. NGS notes that dual-frequency combinations give the most accurate solutions on extended baselines, so they help most when the base is farther away.
6. Check against known points. A fixed solution is not proof of accuracy, so measure a known point before collecting data.