The BaselineThe distance between the base station and your rover. Shorter is better for accuracy.More is the distance between the Base stationA GNSS receiver sitting still on a known spot. It figures out how wrong the satellite signals are right now and shares that as corrections.More and your RoverThe receiver that moves around the job, like a survey pole or a drone. It uses the base's corrections to find its exact spot.More. The longer it is, the less accurate you get.
Receiver spec sheets show RTKReal-time kinematic. A way to make GPS accurate to about an inch by getting live corrections from a nearby base station.More accuracy in two parts, like "8 mm + 1 ppm". The first part is a fixed amount of error. The second part grows with distance. ppm means parts per million. 1 ppm works out to 1 millimeter of extra error for every kilometer of baseline.
NGSNational Geodetic Survey. The part of NOAA that runs the official US coordinate system, CORS and OPUS.More's guidelines explain why. Over a short distance, the base and rover see almost the same air, the same satellite OrbitsThe paths satellites follow. Precise orbit files tell software exactly where each satellite was.More and the same delays. Spread them apart and those things start to differ. NGS recommends keeping single-base distances short, at 20 km (about 12 miles) or less.
- At 10 km, 1 ppm adds 10 mm (about 0.4 inch). At 40 km it adds 40 mm, and getting a fix also takes longer and fails more often.
- A network using VRSVirtual reference station. The network blends nearby stations to create a pretend base right next to you, which keeps the baseline short.More blends data from many stations to model the error. So the distance to the nearest real station matters less than it does with one base. How close together the stations are still makes a difference.
- Height (vertical) error is usually bigger than side-to-side (horizontal) error. Spec sheets normally list both.
Check your distance: the Nearest base station tool uses your location to find the closest NOAANational Oceanic and Atmospheric Administration. The US agency that includes NGS and runs the CORS network.More CORSContinuously Operating Reference Station. A permanent GPS receiver that records satellite data all day, every day.More station.