GPS receivers measure a signal’s “time of flight” as discussed earlier. The atmosphere around the earth is constantly changing and variations cause time of flight errors (signals can randomly slow down and thus add errors to the position calculation).

RTK (Real Time Kinematics); a fixed base station communicates with a roving GPS Receiver to remove sources of error. RTK performance depends on the survey accuracy of the fixed base antenna, quality of sky view at base location and distance between base and rover (known as baseline, the shorter the baseline distance, the better the accuracy). Generally, you want to be within 10 miles of the RTK base station.

You may hear the term “VRS RTK”. VRS (Virtual Reference Station) uses advanced mathematical models to provide high-accuracy GPS location data by generating a virtual reference station, rather than relying on a single, fixed RTK base station. In a VRS system, multiple RTK reference stations (often 10 or more) are networked together. The VRS model estimates, based on your location within the network, what the correction data from a nearby base station would be, using the error signals from all the reference stations. This allows for greater flexibility in positioning, as the user can move freely within the coverage area without needing to switch base stations or service providers.

VRS accuracy is generally slightly lower (~10cm or 4”) than a fixed solution that is very close to a base station, but VRS has the ability of being more flexible regarding travel distance and is often a less expensive service due to the reduced infrastructure required.

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