Real Time Kinematics (RTK) is a technique used to enhance the precision of position data derived from satellite-based positioning systems. Traditional GPS measures the satellite code stream, which can only be measured to several meters. Additionally, traditional GPS loses precision as a result of ionospheres’ delay. The resulting position is only accurate to several meters. RTK provides centimetre-level position by using a different signal measurement and by correcting for ionospheres’ delay. Instead of measuring the code stream, an RTK receiver measures the carrier phase to under a centimetre. Next, RTK systems use two receivers, broadcasting corrections to each other to cancel out the ionospheres’ delay and output a relative position between the receivers.

RTK gives you centimetre-accurate relative positions between the two receivers. To get a position that is centimetre accurate with respect to the Earth, one unit must be used as a stationary base station. To get an absolute position (in a coordinate system such as ECEF), a CORS base station must be used or the base station must be placed at a known geodetic location. A list of these locations in the US can be found here. If both receivers are in motion, RTK will give you the relative position between the two but not fixed position relative to the environment.

A GPS satellite, orbiting at a nominal height of 26,440 km above Earth centre, completes a full orbit in 11 hours and 58 minutes. For an observer on the Earth's surface, nominally 6,300 km above Earth centre, a satellite transiting through zenith (directly above the observer) will take 5 hours and 3 minutes.

Like all GPS/GNSS receivers, the receiver must connect with at least four satellites. If these connections are lost, then the unit must reinitialize. Lost connection can occur due to dense vegetation coverage or buildings obstructing sky view (urban canyons).