The “accuracy in real-time“ problem
Global Navigation Satellite Systems (GNSS) like GPS, Galileo and others enable positioning by determining the range between a satellite and an observer.
The apparent range (pseudo range) results from the observed travelling time of a signal transmitted from a satellite to a receiver multiplied by the speed of light. The travelling time is affected by several error sources, including satellite orbit and clock errors, biases of the satellite and receiver hardware as well as ionospheric and tropospheric effects.
These effects lead to inaccuracies in real-time positioning of about 3 to 8 meters when using the satellite signals only.
GNSS augmentation service providers generate GNSS corrections by continuously monitoring the signals received by reference stations. With such GNSS real-time correction services, the inaccuracies are reduced down to centimeter or even millimeter level.