Satellite navigation (satnav) or satellite positioning is the use of artificial satellites for navigation or geopositioning. A global navigation satellite system (GNSS) provides coverage for any user on Earth, including air, land, and sea. There are four operational GNSS systems: the United States Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), China's BeiDou Navigation Satellite System (BDS) and the European Union's Galileo. Furthermore, there are two regional navigation satellite systems (RNSS) in the form of Japan's Quasi-Zenith Satellite System (QZSS), and the Indian Regional Navigation Satellite System (IRNSS, also known as NavIC).
A satellite-based augmentation system (SBAS) is a system that is designed to enhance the accuracy of the global GNSS systems. The SBAS systems include Japan's Quasi-Zenith Satellite System (QZSS), India's GAGAN, and the European EGNOS, all of them based on GPS.
