Navigation and positioning are primary applications of GNSS. Precise Point Positioning (PPP) enables autonomous user receiver positioning, thus without observations from nearby reference stations. Hence, the PPP can be used everywhere on the globe without a need of costly infrastructure.
A huge volume of GNSS observations is regularly collected for
various applications when disseminated via streams and files
for real-time and post-processing analysis, respectively.
Data from reference stations become more valuable when properly controlled and archived.
Due to the refractivity, the GNSS signal is bended and delayed when passing through the neutral atmosphere.
This non-dispersive effect reaches tens of meters depending on meteorological parameters along the signal path.
Hence, corrections must be applied in precise applications.