GNSS data and product standards, originally developed to support collaboration within the IGS, have enjoyed widespread adoption worldwide.  They define the structure and content of coded ASCII and binary messages used to exchange satellite tracking data, precise orbit and clock states, and station coordinate solutions.  They also specify protocols for real-time and post-mission GNSS data interchange, enabling the combination of satellite tracking data acquired by different makes and models of receivers.  They also support the combination of coordinate solutions computed using different positioning software.

To date, the IGS has been the main source of open GNSS data and products for global scientific collaboration.  GNSS datasets archived at redundant global data centers are usually available in coded ASCII and binary formats.  Descriptions of IGS GNSS data and product formats can be found at the IGS website.  Table 4 summarizes the most common GNSS formats in use.

Table 4 Summary of IGS formats for GNSS data and products

Standard formats	Content
RINEX (Receiver-Independent Exchange format)	Multi-GNSS observations, GNSS broadcast navigation messages, Station meteorological data
IONEX (IONosphere Exchange format)	GNSS inter-frequency code biases and ionospheric TEC maps
ANTEX (ANTenna Exchange format)	Antenna phase center offsets, and variations wrt azimuth/elevation angle
SP3	Precise coordinates of GNSS satellites (center of mass estimates)
ERP	Earth rotation parameters (polar motion, length of day)
SINEX (Solution-INdependent EXchange format)	Station coordinates and velocity solutions and their covariance
TROPEX/ Troposphere SINEX	Tropospheric zenithal path delay

RINEX
The Receiver Independent Exchange (RINEX) format is used to encode different types of information such as: GNSS ranging measurements, GNSS broadcast navigation messages and surface meteorology.   Each RINEX file contains a header section with metadata followed by time stamped measurement records. A GNSS-specific compression/decompression algorithm (Hatanaka) is available to optimize the storage of RINEX files.  A variety of open software tools for conversion and validation of RINEX files are also made available by receiver manufacturers and research centers, for instance UNAVCO.

IGS also adopted RINEX-like formats to provide access to other GNSS products containing ionospheric maps, station tropospheric delays, antenna calibration values and precise satellite and station clock estimates.   The products are respectively called IONosphere-map EXchange (IONEX), ANTenna EXchange (ANTEX) and RINEX clock.  IONEX files contain global or regional maps of ionospheric Total Electron Content (TEC).  ANTEX files contain the 3D offset and azimuthal variations of the phase center of various calibrated GNSS antenna makes and models. The RINEX clock files contain the offsets of GNSS satellite and IGS receiver clocks with respect to the reference time used in a global network solution.

SP3
The precise orbit standard product version 3 (SP3) format contains precise GNSS satellite coordinates, clock offsets and associated accuracy codes. Four main SP3 versions have been developed to date (SP3-a (1989), SP3-b, (1998) SP3-c (2000), SPC3-d(2016)) to support the growing number of GNSS constellations.

SINEX
The Solution INdependent EXchange format supports the exchange and combination of station coordinates and related variance/covariance information resulting from geodetic network adjustments.  SINEX files are used mainly by geodetic agencies who integrate the coordinates and velocities of networks of continuously operating reference stations.  The SINEX format is central to the optimal combination of coordinates obtained from the global VLBI, SLR and GNSS networks used to maintain the International Terrestrial Reference Frame (ITRF).