Common GPS Terminology and Definitions



Benchmark Precisely surveyed points on the landscape, typically marked with a brass or metal disc in the ground. These can also be referred to as survey marks, control stations, or geodetic marks.
DGPSDifferential GPS (DGPS) is an enhancement to GPS which provides improved location accuracy through the use of a stationary receiver that is providing correction information to the receiver being used in the field (the rover receiver). The most common service is the submeter corrections supplied via the WAAS satellites over North America.
EGNOSThe European Geostationary Navigation Overlay Service (EGNOS) is Europe's satellite-based augmentation system (SBAS). It is used to improve the accuracy and performance of global navigational satellite constellations and was deployed to provide safety of life navigation services in terrestrial and maritime areas across much of Europe. Only available over Europe.
EllipsoidA mathematical model of the shape of the Earth which assumes the Earth is a perfect sphere, which it is not. Therefore, Ellipsoidal Height is not commonly used in reporting elevation values in mapping.
Ellipsoidal HeightHeight used to measure from an ellipsoidal surface to a point on the surface on the earth. Sometimes referred to as "raw elevation" before applying a Geoid model to determine Orthometric Height.
GAGANThe GPS Aided Geo Augmented Navigation (GAGAN) is a satellite-based augmentation system (SBAS) used over the Indian airspace. The system was developed to establish, deploy, and certify a SBAS system for safety-of-life aviation applications in India. Only available over India.
GalileoEuropean Union owned and operated navigational constellation. Available worldwide.
GeoidA surface model of the shape of the Earth based on gravity alone and defined by the federal government in the U.S. Differs from Mean Sea Level, which is affected by temperature, salinity, currents, wind, and more. Current Geoid model is Geoid12B with a new Geiod18 having been recently released.
GGAEssential fix data that supplies 3D location and accuracy data.
GLLGeographic Latitude and Longitude.
GLONASSRussian operated navigational satellite constellation. The second navigational constellation to be opened to the public.
GNSSGlobal Navigational Satellite System (GNSS). This is a more encompassing term for navigational satellites. A GNSS receiver is capable of utilizing at least two satellite constellations. Initially just GPS and Russian Glonass satellites. However, this term now includes the European Galileo and the Chinese Beidou and Japanese QZSS constellations.
GPSGlobal Positioning System (GPS). The American navigational satellite constellation is referred to as GPS. This constellation is comprised he baseline satellite constellation consists of 24 satellites positioned in six earth-centered orbital planes with four operation satellites and a spare satellite slot in each orbital plane. The system can support a constellation of up to thirty satellites in controlled and maintained by the US Air Force.
GSAProvides details related to the satellites being used for position fix
GSVRefers to the number of GPS Satellites in View (GSV). 
LatitudeLatitude is a north-south spherical directional coordinate system ranging from 0° (at the Equator) to 90° (at the north or south pole).
LongitudeLongitude is an east-west spherical directional coordinate system ranging from 0° to +180° (east) and -180° (west)
Map ProjectionA map projection is a systematic means of displaying a 3D ellipsoid or spheroid of the Earth to a 2D map surface.
MSASMTSAT Satellite Augmentation System (MSAS) is a Japanese SBAS systems developed with the goal of improving accuracy, integrity, and signal availability. The system uses a MTSAT system that is owned and operated by the Japanese Ministry of Land, Infrastructure and Transport. Available in the Pacific region surrounding Japan.
MTSATMultifunctional Transport Satellite (MTSAT) is a Japanese based dual-function satellite program developed to augment the air-traffic services through enhanced communication and positioning information and air traffic capabilities in the Asia-Pacific region. Additionally, the systems are a successor to the Geostationary Meteorological Satellite series (GMS), which is used for advanced meteorological observation capabilities, including data collection services.
North American Datum 1927 (NAD27)
NAD27 is the adjustment of long baseline surveys, which established a network of standardized horizontal positions on North America. This datum provides a frame of reference as a basis for placing specific points on the spheroid. NAD27 is one of three main geodetic datums used in North America. This datum uses Clarke Ellipsoid of 1866 with a fixed latitude and longitude of Meade's Ranch, Kansas (39°13’26.686? north latitude, 98°32’30.506? west longitude). Rarely used today.
North American Datum 1983 (NAD83)
NAD83 is a successor of NAD27. NAD83 creates a set of unified horizontal or geometric datum of North America. NAD83 corrects some of the distortions from NAD27 over distance by using sense set positions from terrestrial Doppler satellite data. NAD83 is geocentric datum offset by about 2meters. Currently used by most RTK networks and base stations around the U.S.
North American Vertical Datum of 1929 (NAVD29)
NAVD29 is a vertical datum that provides a reference surface heights (altitude) or depth (depression) above or below mean sea level (MSL). Mean sea level was held fixed at the sites of 26 tide gauges, 21 in the United States and 5 in Canada. he datum is defined by the observed heights of mean sea level at the 26 tide gauges and by the set of elevations of all bench marks resulting from the adjustment. Rarely used today.
North American Vertical Datum of 1988 (NAVD88)
NAVD88 is a vertical datum that provides a reference surface heights (altitude) or depth (depression) above or below mean sea level (MSL), which was established in 1991 by the minimum constraint adjustment of the Canadian-Mexican-United States level observations. NAVD88 consists of a leveling network on the North American Continent, ranging from Alaska, through Canada, across the United States, affixed to a single origin point on the continent. Currently used as the default elevation datum and referred to as Orthometric Height.
NMEANational Marine Electronics Association. A GPS receiver interprets satellite communications in the NMEA format. The most important NMEA sentences are GGA, GSA, GSV, RMC, GLL and VTG.
NTRIPNetwork Transport of RTCM via Internet Protocol. In other words, RTK streamed over the internet from a single base station or a network of base stations working collaboratively
Orthometric HeightOrthometric Height is a height measurement from the geoid surface to a point on the surface of the Earth. Currently Geoid12B is the default datum for Orthometric Height. However, a newer Geoid18 has been released but not commonly adopted.
PDOPPositional Dilution of Precision (PDOP) is a qualitative measurement system used to represent the quality of the satellite geometry when taking GPS readings.
Quasi-Zenith Satellite System
Known as QZSS, this is the Japanese navigational constellation. Only available around the Pacific region surrounding Japan.
RoverA Rover is a GPS/GNSS receiver that is being actively used to record the position of assets or features. It can be used as a standalone device with satellite corrections service (SBAS), or it can be used in conjunction with a Base Station for RTK workflows. In the case of RTK work, the Rover is wirelessly receiving real-time corrections from the nearby Base Station.
RTCMRadio Technical Commission for Maritime. International standards organization. RTK receivers can use data supplied in RTCM format.
RTKReal-Time Kinematic. RTK positioning is a differential GNSS method used by an RTK-enabled GNSS receiver to obtain precise positional corrections wirelessly when in the vicinity of an operational base station.
SBASSatellite-Based Augmentation System. This type of satellite provides a positional correction algorithm that a GPS or GNSS receiver can use to increase the accuracy of its position. The SBAS system for North America is WAAS.
SDCMSystem for Differential Correction and Monitoring (SDCM) is a SBAS system developed by the Russian Federation as a component of the GLONASS GNSS. The SDCM system is an SBAS argumentation system that is designed to perform integrity monitoring of both GPS and GLONASS satellites. The networks are comprised of ground segments, consisting of reference stations, central processing facilities, uplink stations and terrestrial broadcasting.
SpheroidA three-dimensional mathematical model representing the shape of the Earth based on equation of a sphere.
State Plane Coordinate System
State Plane Coordinate is a standardized system in the United States based on Lambert conformal conic and transverse Mercator projectors. There are more than 120 numbered sections, referred to as zones, covering the 50 United States, Puerto Rico, and the U.S. Virgin Islands. The systems were developed in the 1930s by the US Coast and Geodetic Survey to provide a common reference system to surveyors and mappers. It provides a conformal mapping system for the country with a maximum scale distortion of one part in 10,000.
UTMUniversal Transverse Mercator (UTM) is a standard set of map projections with a central meridian for each 6-degree wide UTM Zone.
VTGVector Track a Speed over Ground (VTG)
WAASWide-Area Augmentation System is the North American submeter SBAS system. There are three WAAS satellites that stay in geosynchronous orbit over North America and Hawaii. WAAS provides positional correction algorithms for the GPS constellation.
WGS84WGS84 is an Earth-centered and Earth-fixed terrestrial reference system and geodetic datum. It is based on a consistent set of constants and model parameters that describe the Earth's size, shape, and gravitational and geomagnetic fields. WGS84 is the standard of the US Department of Defense global reference system for geospatial information and is the referenced systems of the GPS system. WGS84 is also the basis for most online satellite imagery providers such as Google Earth and Maps, Apple Maps, Esri ArcGIS Online and Collector, and more.
VDOPVertical Dilution of Precision (VDOP) is a quantitative measurement, which is used to represent the quality of the GPS receiver's observed height, based on satellite geometry.