Since its launch in 1973, the Global Positioning System (GPS) technology has evolved into a complete, comprehensive and practical field of study. Today, GPS technology is used in our mobile phones, computers, cars, defense equipment, mapping devices and software. GPS technology still has a long way to go. The future holds immense growth prospects for this amazing technology which definitely changed the course of human history. Since most of the common users don’t know the GPS-related technical terminology, we decided to write a GPS glossary for laymen, detailing the definition of the most important terms related to the GPS world.
GPS stands for Global Positioning System. This system uses real-time, 3-dimensional positioning to identify, calculate and show the direction, position and exact location of objects. GPS need global navigation satellite system (GNSS), geolocation and GPS receivers to work.
The process of identifying or generating coordinates of a specific object to find its location or direction is called geolocation. This information is used to infer meaningful data from the location of the objects.
Coordinates are numbers and symbols which represent the exact location of an object. Generally, the coordinate system uses three metrics: latitude, longitude and elevation.
Autonomous Positioning is the least precise, raw form of data which a GPS could produce. An AP generally has a chance of error within 10 meters.
A base station is a system which consist of a GPS antenna and a receiver, located at a special physical installation. It is used to collect base data and communicate it to a rover unit or a satellite.
Carrier Phase is the total difference between carrier signal generated by the internal oscillator of a roving receiver the signal emitted the GPS satellite.
CORS (Continuously Operating Reference) Station
It is a network or conglomerate of GPS base stations coordinated by the National Geodetic Survey that is used to provide GPS reference data to permit end users to perform post-processed differential correction of GPS data collected with roving receivers.
A data dictionary details the relationship between attributes produced by a GPS receiver.
Earth Centered, Earth Fixed (ECEF)
It is a complete coordinate system based on WGS-84 reference frame. The center of this system lies at the center of the Earth.
Latitude is a measurement which shows the north and south component of the coordinate system. This angular measurement, therefore, is taken fromthe center of the earth to north or south of the equator.
This angular measurement is taken from the center of the Earth to east or west of the Greenwich meridian (London, England).
Map projection is a method of transforming positions defined on an ellipsoid to a map grid.
It is a famous term in GPS which represents the Navigation Message broadcast by each GPS satellite on both the L1 and L2 transmitters. This message shows time, clock correction parameters, delay parameters, satellite vehicle’s ephemeris and other important metrics.
SBAS (Satellite Based Augmentation System)
SBAS refers to differential GPS applied to a big area, for example, a continent or a country.
VRS (Virtual Reference Station)
VRS provides corrections to rovers. It consist of GPS hardware equipment, communication links, channels and software. VRS sends information to rovers in the form of RTCM correction messages.
Carrie is a radio having at least one metric that could be identified using a referenced modulation operation. These metrics could be frequency, amplitude or phase.
Differential positioning (DGPS)
It is a technique used to rectify the positioning error at a location and then adding a correction factor.
Dithering is the process of introducing digital noise and disturbance in GPS signals to alter the results. Dithering is mostly used for defense purposes in order to disturb the enemy GPS systems.
Earth-centered earth-fixed (ECEF)
It is the Cartesian coordinate system in which the X direction is the intersection of the prime meridian (Greenwich) with the equator, while Z is the direction of the spin axis.
The P code or prediction code of a GPS signalis a pseudo-random binary biphase modulations on the GPS carrier at a chip rate of 10.23 MHz. This signal is repeated every 267 days.
World geodetic system
This is set of parameters showing the size of the Earth, positions of network of points with respect to the center of mass of the Earth, changes in major geodetic datums, and harmonic coefficients of earth.