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Geopositioning
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Geopositioning is the process of determining or estimating the geographic position of an object or a person.[1] Geopositioning yields a set of geographic coordinates (such as latitude and longitude) in a given map datum. Geographic positions may also be expressed indirectly, as a distance in linear referencing or as a bearing and range from a known landmark. The resulting geoposition is sometimes referred to as geolocation, and the process of geopositioning may also be described as geo-localization. In turn, positions can be used to determine a more easily understandable location, such as a street address (see reverse geocoding).
Specific instances include:
- animal geotracking, the process of inferring the location of animals over time;
- positioning system, the mechanisms for the determination of geographic positions in general;
- internet geolocation, geolocating a device connected to the internet;
- and mobile phone tracking.[2]
Geofencing
[edit]Geofencing involves creating a virtual geographic boundary (a geofence), enabling software to trigger a response when a device enters or leaves a particular area.[3] Geopositioning is a pre-requisite for geofencing.
Background
[edit]Geopositioning uses various visual and electronic methods including position lines and position circles, celestial navigation, radio navigation, radio and WiFi positioning systems, and the use of satellite navigation systems.
The calculation requires measurements or observations of distances or angles to reference points whose positions are known. In 2D surveys, observations of three reference points are enough to compute a position in a two-dimensional plane. In practice, observations are subject to errors resulting from various physical and atmospheric factors that influence the measurement of distances and angles.[4]
A practical example of obtaining a position fix would be for a ship to take bearing measurements on three lighthouses positioned along the coast. These measurements could be made visually using a hand bearing compass, or in case of poor visibility, electronically using radar or radio direction finding. Since all physical observations are subject to errors, the resulting position fix is also subject to inaccuracy. Although in theory two lines of position (LOP) are enough to define a point, in practice 'crossing' more LOPs provides greater accuracy and confidence, especially if the lines cross at a good angle to each other. Three LOPs are considered the minimum for a practical navigational fix.[5] The three LOPs when drawn on the chart will in general form a triangle, known as a 'cocked hat'. The navigator will have more confidence in a position fix that is formed by a small cocked hat with angles close to those of an equilateral triangle. [6] The area of doubt surrounding a position fix is called an error ellipse. To minimize the error, electronic navigation systems generally use more than three reference points to compute a position fix to increase the data redundancy. As more redundant reference points are added, the position fix becomes more accurate and the area of the resulting error ellipse decreases.[7]
The process of using 3 reference points to calculate the location is called Trilateration, and when using more than 3 points, multilateration.
Combining multiple observations to compute a position fix is equivalent to solving a system of linear equations. Navigation systems use regression algorithms such as least squares in order to compute a position fix in 3D space. This is most commonly done by combining distance measurements to 4 or more GPS satellites, which orbit the Earth along known paths.[8]
The result of position fixing is called a position fix (PF), or simply a fix, a position derived from measuring in relation to external reference points. [9] In nautical navigation, the term is generally used with manual or visual techniques, such as the use of intersecting visual or radio position lines, rather than the use of more automated and accurate electronic methods like GPS; in aviation, use of electronic navigation aids is more common. A visual fix can be made by using any sighting device with a bearing indicator. Two or more objects of known position are sighted, and the bearings recorded. Bearing lines are then plotted on a chart through the locations of the sighted items. The intersection of these lines is the current position of the vessel.
Usually, a fix is where two or more position lines intersect at any given time. If three position lines can be obtained, the resulting "cocked hat", where the three lines do not intersect at the same point, but create a triangle, gives the navigator an indication of the accuracy. The most accurate fixes occur when the position lines are perpendicular to each other. Fixes are a necessary aspect of navigation by dead reckoning, which relies on estimates of speed and course. The fix confirms the actual position during a journey. A fix can introduce inaccuracies if the reference point is not correctly identified or is inaccurately measured.
Indoor geopositioning
[edit]Geopositioning can be referred to both global positioning and outdoor positioning, using for example GPS, and to indoor positioning, for all the situations where satellite GPS is not a viable option and the localization process has to happen indoors. For indoor positioning, tracking and localization there are many technologies that can be used, depending on the specific needs and on the environmental characteristics.[10]
See also
[edit]- Attitude determination
- Direction determination
- Dynamic positioning
- Geo-blocking
- Geocoding
- Geodetic positioning
- GPS tracking unit
- Geotagging
- Geotargeting
- Indoor positioning
- Latitude determination
- Longitude determination
- Location-based service
- Satellite navigation software
- Triangulation
- Vertical position measurement
- W3C Geolocation API
References
[edit]- ^ "geopositioning". ISO/TC 211 Geolexica. 2020-06-02. Retrieved 2020-08-31.
- ^ Keating, J.B.; United States. Bureau of Land Management (1993). The Geo-Positioning Selection Guide for Resource Management. BLM technical note. Bureau of Land Management. p. 5. Retrieved 2020-08-31.
- ^ "What is geofencing and how is it used? – TechTarget Definition". WhatIs. Retrieved 2024-09-10.
- ^ B. Hofmann-Wellenhof; K. Legat; M. Wieser (28 June 2011). Navigation: Principles of Positioning and Guidance. Springer Science & Business Media. ISBN 978-3-7091-6078-7.
- ^ Gentile, C.; Alsindi, N.; Raulefs, R.; Teolis, C. (2012). Geolocation Techniques: Principles and Applications. Springer New York. ISBN 978-1-4614-1836-8. Retrieved 2020-08-31.
- ^ Progri, I. (2011). Geolocation of RF Signals: Principles and Simulations. Springer New York. ISBN 978-1-4419-7952-0. Retrieved 2020-08-31.
- ^ Nait-Sidi-Moh, A.; Bakhouya, M.; Gaber, J.; Wack, M. (2013). Geopositioning and Mobility. ISTE. Wiley. p. 71. ISBN 978-1-118-74368-3. Retrieved 2020-08-31.
- ^ Laurie Tetley; David Calcutt (7 June 2007). Electronic Navigation Systems. Routledge. pp. 9–. ISBN 978-1-136-40725-3.
- ^ Zamir, A.R.; Hakeem, A.; Van Gool, L.; Shah, M.; Szeliski, R. (2016). Large-Scale Visual Geo-Localization. Advances in Computer Vision and Pattern Recognition (in Romanian). Springer International Publishing. ISBN 978-3-319-25781-5. Retrieved 2020-08-31.
- ^ Brena, Ramon F.; García-Vázquez, Juan Pablo; Galván-Tejada, Carlos E.; Muñoz-Rodriguez, David; Vargas-Rosales, Cesar; Fangmeyer, James (2017). "Evolution of Indoor Positioning Technologies: A Survey". Journal of Sensors. 2017: 1–21. doi:10.1155/2017/2630413. hdl:11285/630311. ISSN 1687-725X.
Further reading
[edit]- Zekavat, R.; Buehrer, R.M. (2019). Handbook of Position Location: Theory, Practice, and Advances. IEEE Series on Digital & Mobile Communication. Wiley. ISBN 978-1-119-43460-3. Retrieved 2021-02-19.[permanent dead link]
- Munoz, D.; Lara, F.B.; Vargas, C.; Enriquez-Caldera, R. (2009). Position Location Techniques and Applications. Elsevier Science. ISBN 978-0-08-092193-8. Retrieved 2021-02-19.
External links
[edit]
Media related to Geolocation at Wikimedia Commons
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Geopositioning
View on Grokipediafrom Grokipedia
Geopositioning is the process of determining an object's location, typically in navigation contexts, by identifying its geographic coordinates such as latitude and longitude relative to Earth's surface.[1] This technique yields precise positional data, often including height, enabling applications from basic mapping to advanced tracking.[2]
Geopositioning employs various methods, with global navigation satellite systems (GNSS) serving as the primary approach for outdoor, worldwide applications. The Global Positioning System (GPS), operated by the United States, is a key GNSS providing positioning, navigation, and timing (PNT) services.[3] Other GNSS include Russia's GLONASS, Europe's Galileo, and China's BeiDou. These systems use trilateration, where receivers calculate position by measuring signal travel times from multiple satellites, achieving civilian accuracies typically within a few meters.[4] Augmentation techniques, such as Differential GPS (DGPS), enhance precision further.[5]
Additional methods include terrestrial systems (e.g., radio beacons), network-based approaches (e.g., cellular triangulation), and indoor/sensor-based technologies (e.g., Wi-Fi or inertial navigation). Geopositioning supports diverse applications, including navigation in transportation, location-based services, asset tracking, precision agriculture, emergency response, and synchronizing critical infrastructure like telecommunications and financial networks.[6][7]
where is the speed of light, is the signal reception time at the receiver, is the transmission time from the satellite, and encompasses errors such as clock biases, ionospheric and tropospheric delays, multipath effects, and receiver noise.[44] This measurement, combined with satellite ephemeris data, enables trilateration for 3D positioning after accounting for receiver clock offset.[45] GNSS signals are structured as spread-spectrum transmissions in the L-band to ensure robustness against interference, featuring pseudorandom noise (PRN) codes modulated onto carrier waves. The coarse/acquisition (C/A) code, a 1,023-bit Gold code repeating every millisecond on the L1 frequency (1,575.42 MHz), supports civilian access with meter-level accuracy by allowing code correlation for timing. For higher precision, carrier phase measurements track the phase of the unmodulated carrier signal on multiple bands—L1, L2 (1,227.60 MHz), and L5 (1,176.45 MHz)—enabling centimeter-level positioning through ambiguity resolution, while dual- or triple-frequency operation mitigates atmospheric errors.[46] Integrating multiple GNSS constellations, such as the U.S. GPS and European Galileo, significantly boosts performance by expanding the pool of visible satellites—often over 30 in combined view versus 8–12 from a single system—enhancing availability, redundancy, and accuracy in urban or forested areas.[47] Complementary augmentation systems further refine accuracy: the Wide Area Augmentation System (WAAS) in North America and the European Geostationary Navigation Overlay Service (EGNOS) in Europe broadcast differential corrections for satellite orbits, clocks, and ionospheric delays via geostationary satellites, reducing errors to sub-meter levels while providing integrity alerts for aviation safety.[48][49] By 2025, GNSS capabilities have advanced with the ongoing rollout of next-generation satellites, including the GPS III series, which has increased the operational constellation to over 30 active vehicles for improved global coverage and signal strength. These satellites incorporate enhanced anti-jamming features, such as regional military (M-code) signals with higher power and directional antennas, offering up to eight times the jamming resistance of legacy systems to counter interference threats. The ninth GPS III satellite (SV-09) was declared launch-ready by late 2025, further bolstering resilience and precision.[50][51]
Fundamentals
Definition and Principles
Geopositioning is the process of determining or estimating the geographic location of an object, device, or person on Earth's surface through the analysis of signals and data from various sources.[8] This determination typically yields a position in three dimensions, incorporating latitude (north-south position), longitude (east-west position), and altitude (height above a reference surface such as sea level).[9] These coordinates form the basis for position fixing, where distances to known reference points are calculated using time-of-flight measurements of signals, enabling the intersection of geometric loci to pinpoint the location. A fundamental distinction in geopositioning lies between absolute and relative approaches. Absolute positioning establishes a location directly with respect to a global reference frame, such as the Earth's center or surface, often resulting in standalone coordinates with meter-level accuracy depending on the method.[10] In contrast, relative positioning computes the location in relation to one or more fixed reference points, which can enhance precision by mitigating common errors like atmospheric delays; for instance, a smartphone might fix its position by triangulating signals from multiple nearby cell towers or beacons as reference points.[10] Global Navigation Satellite Systems (GNSS) serve as a primary enabler for both modes by providing widespread signal coverage.[9] For applications requiring sub-meter accuracy, real-time kinematic (RTK) positioning represents a key advancement in relative geopositioning techniques. RTK employs differential corrections transmitted in real time from a fixed base station at a known location to a mobile receiver, compensating for shared errors in signal propagation and satellite clock inaccuracies.[11] The method relies on precise carrier-phase tracking of GNSS signals, where integer ambiguities in phase measurements are resolved to achieve centimeter-level precision over baselines up to tens of kilometers, making it essential for surveying and precision agriculture.[12]Coordinate Systems
Geographic coordinate systems (GCS) provide a framework for representing positions on Earth's surface using angular measurements of latitude and longitude, typically referenced to an ellipsoidal model of the planet. Latitude measures the angle north or south of the equator, ranging from 0° at the equator to 90° at the poles, while longitude indicates the angle east or west of the prime meridian, spanning from 0° to 180°. These coordinates are defined on a reference ellipsoid, which approximates Earth's shape as an oblate spheroid to account for its equatorial bulge and polar flattening. The World Geodetic System 1984 (WGS 84) serves as the global standard for GCS in geopositioning, utilizing a semi-major axis of 6,378,137 meters and a flattening factor of 1/298.257223563.[13] In three-dimensional applications, WGS 84 incorporates ellipsoidal height above the ellipsoid surface, enabling precise positioning in latitude (φ), longitude (λ), and height (h) format.[14] This system underpins global navigation satellite systems by providing a consistent reference for computing positions from satellite signals.[15] Projected coordinate systems transform the curved surface of the Earth onto a flat plane for mapping and analysis, addressing the inherent distortions of such projections through zone-based designs. The Universal Transverse Mercator (UTM) system exemplifies this approach, dividing the world into 60 longitudinal zones, each 6° wide and extending from 80°S to 84°N latitude, to minimize scale distortions within each zone.[16] UTM employs a transverse Mercator projection, where the cylinder of projection is tangent along the central meridian of each zone, resulting in near-zero scale distortion along that meridian and controlled east-west distortion that increases toward zone edges, typically limited to 0.1% within 1,000 km.[17] Coordinates in UTM are expressed in meters as easting (x) and northing (y), with a false easting of 500,000 m at the central meridian to avoid negative values, facilitating accurate distance and area calculations on maps.[18] Datum transformations are essential for reconciling positions across different reference frames, as geodetic datums like NAD83 and WGS 84, while closely aligned, exhibit small offsets due to variations in ellipsoid definitions and realization epochs. NAD83, primarily used in North America, is based on the GRS 80 ellipsoid with a semi-major axis of 6,378,137 m and flattening of 1/298.257222101, differing slightly from WGS 84 in its gravitational model and continental focus.[19] For such datums, transformations often use a simplified three-parameter geocentric translation rather than the full seven-parameter Helmert similarity transformation, which accounts for translations (ΔX, ΔY, ΔZ), rotations (R_x, R_y, R_z), and scale (s). The Helmert formula is given by: where rotations are in radians and scale in parts per million (ppm).[20] For NAD83 (HARN) to WGS 84, an approximate three-parameter geocentric translation uses ΔX = -0.991 m, ΔY = 0.025 m, ΔZ = 0.110 m, yielding sub-meter accuracy for most applications.[21] Vertical datums establish the reference for heights, distinguishing between ellipsoidal heights from GCS and orthometric heights relative to Earth's gravity field. Mean sea level (MSL), defined as the average height of the ocean surface over a 19-year tidal cycle, traditionally serves as the zero reference for many national vertical datums, such as the North American Vertical Datum of 1988 (NAVD 88) in the United States.[22] However, MSL varies locally due to gravitational anomalies and ocean dynamics, necessitating geoid models to relate ellipsoidal heights to orthometric heights. The geoid represents an equipotential surface approximating global MSL extended under continents, modeled by organizations like NOAA through gravity measurements and satellite altimetry.[23] Tools like NOAA's VDatum facilitate transformations between ellipsoidal, tidal, and orthometric datums, incorporating geoid undulations (N) via the relation h = H + N, where h is ellipsoidal height and H is orthometric height, to ensure consistent altitude determination in geopositioning.[24]Historical Development
Pre-Satellite Era
Geopositioning in the pre-satellite era relied on manual techniques and emerging radio-based systems to determine location without orbital assistance. Ancient mariners employed dead reckoning, estimating position from a known starting point by integrating speed, time, and direction of travel, though this method accumulated errors from unaccounted factors like currents and winds.[25] Celestial navigation supplemented dead reckoning by using observations of celestial bodies such as stars, the sun, and the moon relative to the horizon to compute latitude and longitude.[25] Instruments like the sextant, developed in the early 18th century, measured angular distances between these bodies and the horizon, while accurate timekeeping was essential for longitude calculations; John Harrison's H4 marine chronometer, completed around 1759 and tested successfully in 1761–1764 voyages to Jamaica and Barbados, achieved the precision needed to solve the longitude problem at sea, losing only seconds over months-long journeys.[26] In the 20th century, radio navigation systems introduced electronic aids for more reliable positioning, particularly during wartime. The Long Range Navigation (LORAN) system, developed at MIT's Radiation Laboratory starting in 1942 and operational by early 1943, used hyperbolic positioning by measuring time differences in pulsed radio signals from synchronized pairs of ground stations.[27] These stations formed chains, such as the North Atlantic chain with sites in the U.S., Canada, Greenland, Iceland, and the UK by 1944, enabling coverage over 60 million square miles and supporting Allied convoys, aircraft, and ships without breaking radio silence during World War II.[27] Similarly, the Decca Navigator, conceived in 1937 and trialed in 1942 under UK Admiralty auspices, employed continuous-wave phase comparison at harmonically related low frequencies (around 70–130 kHz) for hyperbolic positioning, providing accuracy within hundreds of meters over ranges up to 200 miles.[28] Deployed for Operation Neptune on D-Day in 1944, it guided minesweepers and landing craft through English Channel minefields using a chain of stations near Chichester, Swanage, and Beachy Head.[28] During the Cold War, the Omega system extended global reach with very low frequency (VLF) signals at 10–14 kHz, proposed in 1947 by J.A. Pierce and evolving from experimental setups to a network of eight stations by the mid-1970s, including sites in the U.S., Norway, Australia, and Japan.[29] Operating on phase difference principles with atomic clock synchronization, Omega provided all-weather worldwide coverage for aviation, maritime, and land use, with conventional accuracy of 1–2 nautical miles.[29] These systems marked a shift from manual to automated geopositioning but faced inherent challenges that limited their precision and reliability. LORAN signals, transmitted in the 1.7–1.9 MHz band, suffered from skywave interference at night due to ionospheric reflections, reducing daytime ground-wave accuracy from 0.25 nautical miles to several miles, while requiring line-of-sight or near-ground propagation for optimal performance.[27][30] Decca's lower frequencies mitigated some propagation issues but were vulnerable to atmospheric disturbances like thunderstorms, causing signal fading, and its shorter range—about half that of LORAN—necessitated denser station networks.[28][31] Omega, while globally extensive, required correction tables for ionospheric variations affecting VLF propagation, and its broad lane widths demanded additional aids to resolve ambiguities.[29] These constraints, including vulnerability to natural and man-made interference, underscored the need for more robust technologies in later developments.Satellite Navigation Systems
The development of the TRANSIT system by the U.S. Navy in the 1960s pioneered operational satellite navigation. Conceived in the late 1950s at the Johns Hopkins University Applied Physics Laboratory, TRANSIT utilized Doppler shift measurements from satellites in low-Earth orbit to enable position fixes, primarily for naval applications like submarine navigation. The first TRANSIT satellite launched in 1960, and the system achieved full operational status in 1964 with a constellation of up to five satellites plus spares, providing global coverage through polar orbits at approximately 1,100 km altitude.[32][33] The Global Positioning System (GPS), deployed by the United States, advanced satellite navigation to a medium-Earth orbit architecture for continuous global service. Development began in the 1970s, with the first experimental Block I satellite launched in 1978 using Atlas launch vehicles; these prototypes tested key technologies before transitioning to the operational Block II series in 1989. GPS reached full operational capability on April 27, 1995, with a nominal constellation of 24 Block II/IIA satellites orbiting at about 20,200 km. To protect military advantages, the U.S. implemented Selective Availability, which intentionally degraded civilian signal accuracy until its discontinuation by executive order on May 2, 2000, thereby granting public users access to near-military precision.[34][35] Parallel efforts by other nations established independent systems, fostering a multi-constellation era. The Soviet Union's GLONASS program launched its inaugural satellite in October 1982 as a counter to GPS, evolving into a 24-satellite constellation distributed across three orbital planes at 19,100 km altitude to deliver global positioning, navigation, and timing services; full operational deployment occurred by 1995. Europe's Galileo, under the European Union and European Space Agency, initiated open services in December 2016 with an initial set of satellites, building toward a full 24- to 30-satellite constellation in medium-Earth orbit for civilian-focused high-accuracy applications. China's BeiDou Navigation Satellite System achieved global coverage in June 2020, completing a core 24-satellite medium-Earth orbit segment supplemented by geostationary and inclined geosynchronous satellites, enabling worldwide services from its origins in regional Asian-Pacific operations since 2000.[36][37][38] Ongoing advancements have enhanced these systems' performance and interoperability. GPS modernization in the 2010s introduced the L5 civil signal on Block IIF satellites, with the first such launch in May 2010, providing dual-frequency capabilities for better interference resistance and accuracy in aviation and other sectors. By 2025, multi-constellation receivers integrating signals from GPS, GLONASS, Galileo, and BeiDou predominate in commercial and professional applications, offering improved availability and redundancy through combined observations from over 100 satellites worldwide.[39][40]Core Technologies
Global Navigation Satellite Systems
Global Navigation Satellite Systems (GNSS) form the backbone of satellite-based geopositioning, providing global coverage through a coordinated architecture of orbiting satellites, ground infrastructure, and user equipment. The system comprises three primary segments: the space segment, which consists of a constellation of satellites in medium Earth orbit transmitting positioning signals; the control segment, made up of a network of ground monitoring stations and control centers that track satellite health, upload corrections, and maintain orbital accuracy; and the user segment, encompassing receivers in devices like smartphones and vehicles that acquire and process these signals to compute position, velocity, and time.[41][42][43] Position determination relies on pseudorange measurements, which estimate the distance from the receiver to each satellite based on signal propagation time. The pseudorange is mathematically expressed aswhere is the speed of light, is the signal reception time at the receiver, is the transmission time from the satellite, and encompasses errors such as clock biases, ionospheric and tropospheric delays, multipath effects, and receiver noise.[44] This measurement, combined with satellite ephemeris data, enables trilateration for 3D positioning after accounting for receiver clock offset.[45] GNSS signals are structured as spread-spectrum transmissions in the L-band to ensure robustness against interference, featuring pseudorandom noise (PRN) codes modulated onto carrier waves. The coarse/acquisition (C/A) code, a 1,023-bit Gold code repeating every millisecond on the L1 frequency (1,575.42 MHz), supports civilian access with meter-level accuracy by allowing code correlation for timing. For higher precision, carrier phase measurements track the phase of the unmodulated carrier signal on multiple bands—L1, L2 (1,227.60 MHz), and L5 (1,176.45 MHz)—enabling centimeter-level positioning through ambiguity resolution, while dual- or triple-frequency operation mitigates atmospheric errors.[46] Integrating multiple GNSS constellations, such as the U.S. GPS and European Galileo, significantly boosts performance by expanding the pool of visible satellites—often over 30 in combined view versus 8–12 from a single system—enhancing availability, redundancy, and accuracy in urban or forested areas.[47] Complementary augmentation systems further refine accuracy: the Wide Area Augmentation System (WAAS) in North America and the European Geostationary Navigation Overlay Service (EGNOS) in Europe broadcast differential corrections for satellite orbits, clocks, and ionospheric delays via geostationary satellites, reducing errors to sub-meter levels while providing integrity alerts for aviation safety.[48][49] By 2025, GNSS capabilities have advanced with the ongoing rollout of next-generation satellites, including the GPS III series, which has increased the operational constellation to over 30 active vehicles for improved global coverage and signal strength. These satellites incorporate enhanced anti-jamming features, such as regional military (M-code) signals with higher power and directional antennas, offering up to eight times the jamming resistance of legacy systems to counter interference threats. The ninth GPS III satellite (SV-09) was declared launch-ready by late 2025, further bolstering resilience and precision.[50][51]