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Geopositioning
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<h2 id="geofencing">Geofencing</h2> <p><i>Geofencing</i> involves creating a virtual geographic boundary (a <a href="/facts/Geofence/p9R1RuSJ">geofence</a>), enabling software to trigger a response when a device enters or leaves a particular area.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> Geopositioning is a pre-requisite for geofencing. </p> <h2 id="background">Background</h2> <p>Geopositioning uses various visual and <a href="/facts/Electronics/E4JhgISq">electronic</a> methods including <a href="/facts/Position_line/KVdYVLCc">position lines</a> and <a href="/facts/Position_circle/dlPtj8BN">position circles</a>, <a href="/facts/Celestial_navigation/pCpbhzJt">celestial navigation</a>, <a href="/facts/Radio_navigation/sRkrEaG9">radio navigation</a>, <a href="/facts/Wi-Fi_positioning_system/n3ILE99s">radio and WiFi positioning systems</a>, and the use of <a href="/facts/Satellite_navigation_system/lVgPlF5v">satellite navigation systems</a>. </p><p>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 <a href="/facts/Two_dimensional/f4b397W8">two-dimensional</a> plane. In practice, observations are subject to errors resulting from various physical and atmospheric factors that influence the measurement of distances and angles.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p><p>A practical example of obtaining a position fix would be for a ship to take <a href="/facts/Bearing_(navigation)/rE84IorW">bearing</a> measurements on three <a href="/facts/Lighthouse/HAwW4RFW">lighthouses</a> positioned along the coast. These measurements could be made visually using a <a href="/facts/Hand_compass/K4pX8FIU">hand bearing compass</a>, or in case of poor visibility, electronically using <a href="/facts/Radar/jk9BTbFA">radar</a> or <a href="/facts/Direction_finding/pAtU7f0I">radio direction finding</a>. 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.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> 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 <a href="/facts/Equilateral_triangle/MJomsYDS">equilateral triangle</a>. <a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> The area of doubt surrounding a position fix is called an <a href="/facts/Error_ellipse/8wJdMBtg">error ellipse</a>. To minimize the error, <a href="/facts/Satellite_navigation/lVgPlF5v">electronic navigation</a> systems generally use more than three reference points to compute a position fix to increase the <a href="/facts/Data_redundancy/k8SCyw0J">data redundancy</a>. As more redundant reference points are added, the position fix becomes more accurate and the area of the resulting error ellipse decreases.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>The process of using 3 reference points to calculate the location is called <a href="/facts/Trilateration/2Jghv9zm">Trilateration</a>, and when using more than 3 points, <i>multilateration</i>. </p><p>Combining multiple observations to compute a position fix is equivalent to solving a system of <a href="/facts/Linear_equations/JfCgALwf">linear equations</a>. Navigation systems use <a href="/facts/Regression_analysis/n6z5Tf7K">regression algorithms</a> such as <a href="/facts/Least_squares/50jIwbxC">least squares</a> in order to compute a position fix in 3D space. This is most commonly done by combining distance measurements to 4 or more <a href="/facts/GPS/DKVLnzF3">GPS</a> <a href="/facts/Satellites/PTX8c68t">satellites</a>, which orbit the Earth along known paths.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <p>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. <a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> In nautical <a href="/facts/Navigation/sGGAJ0AQ">navigation</a>, the term is generally used with manual or visual techniques, such as the use of intersecting visual or radio <a href="/facts/Position_line/KVdYVLCc">position lines</a>, rather than the use of more automated and accurate electronic methods like <a href="/facts/GPS/DKVLnzF3">GPS</a>; in aviation, use of electronic navigation aids is more common. A visual fix can be made by using any sighting device with a <a href="/facts/Bearing_(navigation)/rE84IorW">bearing</a> 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. </p><p>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 <a href="/facts/Dead_reckoning/sljJ7nCT">dead reckoning</a>, which relies on estimates of <a href="/facts/Speed/I3qgMPfs">speed</a> and <a href="/facts/Course_(navigation)/CWexuXNF">course</a>. 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. </p> <h3>Indoor geopositioning</h3> <p class="note">Main article: <a href="/facts/Indoor_positioning_system/sjHxRKGp">Indoor positioning system</a></p> <p>Geopositioning can be referred to both global positioning and outdoor positioning, using for example <a href="/facts/Global_Positioning_System/DKVLnzF3">GPS</a>, 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.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Attitude_determination/hE6aMu26">Attitude determination</a></li> <li><a href="/facts/Direction_determination/8YEzMAtU">Direction determination</a></li> <li><a href="/facts/Dynamic_positioning/ldIHFKj7">Dynamic positioning</a></li> <li><a href="/facts/Geo-blocking/D1tHgYp0">Geo-blocking</a></li> <li><a href="/facts/Geocoding/KtTELe73">Geocoding</a></li> <li><a href="/facts/Geodetic_positioning/EJH0Te0m">Geodetic positioning</a></li> <li><a href="/facts/GPS_tracking_unit/7E082t8Y">GPS tracking unit</a></li> <li><a href="/facts/Geotagging/LuvNUMVA">Geotagging</a></li> <li><a href="/facts/Geotargeting/96srh0WW">Geotargeting</a></li> <li><a href="/facts/Indoor_positioning/sjHxRKGp">Indoor positioning</a></li> <li><a href="/facts/Latitude_determination/IBYqkjhU">Latitude determination</a></li> <li><a href="/facts/Longitude_determination/HsC61ML9">Longitude determination</a></li> <li><a href="/facts/Location-based_service/BXzwkD4d">Location-based service</a></li> <li><a href="/facts/Satellite_navigation_software/vrFqxfhE">Satellite navigation software</a></li> <li><a href="/facts/Triangulation/lpmlmhGd">Triangulation</a></li> <li><a href="/facts/Vertical_position/HpaNYcWC">Vertical position measurement</a></li> <li><a href="/facts/W3C_Geolocation_API/z9Vj53zy">W3C Geolocation API</a></li></ul> <h2 id="further-reading">Further reading</h2> <ul><li>Zekavat, R.; Buehrer, R.M. (2019). <a href="https://www.wiley.com/en-us/9781119434603"><i>Handbook of Position Location: Theory, Practice, and Advances</i></a>. IEEE Series on Digital & Mobile Communication. Wiley. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-119-43460-3. Retrieved 2021-02-19.[<i>permanent dead link</i>]</li> <li>Munoz, D.; Lara, F.B.; Vargas, C.; Enriquez-Caldera, R. (2009). <a href="https://books.google.com/books?id=2sWdiZainyoC"><i>Position Location Techniques and Applications</i></a>. Elsevier Science. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-08-092193-8. Retrieved 2021-02-19.</li></ul> <h2 id="external-links">External links</h2> <ul><li> Media related to Geolocation at Wikimedia Commons</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"geopositioning". ISO/TC 211 Geolexica. 2020-06-02. Retrieved 2020-08-31. <a href="https://isotc211.geolexica.org/concepts/2467/" target="_blank">https://isotc211.geolexica.org/concepts/2467/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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. <a href="https://books.google.com/books?id=m0juAAAAMAAJ&pg=PA5" target="_blank">https://books.google.com/books?id=m0juAAAAMAAJ&pg=PA5</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"What is geofencing and how is it used? – TechTarget Definition". WhatIs. Retrieved 2024-09-10. <a href="https://www.techtarget.com/whatis/definition/geofencing" target="_blank">https://www.techtarget.com/whatis/definition/geofencing</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>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. <a href="978-3-7091-6078-7" target="_blank">978-3-7091-6078-7</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>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. <a href="978-1-4614-1836-8" target="_blank">978-1-4614-1836-8</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Progri, I. (2011). Geolocation of RF Signals: Principles and Simulations. Springer New York. ISBN 978-1-4419-7952-0. Retrieved 2020-08-31. <a href="978-1-4419-7952-0" target="_blank">978-1-4419-7952-0</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>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. <a href="978-1-118-74368-3" target="_blank">978-1-118-74368-3</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Laurie Tetley; David Calcutt (7 June 2007). Electronic Navigation Systems. Routledge. pp. 9–. ISBN 978-1-136-40725-3. <a href="978-1-136-40725-3" target="_blank">978-1-136-40725-3</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>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. <a href="978-3-319-25781-5" target="_blank">978-3-319-25781-5</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>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. <a href="https://doi.org/10.1155%2F2017%2F2630413" target="_blank">https://doi.org/10.1155%2F2017%2F2630413</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> </ol>