Editing Geodesy (section)

== Positioning ==
{{see also|Geodetic network#Measurement techniques}}
{{unsourced section|date=February 2024}}
[[File:GPS satellite approaching 23 years on orbit (1060259).jpeg|220px|thumb|right|[[GPS]] Block IIA satellite orbits over the [[Earth]].]]
[[File:Geodetic Control Mark.jpg|220px|thumb|Geodetic control mark]]
[[File:Apollo IMU at Draper Hack the Moon exhibit.agr.jpg|220px|thumb|right|[[Inertial navigation|Navigation]] device, [[Apollo program]]]]

General [[geopositioning]], or simply positioning, is the determination of the location of points on Earth, by myriad techniques. '''Geodetic positioning''' employs geodetic methods to determine a set of precise geodetic coordinates of a point on land, at sea, or in space. It may be done within a coordinate system ('''point positioning''' or '''absolute positioning''') or relative to another point ('''relative positioning'''). One computes the position of a point in space from measurements linking terrestrial or extraterrestrial points of known location ("known points") with terrestrial ones of unknown location ("unknown points"). The computation may involve transformations between or among astronomical and terrestrial coordinate systems. Known points used in point positioning can be [[Global Navigation Satellite Systems|GNSS]] [[continuously operating reference station]]s or [[Triangulation (surveying)|triangulation points]] of a higher-order network.

Traditionally, geodesists built a hierarchy of networks to allow point positioning within a country. The highest in this hierarchy were triangulation networks, densified into the networks of [[traverse (surveying)|traverse]]s ([[polygons]]) into which local mapping and surveying measurements, usually collected using a measuring tape, a [[Corner reflector|corner prism]], and the red-and-white poles, are tied.

Commonly used nowadays is GPS, except for specialized measurements (e.g., in underground or high-precision engineering). The higher-order networks are measured with [[Global Positioning System|static GPS]], using [[Differential GPS|differential measurement]] to determine vectors between terrestrial points. These vectors then get adjusted in a traditional network fashion. A global polyhedron of permanently operating GPS stations under the auspices of the [[IERS]] is the basis for defining a single global, geocentric reference frame that serves as the "zero-order" (global) reference to which national measurements are attached.

[[Real-time kinematic positioning]] (RTK GPS) is employed frequently in [[surveying|survey]] mapping. In that measurement technique, unknown points can get quickly tied into nearby terrestrial known points.

One purpose of point positioning is the provision of known points for mapping measurements, also known as (horizontal and vertical) control. There can be thousands of those geodetically determined points in a country, usually documented by national mapping agencies. Surveyors involved in real estate and insurance will use these to tie their local measurements.