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The African Geodetic Reference Frame (AFREF) is a project designed to unify the many geodetic reference frames of Africa using data from a network of permanent Global Navigation Satellite Systems (GNSS) stations as the primary data source for the implementation of a uniform reference frame. [1]
Geodesy is the Earth science of accurately measuring and understanding Earth's geometric shape, orientation in space and gravitational field. The field also incorporates studies of how these properties change over time and equivalent measurements for other planets. Geodynamical phenomena include crustal motion, tides and polar motion, which can be studied by designing global and national control networks, applying space and terrestrial techniques and relying on datums and coordinate systems.
A geographic coordinate system (GCS) is a coordinate system associated with positions on Earth. A GCS can give positions:
The World Geodetic System (WGS) is a standard for use in cartography, geodesy, and satellite navigation including GPS. This standard includes the definition of the coordinate system's fundamental and derived constants, the ellipsoidal (normal) Earth Gravitational Model (EGM), a description of the associated World Magnetic Model (WMM), and a current list of local datum transformations.
Gravity Probe B (GP-B) was a satellite-based experiment to test two unverified predictions of general relativity: the geodetic effect and frame-dragging. This was to be accomplished by measuring, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth-orbiting satellite at 650 km (400 mi) altitude, crossing directly over the poles.
In satellite laser ranging (SLR) a global network of observation stations measures the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors. This provides instantaneous range measurements of millimeter level precision which can be accumulated to provide accurate measurement of orbits and a host of important scientific data. The laser pulse can also be reflected by the surface of a satellite without a retroreflector, which is used for tracking space debris.
The International Terrestrial Reference System (ITRS) describes procedures for creating reference frames suitable for use with measurements on or near the Earth's surface. This is done in much the same way that a physical standard might be described as a set of procedures for creating a realization of that standard. The ITRS defines a geocentric system of coordinates using the SI system of measurement.
A geodetic datum or geodetic system is a global datum reference or reference frame for precisely measuring locations on Earth or other planetary body. Datums are crucial to any technology or technique based on spatial location, including geodesy, navigation, surveying, geographic information systems, remote sensing, and cartography. A Horizontal datum is used to measure a location across the Earth's surface, in latitude and longitude or another coordinate system; a vertical datum is used to measure the elevation or depth relative to a standard origin, such as mean sea level (MSL). Since the rise of the global positioning system (GPS), the ellipsoid and datum WGS 84 it uses has supplanted most others in many applications. The WGS 84 is intended for global use, unlike most earlier datums.
The European Terrestrial Reference System 1989 (ETRS89) is an ECEF geodetic Cartesian reference frame, in which the Eurasian Plate as a whole is static. The coordinates and maps in Europe based on ETRS89 are not subject to change due to the continental drift.
Satellite geodesy is geodesy by means of artificial satellites — the measurement of the form and dimensions of Earth, the location of objects on its surface and the figure of the Earth's gravity field by means of artificial satellite techniques. It belongs to the broader field of space geodesy. Traditional astronomical geodesy is not commonly considered a part of satellite geodesy, although there is considerable overlap between the techniques.
EUREF Permanent Network (EPS) is a European network of more than 300 continuously operating GNSS reference stations with precisely known coordinates referenced to the ETRS89. EPS is the key instrument in the maintenance of ETRS89 geodetic datum. The EPN stations collect continuously the observation data from high accuracy multi-GNSS receivers. The data is processed in the centralized way in a few data processing centres. EPS is created and maintained by a voluntary agreement of about 100 European agencies and universities. EPS activities are coordinated by EUREF.
The North American Datum (NAD) is the horizontal datum now used to define the geodetic network in North America. A datum is a formal description of the shape of the Earth along with an "anchor" point for the coordinate system. In surveying, cartography, and land-use planning, two North American Datums are in use for making lateral or "horizontal" measurements: the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83). Both are geodetic reference systems based on slightly different assumptions and measurements.
The North American Vertical Datum of 1988 is the vertical datum for orthometric heights established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.
An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximations.
The term fundamental station is used for special observatories which combine several space positioning techniques like VLBI, satellite laser ranging, GPS, Glonass, etc. They are the basis of plate tectonic analysis, allowing the monitoring of continental drift rates with millimetre accuracies. A fundamental point is the geometric origin of a geodetic network and defines the geodetic datum of a national survey.
Regional Reference Frame Sub-Commission for Europe (EUREF) is the sub-commission of the International Association of Geodesy (IAG), part of the Sub-Commission 1.3, under IAG Commission 1 . EUREF deals with the definition, realization and maintenance of the European Geodetic Reference Frame. The goal of EUREF is to establish a unified geodetic datum (ETRS89) and a consistent network of reference stations (EPN) throughout Europe. EUREF was founded in 1987 at the IUGG General Assembly held in Vancouver.
The National Spatial Reference System (NSRS), managed by the National Geodetic Survey (NGS), is a coordinate system that includes latitude, longitude, elevation, and other values. The NSRS consists of a National Shoreline, the National CORS, a network of permanently marked points, and a set of models that describe dynamic geophysical processes affecting spatial measurements.
UNAVCO is a non-profit university-governed consortium that facilitates geoscience research and education using Geodesy. UNAVCO is funded by the National Science Foundation (NSF) and The National Aeronautics and Space Administration (NASA) to support geoscience research around the world. UNAVCO operates the GAGE Facility on behalf of the NSF and NASA. As a university-governed consortium, UNAVCO supports the goals of the academic scientific community. UNAVCO has 120 US academic members and supports over 110 organizations globally as associate members.
The Geospatial Information Authority of Japan, or GSI, is the national institution responsible for surveying and mapping the national land of Japan. The former name of the organization from 1949 until March 2010 was Geographical Survey Institute. It is an extraordinary organ of the Ministry of Land, Infrastructure, Transport and Tourism. Its main offices are situated in Tsukuba City of Ibaraki Prefecture.
The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the prime meridian maintained by the International Earth Rotation and Reference Systems Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle which is 102 metres (335 ft) at the latitude of the Royal Observatory, Greenwich. It is also the reference meridian of the Global Positioning System (GPS) operated by the United States Department of Defense, and of WGS84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).
EPSG Geodetic Parameter Dataset is a public registry of geodetic datums, spatial reference systems, Earth ellipsoids, coordinate transformations and related units of measurement. Each entity is assigned an EPSG code between 1024-32767, along with a standard machine-readable well-known text (WKT) representation. The dataset is actively maintained by the IOGP Geomatics Committee.
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