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.
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.
Amsterdam Ordnance Datum or Normaal Amsterdams Peil (NAP) is a vertical datum in use in large parts of Western Europe. Originally created for use in the Netherlands, its height was used by Prussia in 1879 for defining Normalnull, and in 1955 by other European countries. In the 1990s, it was used as the reference level for the United European leveling Network (UELN) which in turn led to the European Vertical Reference System (EVRS).
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.
The vertical deflection at a point on the Earth is a measure of how far the gravity direction has been shifted by local anomalies such as nearby mountains. They are widely used in geodesy, for surveying networks and for geophysical purposes.
A geodetic datum or geodetic system is a coordinate system, and a set of reference points, used for locating places on the Earth. An approximate definition of sea level is the datum WGS 84, an ellipsoid, whereas a more accurate definition is Earth Gravitational Model 2008 (EGM2008), using at least 2,159 spherical harmonics. Other datums are defined for other areas or at other times; ED50 was defined in 1950 over Europe and differs from WGS 84 by a few hundred meters depending on where in Europe you look. Mars has no oceans and so no sea level, but at least two martian datums have been used to locate places there.
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.
The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface . The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface.
EUREF Permanent Network (EPN) is a European Network of more than 300 continuously operating GNSS reference stations with precisely known coordinates referenced to the ETRS89. EPN 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. EPN is created and maintained by a voluntary agreement of about 100 European agencies and universities. EPN activities are coordinated by EUREF.
The term benchmark, or bench mark, originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle-iron could be placed to form a "bench" for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in the future. These marks were usually indicated with a chiseled arrow below the horizontal line.
Norge 1:50 000 is the main series of 727 topographical maps in 1:50,000 scale that cover the entire mainland area of Norway and proximate islands. The civilian designation is Norway 1:50 000 and the military designation is M711.
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 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.
A vertical datum or height datum is a reference surface for vertical positions, such as the elevations of Earth features including terrain, bathymetry, water level, and man-made structures; in any particular case one must be assigned even if arbitrarily, and commonly adopted criteria for a vertical datum include the following approaches:
European Combined Geodetic Network (ECGN) is a research project aimed at high accuracy geoid determination. The purpose of ECGN is to connect the height systems obtained via geometric positioning by GNSS with gravity-referenced heights with a cm-level accuracy. The effects of the atmosphere, the oceans and time-dependent parameters of the solid Earth on the gravity field are investigated. ECGN uses the data of satellite gravity missions CHAMP, GRACE and GOCE to model the Earth's gravity field and is linked to other gravity-related projects. The ECGN is considered as a European contribution to the International Association of Geodesy (IAG) project Global Geodetic Observation System (GGOS). ECGN is managed by EUREF.
Normalhöhennull or NHN is a vertical datum used in Germany.
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 or 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).
The Luzon Datum of 1911 was the base for the first modern survey of the Philippine Islands. The execution of the triangulation of the Philippine Islands extended over almost as long a time as the history of the American occupation in the Philippines. The plan of the government to survey the islands began in March 1900 when a United States Coast and Geodetic Survey (USCGS) officer was sent to Manila with instructions to prepare a report on the existing cartographic conditions in the Philippines and to obtain all information necessary for the execution of geodetic, hydrographic, and topographic surveys in the country.
The Datum of 2022 is a placeholder name for a new vertical datum set to be produced by the National Geodetic Survey in 2022 to improve the National Spatial Reference System (NSRS) by replacing the North American Datum of 1983 and the North American Vertical Datum of 1988 with a new geometric reference frame and geopotential datum.
