# Geodesy

geodeticgeodesistgeodesicgeodetic surveygeodetic surveyinggeodeticalgeodesistsgeodetic pointgeodetic surveysarchaeogeodesy
Geodesy, is the earth science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravitational field.wikipedia
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### Reference ellipsoid

ellipsoidexact size and shapeAiry ellipsoid
The geoid, unlike the reference ellipsoid, is irregular and too complicated to serve as the computational surface on which to solve geometrical problems like point positioning.
In geodesy, a reference ellipsoid is a mathematically defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body.

### Geodetic control network

geodetic networkcontrol networkgeodetic networks
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 scientific discipline that deals with the establishing of coordinates of points in a high-order control network is called geodesy, and the technical discipline that does the same for points in a low-order control network is called surveying.

### Physical geodesy

gravity fieldGeodesygravity
For this reason, the study of the Earth's gravity field is called physical geodesy.
Physical geodesy is the study of the physical properties of the gravity field of the Earth, the geopotential, with a view to their application in geodesy.

### Satellite geodesy

satellite altimetrygeodeticAltimetry
Prior to the era of satellite geodesy, the coordinate systems associated with a geodetic datum attempted to be geocentric, but their origins differed from the geocenter by hundreds of meters, due to regional deviations in the direction of the plumbline (vertical).
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.

### Earth science

geoscienceearth sciencesgeosciences
Geodesy, is the earth science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravitational field.
Geophysics and geodesy investigate the shape of the Earth, its reaction to forces and its magnetic and gravity fields. Geophysicists explore the earth's core and mantle as well as the tectonic and seismic activity of the lithosphere. Geophysics is commonly used to supplement the work of geologists in developing a comprehensive understanding of crustal geology, particularly in mineral and petroleum exploration. Seismologists use geophysics to understand plate tectonic shifting, as well as predict seismic activity.

### Geodetic datum

datumGeodeticinitial point
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. Prior to the era of satellite geodesy, the coordinate systems associated with a geodetic datum attempted to be geocentric, but their origins differed from the geocenter by hundreds of meters, due to regional deviations in the direction of the plumbline (vertical).
Datums are used in geodesy, navigation, and surveying by cartographers and satellite navigation systems to translate positions indicated on maps (paper or digital) to their real position on Earth.

### International Union of Geodesy and Geophysics

IUGGInternational Association of Seismology and Physics of the Earth's InteriorInternational Union of Geodesy and Geophysics (IUGG)
This system was adopted at the XVII General Assembly of the International Union of Geodesy and Geophysics (IUGG).
The International Union of Geodesy and Geophysics (IUGG; Union géodésique et géophysique internationale, UGGI) is an international non-governmental organisation dedicated to the scientific study of the Earth and its space environment using geophysical and geodetic techniques.

### Earth

terrestrialworldGlobal
Geodesy, is the earth science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravitational field.
In geodesy, the exact shape that Earth's oceans would adopt in the absence of land and perturbations such as tides and winds is called the geoid.

### Geoid

geodetic sea levelvaries slightlygeoids
The geoid is essentially the figure of the Earth abstracted from its topographical features. These regional geodetic data, such as ED 50 (European Datum 1950) or NAD 27 (North American Datum 1927) have ellipsoids associated with them that are regional "best fits" to the geoids within their areas of validity, minimizing the deflections of the vertical over these areas.
Despite being an important concept for almost 200 years in the history of geodesy and geophysics, it has been defined to high precision only since advances in satellite geodesy in the late 20th century.

### North American Datum

These regional geodetic data, such as ED 50 (European Datum 1950) or NAD 27 (North American Datum 1927) have ellipsoids associated with them that are regional "best fits" to the geoids within their areas of validity, minimizing the deflections of the vertical over these areas.
The North American Datum (NAD) is the datum now used to define the geodetic network in North America.

### Geodetic Reference System 1980

1980 Geodetic Reference SystemGeodetic Reference System 1980 (GRS 80)GRS 80
The 1980 Geodetic Reference System (GRS 80) posited a 6,378,137 m semi-major axis and a 1:298.257 flattening.
Geodesy is the scientific discipline that deals with the measurement and representation of the earth, its gravitational field and geodynamic phenomena (polar motion, earth tides, and crustal motion) in three-dimensional, time-varying space.

### Helmert transformation

Helmert datum transformation
In the plane, a Helmert transformation has four parameters; in space, seven.
It is frequently used in geodesy to produce distortion-free transformations from one datum to another.

### Geodesic

geodesicsgeodesic flowgeodesic equation
In the general case, the solution is called the geodesic for the surface considered.
The term "geodesic" comes from geodesy, the science of measuring the size and shape of Earth; in the original sense, a geodesic was the shortest route between two points on the Earth's surface, namely, a segment of a great circle.

### Vincenty's formulae

VincentyVincenty formula
On the ellipsoid of revolution, geodesics may be written in terms of elliptic integrals, which are usually evaluated in terms of a series expansion—see, for example, Vincenty's formulae.
Vincenty's formulae are two related iterative methods used in geodesy to calculate the distance between two points on the surface of a spheroid, developed by Thaddeus Vincenty (1975a).

### Traverse (surveying)

traverseTraversingsurvey
These were densified into networks of traverses (polygons), into which local mapping surveying measurements, usually with measuring tape, corner prism, and the familiar red and white poles, are tied.
It is also used in geodesy.

### World Geodetic System

WGS84World Geodetic System 84GPS Coordinates
Such a frame is, e.g., WGS84, or the frames that are regularly produced and published by the International Earth Rotation and Reference Systems Service (IERS).
The World Geodetic System (WGS) is a standard for use in cartography, geodesy, and satellite navigation including GPS.

### Sidereal time

sidereal daysidereallocal sidereal time
The coordinate transformation between these two systems is described to good approximation by (apparent) sidereal time, which takes into account variations in the Earth's axial rotation (length-of-day variations).
For this reason, to simplify the description of Earth's orientation in astronomy and geodesy, it was conventional to chart the positions of the stars in the sky according to right ascension and declination, which are based on a frame that follows Earth's precession, and to keep track of Earth's rotation, through sidereal time, relative to this frame as well.

Interferometric synthetic aperture radar (InSAR) using satellite images
Interferometric synthetic aperture radar, abbreviated InSAR (or deprecated IfSAR), is a radar technique used in geodesy and remote sensing.

### Satellite laser ranging

laser rangingSLRILRS
For planet-wide geodetic surveys, previously impossible, we can still mention satellite laser ranging (SLR) and lunar laser ranging (LLR) and very-long-baseline interferometry (VLBI) techniques.
Satellite laser ranging is a proven geodetic technique with significant potential for important contributions to scientific studies of the earth/atmosphere/ocean system.

### Height

tallhhigh
In geodesy, point or terrain heights are "above sea level", an irregular, physically defined surface.
In practice, the sea level under a continent has to be computed from gravity measurements, and slightly different computational methods exist; see Geodesy, heights.

### Gravimeter

gravimetersgravimetricgravitometer
Gravity is measured using gravimeters, of which there are two kinds.
Gravimeters are used for petroleum and mineral prospecting, seismology, geodesy, geophysical surveys and other geophysical research, and for metrology.

### Latitude

Southlatitudeslatitudinal
Geographical latitude and longitude are stated in the units degree, minute of arc, and second of arc. They are angles, not metric
The study of the figure of the Earth together with its gravitational field is the science of geodesy.

### Very-long-baseline interferometry

very long baseline interferometryVLBIlong-baseline interferometry
For planet-wide geodetic surveys, previously impossible, we can still mention satellite laser ranging (SLR) and lunar laser ranging (LLR) and very-long-baseline interferometry (VLBI) techniques.
However, since the VLBI technique measures the time differences between the arrival of radio waves at separate antennas, it can also be used "in reverse" to perform earth rotation studies, map movements of tectonic plates very precisely (within millimetres), and perform other types of geodesy.

### Polar motion

displaced the North PoledriftsEarth polar motion
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.
Geodesy

### Pierre Bouguer

BouguerBouguer, Pierre
Pierre Bouguer 1698–1758, (France & Peru)
Pierre Bouguer (16 February 1698, Croisic – 15 August 1758, Paris) was a French mathematician, geophysicist, geodesist, and astronomer.