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The Geodesy Portal

GPS Block II-F satellite in Earth orbit

Geodesy (/dʒiːˈɒdɪsi/, jee-OD-iss-ee) or geodetics is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D space. It is called planetary geodesy when studying other astronomical bodies, such as planets or circumplanetary systems. Geodetic job titles include geodesist and geodetic surveyor.

Through highly accurate observations, geodesy provides the scientific basis for mapping, navigation, and positioning, and supports applications such as infrastructure development (including construction), natural resource management, mineral exploration, and geophysics. Its measurements underpin modern geospatial reference frames used in transportation, satellite systems, global trade, and timekeeping. (Full article...)

Selected images

Image 1Visual fix by three bearings plotted on a nautical chart (from Geopositioning)
Image 2The Tabula Rogeriana, drawn by Muhammad al-Idrisi for Roger II of Sicily in 1154. South is at the top. (from Cartography)
Image 3Gravity measurement devices, pendulum (left) and absolute gravimeter (right) (from Geodesy)
Image 4Axial tilt (or Obliquity), rotation axis, plane of orbit, celestial equator and ecliptic. Earth is shown as viewed from the Sun; the orbit direction is counter-clockwise (to the left). (from Geodesy)
Image 5Variations in the gravity field of the Moon, from NASA (from Geodesy)
Image 6A modern instrument for geodetic measurements using satellites (from Geodesy)
Image 7Geoid, an approximation for the shape of the Earth; shown here with vertical exaggeration (10000 vertical scaling factor). (from Geodesy)
Image 8Valcamonica rock art (I), Paspardo r. 29, topographic composition, 4th millennium BCE (from Cartography)
Image 9GPS Block IIA satellite orbits over the Earth. (from Geodesy)
Image 10Plot of latitude versus tangential speed. The dashed line shows the Kennedy Space Center example. The dot-dash line denotes typical airliner cruise speed. (from Earth's rotation)
Image 11Principles of geolocation using GPS (from Geopositioning)
Image 12Copy (1472) of St. Isidore's TO map of the world. (from Cartography)
Image 13Topographic map of Easter Island (from Cartography)
Image 142D grid for elliptical coordinates (from Geodesy)
Image 15Navigation device, Apollo program (from Geodesy)
Image 16Ellipsoid - a mathematical representation of the Earth. When mapping in geodetic coordinates, a latitude circle forms a truncated cone. (from Geodesy)
Image 17A stylized map inspired by Renaissance cartographic traditions, created using GIS technology and complemented by a hand-crafted linocut. (from Cartography)
Image 18The cartographic process (from Cartography)
Image 19Illustrated map (from Cartography)
Image 20On a prograde planet like Earth, the stellar day is shorter than the solar day. At time 1, the Sun and a certain distant star are both overhead. At time 2, the planet has rotated 360 degrees and the distant star is overhead again but the Sun is not (1→2 = one stellar day). It is not until a little later, at time 3, that the Sun is overhead again (1→3 = one solar day). (from Earth's rotation)
Image 21Geodetic control mark (from Geodesy)
Image 22Areal distortion caused by Mercator projection (from Cartography)
Image 23A 14th-century Byzantine map of the British Isles from a manuscript of Ptolemy's Geography, using Greek numerals for its graticule: 52–63°N of the equator and 6–33°E from Ptolemy's Prime Meridian at the Fortunate Isles. (from Cartography)
Image 24Relief map Sierra Nevada (from Cartography)
Image 25The Bedolina Map and its tracing, 6th–4th century BCE (from Cartography)
Image 26Europa regina in Sebastian Münster's "Cosmographia", 1570 (from Cartography)
Image 27Earth's gravity measured by NASA GRACE mission, showing deviations from the theoretical gravity of an idealized, smooth Earth ellipsoid. The deviations toward stronger gravity are colored red; deviations toward weaker gravity are colored blue. (from Gravity of Earth)
Image 28Small section of an orienteering map (from Cartography)
Image 29A simulated history of Earth's day length, depicting a resonant-stabilizing event throughout the Precambrian era (from Earth's rotation)
Image 30The definition of latitude (φ) and longitude (λ) on an ellipsoid of revolution (or spheroid). The graticule spacing is 10 degrees. The latitude is defined as the angle between the normal to the ellipsoid and the equatorial plane. (from Geodesy)
Image 31Global plate tectonic movement using GPS (from Geodesy)
Image 32Deviation of day length from SI-based day (from Earth's rotation)
Image 33Global Satellite Navigation System (GNSS) orbits and comparison (from Geomatics)
Image 34Datum shift between NAD27 and NAD83, in metres (from Geodesy)
Image 35How very-long-baseline interferometry (VLBI) works (from Geodesy)
Image 36A plumb bob determines the local vertical direction (from Gravity of Earth)
Image 37A Munich archive with lithography plates of maps of Bavaria (from Geodesy)
Image 38This long-exposure photo of the northern night sky above the Nepali Himalayas shows the apparent paths of the stars as Earth rotates. (from Earth's rotation)
Image 39A pre-Mercator nautical chart of 1571, from Portuguese cartographer Fernão Vaz Dourado (c. 1520 – c. 1580). It belongs to the so-called plane chart model, where observed latitudes and magnetic directions are plotted directly into the plane, with a constant scale, as if the Earth were a plane (Portuguese National Archives of Torre do Tombo, Lisbon). (from Cartography)
Image 40An artist's rendering of the protoplanetary disk (from Earth's rotation)
Image 41Mapping can be done with GPS and laser rangefinder directly in the field. Image shows mapping of forest structure (position of trees, dead wood and canopy). (from Cartography)
Earth's gravity vs. distance from it, from the surface to 30000 km (from Gravity of Earth)
Image 43Earth's axial tilt is about 23.4°. It oscillates between 22.1° and 24.5° on a 41,000-year cycle and is currently decreasing. (from Earth's rotation)
Image 44Equatorial ( $a$ ), polar ( $b$ ) and mean Earth radii as defined in the 1984 World Geodetic System (from Geodesy)
Image 45Gravity at different internal layers of Earth (1 = continental crust, 2 = oceanic crust, 3 = upper mantle, 4 = lower mantle, 5+6 = core, A = crust-mantle boundary) (from Gravity of Earth)
Image 46Earth's rotation imaged by Deep Space Climate Observatory (from Earth's rotation)
Image 47Starry circles arc around the south celestial pole, seen overhead at ESO's La Silla Observatory. (from Earth's rotation)
Image 48Height measurement using satellite altimetry (from Geodesy)
Image 49A relative gravimeter (from Geodesy)
Image 50Image of the canyonlands generated using TruFlite and displays hues of green, blue, and yellow for elevation. - Martin D. Adamiker (from Geomatics)

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v t e Geodesy
Overview	Geodesists History Timeline
Subfields	Cartography Computer cartography Web mapping Earth's orbit Geodetic astronomy Geomatics Gravity of Earth Navigation Photogrammetry Remote Sensing Geopositioning Virtual globe
Physical phenomena	Chandler wobble Coriolis effect Earth's energy budget Earth's gravity field Geodynamo Gravity of Earth Plate tectonics Precession of the equinoxes Tide
Related disciplines	Astronomy Geology Geophysics Mathematics Physics
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