Portal:Geodesy
The Geodesy Portal
Geodesy or geodetics is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D. It is called planetary geodesy when studying other astronomical bodies, such as planets or circumplanetary systems. Geodesy is an earth science as well as a discipline of applied mathematics, and many consider the study of Earth's shape and gravity to be central to the science.
Geodynamical phenomena, including crustal motion, tides, and polar motion, can be studied by designing global and national control networks, applying space geodesy and terrestrial geodetic techniques, and relying on datums and coordinate systems. Geodetic job titles include geodesist and geodetic surveyor. (Full article...)
Selected images
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gravity anomaly animation over oceans from the NASA's GRACE (Gravity Recovery and Climate Experiment) (from Geodesy)Global
- A plumb bob determines the local vertical direction (from
- A simulated history of Earth's day length, depicting a resonant-stabilizing event throughout the Precambrian era (from
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Sierra Nevada (from Cartography)Relief map
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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)A pre-Mercator nautical chart of 1571, from Portuguese cartographer
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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)Earth's
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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)This
- Principles of geolocation using GPS (from
- Copy (1472) of
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Bedolina Map and its tracing, 6th–4th century BCE (from Cartography)The
- Starry circles arc around the south celestial pole, seen overhead at
- Height measurement using satellite altimetry (from
- A
- A map of recent volcanic activity and ridge spreading. The areas where NASA GRACE measured gravity to be stronger than the theoretical gravity have a strong correlation with the positions of the volcanic activity and ridge spreading. (from
- The 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
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total station (from Geomatics)Surveyor using a
- Variations in the gravity field of the
- Small section of an orienteering map (from
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Tabula Rogeriana, drawn by Muhammad al-Idrisi for Roger II of Sicily in 1154. South is at the top. (from Cartography)The
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Deep Space Climate Observatory, showing axistilt (from Earth's rotation)Earth's rotation imaged by
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GPS and laser rangefinder directly in the field. Image shows mapping of forest structure (position of trees, dead wood and canopy). (from Cartography)Mapping can be done with
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Geoid, an approximation for the shape of the Earth; shown here with vertical exaggeration (10000 vertical scaling factor). (from Geodesy)
- 2D grid for elliptical coordinates (from
- Datum shift between
- Illustrated map (from
- Gravity measurement devices, pendulum (left) and absolute gravimeter (right) (from
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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)On a
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Easter Island (from Cartography)Topographic map of
- The cartographic process (from
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Mercator projection (from Cartography)Areal distortion caused by
- Geodetic control mark (from
- Visual fix by three bearings plotted on a nautical chart (from
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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)A 14th-century
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Valcamonica rock art (I), Paspardo r. 29, topographic composition, 4th millennium BCE (from Cartography)
- A modern instrument for geodetic
- Gravity 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
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Kennedy Space Center example. The dot-dash line denotes typical airliner cruise speed. (from Earth's rotation)Plot of latitude versus tangential speed. The dashed line shows the
- Axial tilt (or
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very-long-baseline interferometry (VLBI) works (from Geodesy)How
- An artist's rendering of the
- A relative gravimeter (from
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GRACE mission, showing deviations from the theoretical gravity of an idealized, smooth Earth, the so-called Earth ellipsoid. Red shows the areas where gravity is stronger than the smooth, standard value, and blue reveals areas where gravity is weaker (Animated version). (from Gravity of Earth)Earth's gravity measured by NASA
- Deviation of day length from SI-based day (from
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Ecumene (1482, Johannes Schnitzer, engraver), constructed after the coordinates in Ptolemy's Geography and using his second map projection. The translation into Latin and dissemination of Geography in Europe, in the beginning of the 15th century, marked the rebirth of scientific cartography, after more than a millennium of stagnation. (from Cartography)A medieval depiction of the
- Equatorial (
- Global plate tectonic movement using GPS (from
- Initial acquisition of GPS signal in 2D (from
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