|
|
| Line 1: |
Line 1: |
| {{More footnotes|date=February 2009}}
| | == Kanada. Es ist auch möglich Pandora Charms Sale == |
| {{Geodesy}}
| |
| [[File:Geodetisch station1855.jpg|thumb|An old geodetic pillar (1855) at [[Ostend]], [[Belgium]]]]
| |
| [[File:Litography archive of the Bayerisches Vermessungsamt.jpg|thumb|A [[Munich]] archive with [[lithography]] plates of maps of [[Bavaria]]]]
| |
|
| |
|
| '''Geodesy''' ({{IPAc-en|dʒ|iː|ˈ|ɒ|d|ɨ|s|i}}),<ref>''[[Oxford English Dictionary|OED]]''</ref> also named '''geodetics''', a branch of [[applied mathematics]] <ref>[http://www.merriam-webster.com/dictionary/geodesy Merriam-Webster Dictionary]</ref> and [[earth science]]s, is the scientific discipline that deals with the measurement and representation of the [[Earth]], including its [[gravitational field]], in a three-dimensional time-varying space. Geodesists also study [[geodynamics|geodynamic]]al phenomena such as [[crust (geology)|crustal]] motion, [[tide]]s, and [[polar motion]]. For this they design global and national [[control network]]s, using [[Space techniques|space]] and terrestrial techniques while relying on [[datum (geodesy)|datum]]s and [[coordinate system]]s.
| | Dale Carnegie Dale Carnegie war der Gründer der modernen Selbstverbesserung Trainingsprogramm, und er einige dramatische Durchbrüche in der, wie zu coachen und trainieren Menschen geschaffen. In der Tat, entwickelte er eine Coaching-Technik namens Abstand Lern wo er unterrichtete die Teilnehmer für ein paar Stunden pro Woche über eine Reihe von Wochen. <br><br>Sie infizierten die Brand mit Pilz eindringende Viren, aber resistente Stämme weiter, um Bäume zu töten. Paul. Dies bedeutet, dass keine Fahr aus irgendeinem Grund für ein volles Kalenderjahr. Es wird noch schlimmer.. Von unseren Kunden, Spender und Andere Kunden Wenn beim Besuch unserer Website Sie ein Produkt bestellen, registrieren Sie sich für eine Konferenz, senden Sie eine technische Frage Unterstützung oder andere Informationen benötigen, werden Sie gebeten, bestimmte Informationen zu liefern. In allen Fällen erfolgt diese freiwillig einzureichen. <br><br>In der Tat, es gibt über 70.000 befischbaren Seen in Ontario, Lac Seul Angelinformationen auf dem Lac Seul Ontario, Kanada. Lac Seul Trophy Zander angeln und Hecht Angeln in Ontario, Kanada. Es ist auch möglich, dass Sie versehentlich gelöscht haben Ihr Dokument Wurzel oder Ihr Konto muss neu erstellt werden. So [http://www.eyerex.com/net/news/Beschreibung/header.asp?p=26-Pandora-Charms-Sale Pandora Charms Sale] oder so, kontaktieren Sie bitte HostGator sofort per Telefon oder Live-Chat, damit wir die problem.Are diagnostizieren Sie mit Wordpress? Siehe den Abschnitt über die 404-Fehler nach dem Klicken auf einen Link in Wordpress. <br><br>MO Neosho Daily News Gatehouse Media Inc. MO Rolla Daily News Gatehouse Media Inc. Er tat viel besser als gegen die Türkei. Die einzige Kritik, die ich habe, ist, dass er manchmal zu langsam, um für den Ball verlieren Push-up war. Aber ich glaube nicht, dass diejenigen von uns, die Fans von Kristin Veitch sind so viel an immer die Spoiler von ihr. Wir möchten nicht, dass sie ihre TV-Anschlüsse zu riskieren, nur um uns Informationen, die wir erhalten immer eine Woche später von jemand anderem zu geben. <br><br>Küken Angriffe Shriners, Evolution (die "Spur", die mit Lügen [http://www.paint-point.ch/energy/inc/config.asp?a=34-Abercrombie-Switzerland-Office Abercrombie Switzerland Office] gefüllt ist), AIDS, Abtreibung, christlichen [http://www.studerkunststoffe.ch/script/style.asp?p=84-Polo-Ralph-Lauren-Jacke-Big-Pony Polo Ralph Lauren Jacke Big Pony] Kirchen etwas andere Überzeugungen und Halloween. Die Website enthält auch Links als solche "Meet Jesus" und "Kann Regierung fördern Charity Ohne Religion?" . <br><br>Die eigentliche Betrug ist, wenn Sie Leitwährung Status verlieren. Ben will nicht all die 100 $-Scheine kommen wieder nach Hause. [http://www.cattledog-kelpie.ch/infragistics/Images/Large/config.asp?b=28-Beats-By-Dr-Dre Beats By Dr Dre] In Japan, in der Woche vom 24. März 30. Alex Marvez (AP Photo / Michael Keating) .. Das Verfahren, während in einer Antwort oder Erstellen eines neuen Threads ist: Es gibt 2 Möglichkeiten, dies zu tun.<ul> |
| | | |
| == Definition ==
| | <li>[http://hanweifang.com.cn/news/html/?566599.html http://hanweifang.com.cn/news/html/?566599.html]</li> |
| Geodesy (from [[Ancient Greek|Greek]] γεωδαισία, ''geodaisia'', lit. "division of the Earth") is primarily concerned with positioning within the [[time|temporally]] varying gravity field. Somewhat obsolete nowadays, geodesy in the [[German language|German]] speaking world is divided into "Higher Geodesy" ("Erdmessung" or "höhere Geodäsie"), which is concerned with measuring the Earth on the global scale, and "Practical Geodesy" or "Engineering Geodesy" ("Ingenieurgeodäsie"), which is concerned with measuring specific parts or regions of the Earth, and which includes [[surveying]].
| | |
| | | <li>[http://netburst.org/index.php?site=polls&pollID=3 http://netburst.org/index.php?site=polls&pollID=3]</li> |
| The shape of the Earth is to a large extent the result of its rotation, which causes its equatorial bulge, and the competition of geological processes such as the collision of plates and of [[Volcano|volcanism]], resisted by the Earth's [[gravity]] field. This applies to the solid surface, the liquid surface ([[dynamic sea surface topography]]) and the [[Earth's atmosphere]]. For this reason, the study of the Earth's [[gravity field]] is called [[physical geodesy]] by some.
| | |
| | | <li>[http://www.414300.net/news/html/?518251.html http://www.414300.net/news/html/?518251.html]</li> |
| == History ==
| | |
| {{main|History of geodesy}}
| | <li>[http://sylhgy.com/forum.php?mod=viewthread&tid=133415&fromuid=57286 http://sylhgy.com/forum.php?mod=viewthread&tid=133415&fromuid=57286]</li> |
| | | |
| == Geoid and reference ellipsoid ==
| | </ul> |
| {{see also|Geoid}}
| |
| | |
| The [[geoid]] is essentially the figure of the Earth abstracted from its topographical features. It is an idealized equilibrium surface of sea water, the [[mean sea level]] surface in the absence of currents, air pressure variations etc. and continued under the continental masses. 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. The geometrical separation between the geoid and the reference ellipsoid is called the geoidal [[wiktionary:undulate|undulation]]. It varies globally between ±110 m, when referred to the GRS 80 ellipsoid.
| |
| | |
| A [[reference ellipsoid]], customarily chosen to be the same size (volume) as the geoid, is described by its semi-major axis (equatorial
| |
| radius) ''a'' and flattening ''f''. The quantity ''f'' = (''a''−''b'')/''a'', where ''b'' is the semi-minor axis (polar radius), is a purely geometrical one. The mechanical ellipticity of the Earth (dynamical flattening, symbol ''J''<sub>2</sub>) can be determined to high precision by observation of satellite orbit perturbations. Its relationship with the geometrical flattening is indirect. The relationship depends on the internal density distribution, or, in simplest terms, the degree of central concentration of mass.
| |
| | |
| The 1980 Geodetic Reference System ([[GRS80]]) posited a 6,378,137 m semi-major axis and a 1:298.257 flattening. This system was adopted at the XVII General Assembly of the International Union of Geodesy and Geophysics ([[IUGG]]). It is essentially the basis for geodetic positioning by the Global Positioning System and is thus also in widespread use outside the geodetic community.
| |
| | |
| The numerous other systems which have been used by diverse countries for their maps and charts are gradually dropping out of use as more and more countries move to global, geocentric reference systems using the GRS80 reference ellipsoid.
| |
| | |
| == Coordinate systems in space ==
| |
| {{see also|Geodetic system}}
| |
| | |
| The locations of points in three-dimensional space are most conveniently described by three [[cartesian coordinate system|cartesian]] or rectangular coordinates, <math>X, Y</math> and <math>Z</math>. Since the advent of satellite positioning, such coordinate systems are typically [[geocentric]]: the <math>Z</math> axis is aligned with the Earth's (conventional or instantaneous) rotation axis.
| |
| | |
| Prior to the era of [[satellite geodesy]], the coordinate systems associated with a geodetic [[datum (geodesy)|datum]] attempted to be [[geocentric]], but their origins differed from the geocentre by hundreds of metres, due to regional deviations in the direction of the [[plumbline]] (vertical). These regional geodetic datums, such as [[ED50]] (European Datum 1950) or [[North American Datum#North American Datum of 1927|NAD27]] (North American Datum 1927) have ellipsoids associated with them that are regional 'best fits' to the [[geoid]]s within their areas of validity, minimising the deflections of the vertical over these areas.
| |
| | |
| It is only because [[Global Positioning System|GPS]] satellites orbit about the geocentre, that this point becomes naturally the origin of a coordinate system defined by satellite geodetic means, as the satellite positions in space are themselves computed in such a system.
| |
| | |
| Geocentric coordinate systems used in geodesy can be divided naturally into two classes:
| |
| # [[Inertial]] reference systems, where the coordinate axes retain their orientation relative to the [[fixed star]]s, or equivalently, to the rotation axes of ideal [[gyroscopes]]; the <math>X</math> axis points to the [[vernal equinox]]
| |
| # Co-rotating, also ECEF ("Earth Centred, Earth Fixed"), where the axes are attached to the solid body of the Earth. The <math>X</math> axis lies within the [[Greenwich meridian|Greenwich]] observatory's [[Meridian (geography)|meridian]] plane.
| |
| | |
| 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 ([[day|length-of-day]] variations). A more accurate description also takes [[polar motion]] into account, a phenomenon closely monitored by geodesists.
| |
| | |
| === Coordinate systems in the plane ===
| |
| In [[surveying]] and [[map]]ping, important fields of application of geodesy, two general types of coordinate systems are used in the plane:
| |
| | |
| # Plano-polar, in which points in a plane are defined by a distance <math>s</math> from a specified point along a ray having a specified direction <math>\alpha</math> with respect to a base line or axis;
| |
| # Rectangular, points are defined by distances from two perpendicular axes called <math>x</math> and <math>y</math>. It is geodetic practice—contrary to the mathematical convention—to let the <math>x</math> axis point to the North and the <math>y</math> axis to the East.
| |
| | |
| Rectangular coordinates in the plane can be used intuitively with respect to one's current location, in which case the <math>x</math> axis will point to the local North. More formally, such coordinates can be obtained from three-dimensional coordinates using the artifice of a [[map projection]]. It is ''not'' possible to map the curved surface of the Earth onto a flat map surface without deformation. The compromise most often chosen—called a [[conformal projection]]—preserves angles and length ratios, so that small circles are mapped as small circles and small squares as squares.
| |
| | |
| An example of such a projection is UTM ([[Universal Transverse Mercator]]). Within the map plane, we have rectangular coordinates <math>x</math> and <math>y</math>. In this case the North direction used for reference is the ''map'' North, not the ''local'' North. The difference between the two is called [[Transverse Mercator projection#Convergence|meridian convergence]].
| |
| | |
| It is easy enough to "translate" between polar and rectangular coordinates in the plane: let, as above, direction and distance be <math>\alpha</math> and <math>s</math> respectively, then we have
| |
| | |
| :<math>
| |
| \begin{matrix}
| |
| x &=& s \cos \alpha\\
| |
| y &=& s \sin \alpha
| |
| \end{matrix}
| |
| </math>
| |
| | |
| The reverse transformation is given by:
| |
| | |
| :<math>
| |
| \begin{matrix}
| |
| s &=& \sqrt{x^2 + y^2}\\
| |
| \alpha &=& \arctan{(y/x)}.
| |
| \end{matrix}
| |
| </math>
| |
| | |
| == Heights == | |
| In geodesy, point or terrain ''[[height]]s'' are "above [[sea level]]", an irregular, physically defined surface. Therefore a height should ideally ''not'' be referred to as a coordinate. It is more like a physical quantity, and though it can be tempting to treat height as the vertical coordinate <math>z</math>, in addition to the horizontal coordinates <math>x</math> and <math>y</math>, and though this actually is a good approximation of physical reality in small areas, it quickly becomes invalid for regional considerations. {{Specify|date=December 2006}}
| |
| | |
| Heights come in the following variants:
| |
| | |
| # [[Orthometric height]]s
| |
| # [[Normal height]]s
| |
| # [[Geopotential height]]s
| |
| | |
| Each has its advantages and disadvantages. Both orthometric and normal heights are heights in metres above sea level, whereas geopotential numbers are measures of potential energy (unit: m² s<sup>−2</sup>) and not metric. Orthometric and normal heights differ in the precise way in which mean sea level is conceptually continued under the continental masses. The reference surface for orthometric heights is the [[geoid]], an equipotential surface approximating mean sea level.
| |
| | |
| ''None'' of these heights is in any way related to '''geodetic''' or '''ellipsoidial''' heights, which express the height of a point above the [[reference ellipsoid]]. Satellite positioning receivers typically provide ellipsoidal heights, unless they are fitted with special conversion software based on a model of the [[geoid]].
| |
| | |
| == Geodetic data ==
| |
| Because geodetic point coordinates (and heights) are always obtained in a system that has been constructed itself using real observations, geodesists introduce the concept of a ''geodetic datum'': a physical realization of a coordinate system used for describing point locations. The realization is the result of ''choosing'' conventional coordinate values for one or more ''datum points''.
| |
| | |
| In the case of height datums, it suffices to choose ''one'' datum point: the reference bench mark, typically a tide gauge at the shore. Thus we have vertical datums like the NAP ([[Normaal Amsterdams Peil]]), the North American Vertical Datum 1988 (NAVD88), the [[Kronstadt datum]], the Trieste datum, and so on.
| |
| | |
| In case of plane or spatial coordinates, we typically need several datum points. A regional, ellipsoidal datum like [[ED50]] can be fixed by prescribing the [[undulation of the geoid]] and the deflection of the vertical in ''one'' datum point, in this case the [[Helmert Tower]] in [[Potsdam]]. However, an overdetermined ensemble of datum points can also be used.
| |
| | |
| Changing the coordinates of a point set referring to one datum, so to make them refer to another datum, is called a ''datum transformation''. In the case of vertical datums, this consists of simply adding a constant shift to all height values. In the case of plane or spatial coordinates, datum transformation takes the form of a similarity or ''Helmert transformation'', consisting of a rotation and scaling operation in addition to a simple translation. In the plane, a [[Helmert transformation]] has four parameters; in space, seven.
| |
| | |
| === A note on terminology ===
| |
| | |
| In the abstract, a coordinate system as used in mathematics and geodesy is, e.g., in [[International Organization for Standardization|ISO]] terminology, referred to as a ''coordinate system''. International geodetic organizations like the [[IERS]] (International Earth Rotation and Reference Systems Service) speak of a ''reference system''.
| |
| | |
| When these coordinates are realized by choosing datum points and fixing a geodetic datum, ISO uses the terminology ''coordinate reference system'', while IERS speaks of a ''reference frame''. A datum transformation again is referred to by ISO as a ''coordinate transformation''. (ISO 19111: Spatial referencing by coordinates).
| |
| | |
| == Point positioning ==
| |
| [[File:Geodetic Control Mark.jpg|250px|thumb|right|Geodetic Control Mark (example of a [[deep benchmark]])]]
| |
| | |
| Point positioning is the determination of the coordinates of a point on land, at sea, or in space with respect to a coordinate system. Point position is solved by computation from measurements linking the known positions of terrestrial or extraterrestrial points with the unknown terrestrial position. This may involve transformations between or among astronomical and terrestrial coordinate systems.
| |
| | |
| The known points used for point positioning can be [[triangulation]] points of a higher order network, or [[Global Positioning System|GPS]] satellites.
| |
| | |
| Traditionally, a hierarchy of networks has been built to allow point positioning within a country. Highest in the hierarchy were triangulation networks. These were densified into networks of [[traverse (surveying)|traverse]]s ([[polygons]]), into which local mapping surveying measurements, usually with measuring tape, corner prism and the familiar red and white poles, are tied.
| |
| | |
| Nowadays all but special measurements (e.g., underground or high precision engineering measurements) are performed with [[Global Positioning System|GPS]]. The higher order networks are measured with [[Global Positioning System|static GPS]], using differential measurement to determine vectors between terrestrial points. These vectors are then adjusted in traditional network fashion. A global polyhedron of permanently operating GPS stations under the auspices of the [[IERS]] is used to define a single global, geocentric reference frame which serves as the "zero order" global reference to which national measurements are attached.
| |
| | |
| For [[surveying]] mappings, frequently [[Real Time Kinematic]] GPS is employed, tying in the unknown points with known terrestrial points close by in real time.
| |
| | |
| One purpose of point positioning is the provision of known points for mapping measurements, also known as (horizontal and vertical) control.
| |
| In every country, thousands of such known points exist and are normally documented by the national mapping agencies. Surveyors involved in real estate and insurance will use these to tie their local measurements to.
| |
| | |
| == Geodetic problems ==
| |
| {{Main|Geodesics on an ellipsoid}}
| |
| | |
| In geometric geodesy, two standard problems exist:
| |
| | |
| === First (direct) geodetic problem ===
| |
| | |
| : Given a point (in terms of its coordinates) and the direction ([[azimuth]]) and [[distance]] from that point to a second point, determine (the coordinates of) that second point.
| |
| | |
| === Second (inverse) geodetic problem === | |
| | |
| : Given two points, determine the azimuth and length of the line (straight line, arc or [[geodesic]]) that connects them.
| |
| | |
| In the case of plane geometry (valid for small areas on the Earth's surface) the solutions to both problems reduce to simple [[trigonometry]].
| |
| On the sphere, the solution is significantly more complex, e.g., in the inverse problem the azimuths will differ between the two end points of the connecting [[great circle]], arc, i.e. the geodesic.
| |
| | |
| On the ellipsoid of revolution, geodesics may be written in terms of elliptic integrals, which are usually evaluated in terms of a series expansion; for example, see [[Vincenty's formulae]].
| |
| | |
| In the general case, the solution is called the [[geodesic]] for the surface considered. The [[differential equation]]s for the [[geodesic]] can be solved numerically.
| |
| | |
| == Geodetic observational concepts == | |
| Here we define some basic observational concepts, like angles and coordinates, defined in geodesy (and astronomy as well), mostly from the viewpoint of the local observer.
| |
| | |
| * The ''[[plumbline]]'' or ''vertical'' is the direction of local gravity, or the line that results by following it.
| |
| * The ''[[zenith]]'' is the point on the [[celestial sphere]] where the direction of the gravity vector in a point, extended upwards, intersects it. More correct is to call it a <direction> rather than a point.
| |
| * The ''[[nadir]]'' is the opposite point (or rather, direction), where the direction of gravity extended downward intersects the (invisible) celestial sphere.
| |
| * The celestial ''horizon'' is a plane perpendicular to a point's gravity vector.
| |
| * ''[[Azimuth]]'' is the direction angle within the plane of the horizon, typically counted clockwise from the North (in geodesy and astronomy) or South (in France).
| |
| * ''[[Elevation]]'' is the angular height of an object above the horizon, Alternatively [[zenith distance]], being equal to 90 degrees minus elevation.
| |
| * ''Local topocentric coordinates'' are azimuth (direction angle within the plane of the horizon) and elevation angle (or zenith angle) and distance.
| |
| * The North ''[[celestial pole]]'' is the extension of the Earth's ([[precession|precessing]] and [[nutation|nutating]]) instantaneous spin axis extended Northward to intersect the celestial sphere. (Similarly for the South celestial pole.)
| |
| * The ''celestial equator'' is the intersection of the (instantaneous) Earth equatorial plane with the celestial sphere.
| |
| * A ''[[meridian (geography)|meridian]] plane'' is any plane perpendicular to the celestial equator and containing the celestial poles.
| |
| * The ''local meridian'' is the plane containing the direction to the zenith and the direction to the celestial pole.
| |
| | |
| == Geodetic measurements ==
| |
| [[File:Stephen Merkowitz NASA's Space Geodesy Project.ogv|thumb|350px|Project manager Stephen Merkowitz talks about his work with NASA's Space Geodesy Project, including a brief overview of the four fundamental techniques of space geodesy: GPS, VLBI, SLR, and DORIS.]]
| |
| | |
| The level is used for determining height differences and height reference systems, commonly referred to [[mean sea level]]. The traditional [[spirit level]] produces these practically most useful heights above sea level directly; the more economical use of GPS instruments for height determination requires precise knowledge of the figure of the [[geoid]], as GPS only gives heights above the [[GRS80]] reference ellipsoid. As geoid knowledge accumulates, one may expect use of GPS heighting to spread.
| |
| | |
| The [[theodolite]] is used to measure horizontal and vertical angles to target points. These angles are referred to the local vertical. The [[tacheometer]] additionally determines, electronically or electro-optically, the distance to target, and is highly automated to even robotic in its operations. The method of [[free station position]] is widely used.
| |
| | |
| For local detail surveys, tacheometers are commonly employed although the old-fashioned rectangular technique using angle prism and steel tape is still an inexpensive alternative. Real-time kinematic (RTK) GPS techniques are used as well. Data collected are tagged and recorded digitally for entry into a [[Geographic information system|Geographic Information System]] (GIS) [[database]].
| |
| | |
| Geodetic [[Global Positioning System|GPS]] receivers produce directly three-dimensional coordinates in a [[geocentric]] coordinate frame. 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]]).
| |
| | |
| GPS receivers have almost completely replaced terrestrial instruments for large-scale base network surveys. For Planet-wide geodetic surveys, previously impossible, we can still mention [[Satellite laser ranging|Satellite Laser Ranging]] (SLR) and [[Lunar laser ranging|Lunar Laser Ranging]] (LLR) and [[Very Long Baseline Interferometry]] (VLBI) techniques. All these techniques also serve to monitor Earth rotation irregularities as well as plate tectonic motions.
| |
| | |
| [[Gravity]] is measured using [[gravimeters]]. Basically, there are two kinds of gravimeters. ''Absolute'' gravimeters, which nowadays can also be used in the field, are based directly on measuring the acceleration of free fall (for example, of a reflecting prism in a vacuum tube). They are used for establishing the vertical geospatial control. Most common ''relative'' gravimeters are spring based. They are used in gravity surveys over large areas for establishing the figure of the geoid over these areas. Most accurate relative gravimeters are ''superconducting'' gravimeters, and these are sensitive to one thousandth of one billionth of the Earth surface gravity. Twenty-some superconducting gravimeters are used worldwide for studying Earth [[tide]]s, [[rotation]], interior, and [[ocean]] and atmospheric loading, as well as for verifying the Newtonian constant of [[gravitation]].
| |
| | |
| == Units and measures on the ellipsoid ==
| |
| Geographical [[latitude]] and [[longitude]] are stated in the units degree, minute of arc, and second of arc. They are ''angles'', not metric
| |
| measures, and describe the ''direction'' of the local normal to the [[reference ellipsoid]] of revolution. This is ''approximately'' the same as the direction of the plumbline, i.e., local gravity, which is also the normal to the geoid surface. For this reason, astronomical position determination – measuring the direction of the plumbline by astronomical means – works fairly well provided an ellipsoidal model of the figure of the Earth is used.
| |
| | |
| One geographical mile, defined as one minute of arc on the equator, equals 1,855.32571922 m. One nautical mile is one minute of astronomical latitude. The radius of curvature of the ellipsoid varies with latitude, being the longest at the pole and the shortest at the equator as is the nautical mile.
| |
| | |
| A metre was originally defined as the 10-millionth part of the length of a meridian (the target was not quite reached in actual implementation, so that is off by 200 [[ppm]] in the current definitions). This means that one kilometre is roughly equal to (1/40,000) * 360 * 60 meridional minutes of arc, which equals 0.54 nautical mile, though this is not exact because the two units are defined on different bases (the international nautical mile is defined as exactly 1,852 m, corresponding to a rounding of 1000/0.54 m to four digits).
| |
| | |
| == Temporal change ==
| |
| In geodesy, temporal change can be studied by a variety of techniques. Points on the Earth's surface change their location due to a variety of mechanisms:
| |
| | |
| * Continental plate motion, [[plate tectonics]]
| |
| * Episodic motion of tectonic origin, esp. close to fault lines
| |
| * Periodic effects due to Earth tides
| |
| * [[glaciation|Postglacial]] land uplift due to isostatic adjustment
| |
| * Various anthropogenic movements due to, for instance, [[petroleum]] or water extraction or reservoir construction.
| |
| | |
| The science of studying deformations and motions of the Earth's crust and the solid Earth as a whole is called [[geodynamics]]. Often, study of the Earth's irregular rotation is also included in its definition.
| |
| | |
| Techniques for studying geodynamic phenomena on the global scale include:
| |
| | |
| * satellite positioning by [[Global Positioning System|GPS]] and other such systems,
| |
| * [[Very Long Baseline Interferometry]] (VLBI)
| |
| * satellite and lunar [[laser ranging]]
| |
| * Regionally and locally, precise levelling,
| |
| * precise tacheometers,
| |
| * monitoring of gravity change,
| |
| * [[Interferometric synthetic aperture radar]] (InSAR) using satellite images, etc.
| |
| | |
| == Famous geodesists ==
| |
| | |
| === Mathematical geodesists before 1900 ===
| |
| | |
| <div style="-moz-column-count:3; column-count:3;"> | |
| * [[Pythagoras]] 580–490 BC, [[ancient Greece]]<ref>[http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/TR80003A.HTM DEFENSE MAPPING AGENCY TECHNICAL REPORT 80-003]</ref>
| |
| * [[Eratosthenes]] 276–194 BC, ancient Greece
| |
| * [[Hipparchus]] ca. 190–120 BC, ancient Greece
| |
| * [[Posidonius]] ca. 135–51 BC, ancient Greece
| |
| * [[Claudius Ptolemy]] 83–c.168 AD, [[Roman Empire]] ([[Roman Egypt]])
| |
| * [[Al-Ma'mun]] 786–833, [[Baghdad]] ([[Iraq]]/[[Mesopotamia]])
| |
| * [[Abu Rayhan Biruni]] 973–1048, [[Greater Khorasan|Khorasan]] ([[Persia|Iran]]/[[Samanid Dynasty]])
| |
| * [[Muhammad al-Idrisi]] 1100–1166, ([[Arabia]] & Sicily)
| |
| * [[Regiomontanus]] 1436–1476, ([[Germany]]/[[Austria]])
| |
| * [[Abel Foullon]] 1513–1563 or 1565, ([[France]])
| |
| * [[Pedro Nunes]] 1502–1578 ([[Portugal]])
| |
| * [[Gerardus Mercator|Gerhard Mercator]] 1512–1594 ([[Belgium]] & [[Germany]])
| |
| * [[Willebrord Snellius|Snellius]] (Willebrord Snel van Royen) 1580–1626, [[Leiden]] ([[Netherlands]])
| |
| * [[Christiaan Huygens]] 1629–1695 ([[Netherlands]])
| |
| * [[Pierre Bouguer]] 1698–1758, ([[France]] & [[Peru]])
| |
| * [[Pierre de Maupertuis]] 1698–1759 ([[France]])
| |
| * [[Alexis Clairaut]] 1713–1765 ([[France]])
| |
| * [[Johann Heinrich Lambert]] 1728–1777 ([[France]])
| |
| * [[Roger Joseph Boscovich]] 1711–1787, ([[Rome]]/ [[Berlin]]/ [[Paris]])
| |
| * [[Ino Tadataka]] 1745-1818, ([[Tokyo]])
| |
| * [[Georg von Reichenbach]] 1771–1826, [[Bavaria]] ([[Germany]])
| |
| * [[Pierre-Simon Laplace]] 1749–1827, [[Paris]] ([[France]])
| |
| * [[Adrien-Marie Legendre|Adrien Marie Legendre]] 1752–1833, [[Paris]] ([[France]])
| |
| * [[Johann Georg von Soldner]] 1776–1833, [[Munich]] ([[Germany]])
| |
| * [[George Everest]] 1830–1843 ([[England]] & [[India]])
| |
| * [[Friedrich Wilhelm Bessel]] 1784–1846, [[Königsberg]] ([[Germany]])
| |
| * [[Heinrich Christian Schumacher]] 1780–1850 ([[Germany]] & [[Estonia]])
| |
| * [[Carl Friedrich Gauß]] 1777–1855, Göttingen ([[Germany]])
| |
| * [[Friedrich Georg Wilhelm Struve]] 1793–1864, [[Tartu Observatory|Dorpat]] and [[Pulkovo Observatory|Pulkovo]] ([[Russian Empire]])
| |
| * [[J. H. Pratt]] 1809–1871, [[London]] ([[England]])
| |
| * [[Friedrich H. C. Paschen]] 1804–1873, [[Schwerin]] ([[Germany]])
| |
| * [[Johann Benedikt Listing]] 1808–1882 ([[Germany]])
| |
| * [[Johann Jacob Baeyer]] 1794–1885, [[Berlin]] ([[Germany]])
| |
| * Sir [[George Biddell Airy]] 1801–1892, [[Cambridge]] & [[London]]
| |
| * [[Karl Maximilian von Bauernfeind]] 1818–1894, [[Munich]] ([[Germany]])
| |
| * [[Wilhelm Jordan (geodesist)|Wilhelm Jordan]] 1842–1899, ([[Germany]])
| |
| * [[Hervé Faye]] 1814–1902 ([[France]])
| |
| * [[George Gabriel Stokes]] 1819–1903 ([[England]])
| |
| * [[Henri Poincaré]] 1854–1912, [[Paris]] ([[France]])
| |
| * [[Alexander Ross Clarke]] 1828–1914, [[London]] ([[England]])
| |
| * [[Charles Sanders Peirce]] 1839–1914 ([[United States]])
| |
| * [[Friedrich Robert Helmert]] 1843–1917, [[Potsdam]] ([[Germany]])
| |
| * [[Heinrich Bruns]] 1848–1919, [[Berlin]] ([[Germany]])
| |
| * [[Loránd Eötvös]] 1848–1919 ([[Hungary]])
| |
| </div> | |
| | |
| ===Twentieth century===
| |
| <div style="-moz-column-count:3; column-count:3;"> | |
| * [[John Fillmore Hayford]], 1868–1925, (US)
| |
| * [[Alfred Wegener]], 1880–1930, (Germany and Greenland)
| |
| * [[William Bowie (engineer)|William Bowie]], 1872–1940, (US)
| |
| * [[Friedrich Hopfner]], 1881–1949, [[Vienna]], (Austria)
| |
| * [[Tadeusz Banachiewicz]], 1882–1954, (Poland)
| |
| * [[F.A. Vening Meinesz|Felix Andries Vening-Meinesz]], 1887–1966, (Netherlands)
| |
| * [[Martin Hotine]], 1898–1968, (England)
| |
| * [[Yrjö Väisälä]], 1889–1971, (Finland)
| |
| * [[Veikko Aleksanteri Heiskanen]], 1895–1971, (Finland and US)
| |
| * [[Karl Ramsayer]], 1911–1982, [[Stuttgart]], (Germany)
| |
| * [[Harold Jeffreys]], 1891–1989, [[London]], (England)
| |
| * [[William M. Kaula]], 1926–2000, [[Los Angeles]], (US)
| |
| * [[Mikhail Molodenskii|Mikhail Sergeevich Molodenskii]], 1909–1991, (Russia)
| |
| * [[Hellmut Schmid]], 1914–1998, (Switzerland)
| |
| * [[John A. O'Keefe]], 1916–2000, (US)
| |
| * [[Thaddeus Vincenty]], 1920–2002, (Poland)
| |
| * [[Willem Baarda]], 1917–2005, (Netherlands)
| |
| * [[Irene Fischer|Irene Kaminka Fischer]], 1907–2009, (US)
| |
| * [[Arne Bjerhammar]], 1917–2011, (Sweden)
| |
| * [[Karl-Rudolf Koch]] 1935, [[Bonn]], (Germany)
| |
| * [[Helmut Moritz]], 1933, [[Graz]], (Austria)
| |
| * [[Petr Vaníček]], 1935, [[Fredericton]], (Canada)
| |
| * [[Erik Grafarend]], 1939, [[Stuttgart]], (Germany)
| |
| * [[Rafael Mercado Aced|Rafael Mercado]], (US)
| |
| </div>
| |
| | |
| == International organizations == | |
| | |
| * [[European Petroleum Survey Group|European Petroleum Survey Group (EPSG)]] (which despite being officially disbanded in 2005 continues to refine a well tested set of [[Geodetic system|Geodetic Parameters]])
| |
| * [[International Federation of Surveyors]] (FIG)
| |
| * [[International Geodetic Student Organisation|International Geodetic Student Organisation (IGSO)]]
| |
| | |
| == Governmental agencies ==
| |
| {{globalize|section|date=October 2013}}
| |
| *[[U.S. National Geodetic Survey|NGS]], Silver Spring MD, USA
| |
| *[[National Geospatial-Intelligence Agency|NGA]], Bethesda MD, USA (Previously National Imagery and Mapping Agency NIMA, previously Defense Mapping Agency DMA)
| |
| * ([[USGS]]), Reston VA, USA
| |
| | |
| == See also == | |
| ;Fundamentals: [[Geodynamics]]{{·}}[[Geomatics]]{{·}}[[Cartography]]{{·}}[[Geodesics on an ellipsoid]]{{·}}[[Physical geodesy]]
| |
| | |
| ;Concepts: [[Datum (geodesy)|Datum]]{{·}}[[Geographical distance|Distance]]{{·}}[[Figure of the Earth]]{{·}}[[Geoid]]{{·}}[[Geodetic system]]{{·}}[[Geographic coordinate system|Geog. coord. system]]{{·}}[[Horizontal position representation]]{{·}}[[Map projection]]{{·}}[[Reference ellipsoid]]{{·}}[[Satellite geodesy]]{{·}}[[Spatial reference system]] <!-- others: -->
| |
| | |
| ;Geodesy community: [[List of publications in geology#Geodetics|Important publications in geodesy]]{{·}}[[International Association of Geodesy|International Association of Geodesy (IAG)]]
| |
| | |
| ;Technologies: [[Satellite navigation|GNSS]]{{·}}[[Global Positioning System|GPS]]{{·}}[[Space techniques]]
| |
| | |
| ;Standards: [[ED50]]{{·}}[[European Terrestrial Reference System 1989|ETRS89]]{{·}}[[North American Datum#North American Datum of 1983|NAD83]]{{·}}[[North American Vertical Datum of 1988|NAVD88]]{{·}}[[South American Datum#SAD69|SAD69]]{{·}}[[SRID]]{{·}}[[Universal Transverse Mercator coordinate system|UTM]]{{·}}[[World Geodetic System|WGS84]]
| |
| | |
| ;History: [[History of geodesy]]{{·}}[[Sea Level Datum of 1929|NAVD29]]
| |
| | |
| ;Other: [[Geodesic (general relativity)]]{{·}}[[Surveying]]{{·}}[[Meridian arc]]{{·}}[[Lenart Sphere]]
| |
| | |
| == Notes ==
| |
| {{reflist}}
| |
| | |
| == References ==
| |
| * F. R. Helmert, [http://geographiclib.sf.net/geodesic-papers/helmert80-en.html ''Mathematical and Physical Theories of Higher Geodesy'', Part 1], ACIC (St. Louis, 1964). This is an English translation of ''Die mathematischen und physikalischen Theorieen der höheren Geodäsie'', Vol 1 (Teubner, Leipzig, 1880).
| |
| * F. R. Helmert, [http://geographiclib.sf.net/geodesic-papers/helmert84-en.html ''Mathematical and Physical Theories of Higher Geodesy'', Part 2], ACIC (St. Louis, 1964). This is an English translation of ''Die mathematischen und physikalischen Theorieen der höheren Geodäsie'', Vol 2 (Teubner, Leipzig, 1884).
| |
| * B. Hofmann-Wellenhof and H. Moritz, ''Physical Geodesy'', Springer-Verlag Wien, 2005. (This text is an updated edition of the 1967 classic by W.A. Heiskanen and H. Moritz).
| |
| * W. Kaula, ''Theory of Satellite Geodesy : Applications of Satellites to Geodesy'', Dover Publications, 2000. (This text is a reprint of the 1966 classic).
| |
| * Vaníček P. and E.J. Krakiwsky, ''Geodesy: the Concepts'', pp. 714, Elsevier, 1986.
| |
| * Torge, W (2001), ''Geodesy'' (3rd edition), published by de Gruyter, isbn=3-11-017072-8.
| |
| * Thomas H. Meyer, Daniel R. Roman, and David B. Zilkoski. "What does ''height'' really mean?" (This is a series of four articles published in ''Surveying and Land Information Science, SaLIS''.)
| |
| ** [http://digitalcommons.uconn.edu/thmeyer_articles/2 "Part I: Introduction"] ''SaLIS'' Vol. 64, No. 4, pages 223–233, December 2004.
| |
| ** [http://digitalcommons.uconn.edu/thmeyer_articles/3 "Part II: Physics and gravity"] ''SaLIS'' Vol. 65, No. 1, pages 5–15, March 2005.
| |
| ** [http://digitalcommons.uconn.edu/nrme_articles/2 "Part III: Height systems"] ''SaLIS'' Vol. 66, No. 2, pages 149–160, June 2006.
| |
| ** [http://digitalcommons.uconn.edu/nrme_articles/5 "Part IV: GPS heighting"] ''SaLIS'' Vol. 66, No. 3, pages 165–183, September 2006.
| |
| | |
| ==External links== | |
| {{Wikibooks}}
| |
| {{commons category|Geodesy}}
| |
| | |
| {{Earth science}}
| |
| {{Geophysics navbox}}
| |
| | |
| [[Category:Geodesy| ]]
| |
| [[Category:Cartography]]
| |
| [[Category:Geophysics]]
| |
| [[Category:Measurement]]
| |