1.
National Grid (Great Britain)
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The UK grid is connected as a wide area synchronous grid nominally running at 50 hertz. There are also undersea interconnections to northern France, Northern Ireland, the Isle of Man, the Netherlands, in Scotland the grid split into two separate entities, one for southern and central Scotland and the other for northern Scotland, connected by interconnectors to each other. The first is owned and maintained by SP Energy Networks, a subsidiary of Scottish Power, however, National Grid plc remains the System Operator for the whole UK Grid. At the end of the 19th century, Nikola Tesla established the principles of three-phase high-voltage electric power distribution while he was working for Westinghouse in the United States. The first to use this system in the United Kingdom was Charles Merz, of the Merz & McLellan consulting partnership and this opened in 1901, and by 1912 had developed into the largest integrated power system in Europe. The rest of the country, however, continued to use a patchwork of small supply networks, in 1925, the British government asked Lord Weir, a Glaswegian industrialist, to solve the problem of Britains inefficient and fragmented electricity supply industry. Weir consulted Merz, and the result was the Electricity Act 1926, the 1926 Act created the Central Electricity Board, which set up the UKs first synchronised, nationwide AC grid, running at 132 kV,50 Hz. The grid was created with 4,000 miles of cables- mostly overhead cables, linking the 122 most efficient power stations and it began operating in 1933 as a series of regional grids with auxiliary interconnections for emergency use. Following the unauthorised but successful short term parallelling of all regional grids by the engineers on 29 October 1937. The growth by then in the number of electricity users was the fastest in the world and it proved its worth during the Blitz when South Wales provided power to replace lost output from Battersea and Fulham power stations. The grid was nationalised by the Electricity Act 1947, which created the British Electricity Authority. In 1949, the British Electricity Authority decided to upgrade the grid by adding 275 kV links. The 275 kV Transmission System at the time of its inception in 1950, was designed to part of a national supply system with an anticipated total demand of 30,000 MW by 1970. The predicted demand was already exceeded by 1960, the rapid load growth led the Central Electricity Generating Board to carry out a study in 1960 of future transmission needs. The report was completed in September 1960, and its study is described in a paper presented to the Institution of Electrical Engineers by Messrs E. S, booth, D. Clark, J. L. Egginton and J. S. Forrest in 1962. West Burton with 4 x 500 MW machines, sited at the Nottinghamshire coalfield near the River Trent, is a typical example, continued reinforcement and extension of the existing 275 kV systems was examined as a possible solution. However, in addition to the problem of very high fault levels many more lines would have been required to obtain the estimated transfers at 275 kV. As this was not consistent with the Central Electricity Generating Boards policy of preservation of amenities a further solution was sought, consideration was given to both a 400 kV and 500 kV scheme as the alternatives, either of which gave a sufficient margin for future expansion
2.
Geodesy
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Geodesists also study geodynamical phenomena such as crustal motion, tides, and polar motion. For this they design global and national networks, using space and terrestrial techniques while relying on datums. Geodesy — from the Ancient Greek word γεωδαισία geodaisia — is primarily concerned with positioning within the temporally varying gravity field, such geodetic operations are also applied to other astronomical bodies in the solar system. It is also the science of measuring and understanding the earths geometric shape, orientation in space and this applies to the solid surface, the liquid surface and the Earths atmosphere. For this reason, the study of the Earths gravity field is called physical geodesy by some, the geoid is essentially the figure of the Earth abstracted from its topographical features. It is an idealized surface of sea water, the mean sea level surface in the absence of currents, air pressure variations etc. The geoid, unlike the 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 ellipsoid is called the geoidal undulation. It varies globally between ±110 m, when referred to the GRS80 ellipsoid, a reference ellipsoid, customarily chosen to be the same size as the geoid, is described by its semi-major axis a and flattening f. The quantity f = a − b/a, where b is the axis, is a purely geometrical one. The mechanical ellipticity of the Earth can be determined to high precision by observation of satellite orbit perturbations and its relationship with the geometrical flattening is indirect. The relationship depends on the density distribution, or, in simplest terms. The 1980 Geodetic Reference System posited a 6,378,137 m semi-major axis and this system was adopted at the XVII General Assembly of the International Union of Geodesy and Geophysics. It is essentially the basis for geodetic positioning by the Global Positioning System and is also in widespread use outside the geodetic community. The locations of points in space are most conveniently described by three cartesian or rectangular coordinates, X, Y and Z. Since the advent of satellite positioning, such systems are typically geocentric. The X-axis lies within the Greenwich observatorys meridian plane, the coordinate transformation between these two systems is described to good approximation by sidereal time, which takes into account variations in the Earths axial rotation. A more accurate description also takes polar motion into account, a closely monitored by geodesists
3.
Geodynamics
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Geodynamics is a subfield of geophysics dealing with dynamics of the Earth. It also attempts to probe the internal activity by measuring magnetic fields, gravity, methods of geodynamics are also applied to exploration of other planets. Geodynamics is generally concerned with processes that move throughout the Earth. In the Earth’s interior, movement happens when rocks melt or deform and this deformation may be brittle, elastic, or plastic, depending on the magnitude of the stress and the material’s physical properties, especially the stress relaxation time scale. Rocks are structurally and compositionally heterogeneous and are subjected to variable stresses, when working with geological timescales and lengths, it is convenient to use the continuous medium approximation and equilibrium stress fields to consider the average response to average stress. Experts in geodynamics commonly use data from geodetic GPS, InSAR, rocks and other geological materials experience strain according three distinct modes, elastic, plastic, and brittle depending on the properties of the material and the magnitude of the stress field. Stress is defined as the force per unit area exerted on each part of the rock. Pressure is the part of stress changes the volume of a solid. If there is no shear, the fluid is in hydrostatic equilibrium, since, over long periods, rocks readily deform under pressure, the Earth is in hydrostatic equilibrium to a good approximation. The pressure on rock depends only on the weight of the rock above, and this depends on gravity, in a body like the Moon, the density is almost constant, so a pressure profile is readily calculated. In the Earth, the compression of rocks with depth is significant, elastic deformation is always reversible, which means that if the stress field associated with elastic deformation is removed, the material will return to its previous state. Materials only behave elastically when the arrangement along the axis being considered of material components remains unchanged. This means that the magnitude of the stress cannot exceed the strength of a material. If stress exceeds the strength of a material, bonds begin to break. During ductile deformation, this process of atomic rearrangement redistributes stress, examples include bending of the lithosphere under volcanic islands or sedimentary basins, and bending at oceanic trenches. Ductile deformation happens when transport processes such as diffusion and advection that rely on chemical bonds to be broken, when strain localizes faster than these relaxation processes can redistribute it, brittle deformation occurs. In other words, any fracture, however small, tends to focus strain at its leading edge, in general, the mode of deformation is controlled not only by the amount of stress, but also by the distribution of strain and strain associated features. Structural geologists study the results of deformation, using observations of rock, especially the mode, structural geology is an important complement to geodynamics because it provides the most direct source of data about the movements of the Earth
4.
Geomatics
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Geomatics, also known as surveying engineering or geospatial science, is the discipline of gathering, storing, processing, and delivering geographic information or spatially referenced information. In other words, it consists of products, services and tools involved in the collection, integration, the related field of hydrogeomatics covers the area associated with surveying work carried out on, above or below the surface of the sea or other areas of water. The older term of hydrographics was considered too specific to the preparation of marine charts, a geospatial network is a network of collaborating resources for sharing and coordinating geographical data and data tied to geographical references. One example of such a network is the Open Geospatial Consortiums efforts to provide global access to geographic information. A number of university departments which were once titled surveying, survey engineering or topographic science have re-titled themselves using the terms geomatics or geomatic engineering. The science of deriving information about an object using a sensor without physically contacting it is called remote sensing, Geospatial science is an academic discipline incorporating fields such as surveying, geographic information systems, hydrography and cartography. Spatial science is concerned with the measurement, management, analysis and display of spatial information describing the Earth, its physical features. The term spatial science or spatial sciences is primarily used in Australia, australian universities which offer degrees in spatial science include Curtin University, the University of Tasmania, the University of Adelaide, Melbourne University and RMIT University. Texas A&M University offers a degree in Spatial Sciences and is home to its own Spatial Sciences Laboratory. In place, the university now offers graduate programs strictly related to spatial science, Spatial information practitioners within the Asia-Pacific region are represented by the professional body called the Surveying and Spatial Sciences Institute. Geomatics Engineering, Geomatic Engineering, Geospatial Engineering is a rapidly developing engineering discipline that focuses on spatial information, the location is the primary factor used to integrate a very wide range of data for spatial analysis and visualization. Like how the profession of mechanics is a part of engineering, surveying is a part of geomatic engineering. Therefore, the engineer can be involved in an extremely wide variety of information gathering activities. Geomatics engineers design, develop, and operate systems for collecting and analyzing spatial information about the land, the oceans, natural resources, and manmade features. The tasks more closely related to civil engineering include the design and layout of public infrastructure and urban subdivisions, Geomatics engineers serve society by collecting, monitoring, archiving, and maintaining diverse spatial data infrastructures. These tools enable the geomatics engineer to gather, process, analyze, visualize, Geomatics engineering is the field of activity that integrates the acquisition, processing, analysis, display and management of spatial information. These facts demonstrate the breadth, depth and scope of the highly interdisciplinary nature of geomatics engineering, the job of geospatial engineer is well established in the U. S. military. Geomatic Methods for the Analysis of Data in the Earth Sciences, yvan Bédard, Geomatics in Karen Kemp, Encyclopedia of Geographic Information Science, Sage
5.
Cartography
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Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively, the fundamental problems of traditional cartography are to, Set the maps agenda and select traits of the object to be mapped. This is the concern of map editing, traits may be physical, such as roads or land masses, or may be abstract, such as toponyms or political boundaries. Represent the terrain of the object on flat media. This is the concern of map projections, eliminate characteristics of the mapped object that are not relevant to the maps purpose. This is the concern of generalization, reduce the complexity of the characteristics that will be mapped. This is also the concern of generalization, orchestrate the elements of the map to best convey its message to its audience. This is the concern of map design, modern cartography constitutes many theoretical and practical foundations of geographic information systems. The earliest known map is a matter of debate, both because the term map isnt well-defined and because some artifacts that might be maps might actually be something else. A wall painting that might depict the ancient Anatolian city of Çatalhöyük has been dated to the late 7th millennium BCE, the oldest surviving world maps are from 9th century BCE Babylonia. One shows Babylon on the Euphrates, surrounded by Assyria, Urartu and several cities, all, in turn, another depicts Babylon as being north of the world center. The ancient Greeks and Romans created maps since Anaximander in the 6th century BCE, in the 2nd century AD, Ptolemy wrote his treatise on cartography, Geographia. This contained Ptolemys world map – the world known to Western society. As early as the 8th century, Arab scholars were translating the works of the Greek geographers into Arabic, in ancient China, geographical literature dates to the 5th century BCE. The oldest extant Chinese maps come from the State of Qin, dated back to the 4th century BCE, in the book of the Xin Yi Xiang Fa Yao, published in 1092 by the Chinese scientist Su Song, a star map on the equidistant cylindrical projection. Early forms of cartography of India included depictions of the pole star and these charts may have been used for navigation. Mappa mundi are the Medieval European maps of the world, approximately 1,100 mappae mundi are known to have survived from the Middle Ages. Of these, some 900 are found illustrating manuscripts and the remainder exist as stand-alone documents, the Arab geographer Muhammad al-Idrisi produced his medieval atlas Tabula Rogeriana in 1154
6.
History of geodesy
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Geodesy, also named geodetics, is the scientific discipline that deals with the measurement and representation of the Earth. The history of geodesy began in antiquity and blossomed during the Age of Enlightenment, early ideas about the figure of the Earth held the Earth to be flat, and the heavens a physical dome spanning over it. The early Greeks, in their speculation and theorizing, ranged from the flat disc advocated by Homer to the spherical body postulated by Pythagoras, pythagorass idea was supported later by Aristotle. Pythagoras was a mathematician and to him the most perfect figure was a sphere and he reasoned that the gods would create a perfect figure and therefore the Earth was created to be spherical in shape. Anaximenes, an early Greek philosopher, believed strongly that the Earth was rectangular in shape, since the spherical shape was the most widely supported during the Greek Era, efforts to determine its size followed. Platos figure was a guess and Archimedes a more conservative approximation, in Egypt, a Greek scholar and philosopher, Eratosthenes, is said to have made more explicit measurements. He had heard that on the longest day of the summer solstice, at the same time, he observed the sun was not directly overhead at Alexandria, instead, it cast a shadow with the vertical equal to 1/50th of a circle. Legend has it that he had someone walk from Alexandria to Syene to measure the distance, the circumference of the Earth is 24,902 mi. Over the poles it is more precisely 40,008 km or 24,860 mi, the actual unit of measure used by Eratosthenes was the stadion. No one knows for sure what his stadion equals in modern units, had the experiment been carried out as described, it would not be remarkable if it agreed with actuality. What is remarkable is that the result was only about 0. 4% too high. A parallel later ancient measurement of the size of the Earth was made by another Greek scholar and he is said to have noted that the star Canopus was hidden from view in most parts of Greece but that it just grazed the horizon at Rhodes. Posidonius is supposed to have measured the elevation of Canopus at Alexandria and he assumed the distance from Alexandria to Rhodes to be 5000 stadia, and so he computed the Earths circumference in stadia as 48 times 5000 =240,000. Some scholars see these results as luckily semi-accurate due to cancellation of errors, the abovementioned larger and smaller sizes of the Earth were those used by Claudius Ptolemy at different times,252,000 stadia in his Almagest and 180,000 stadia in his later Geography. The Indian mathematician Aryabhata was a pioneer of mathematical astronomy and he describes the earth as being spherical and that it rotates on its axis, among other things in his work Āryabhaṭīya. Aryabhatiya is divided into four sections, the discovery that the earth rotates on its own axis from west to east is described in Aryabhatiya. Aryabhata gives the radii of the orbits of the planets in terms of the Earth-Sun distance as essentially their periods of rotation around the Sun and he also gave the correct explanation of lunar and solar eclipses and that the Moon shines by reflecting sunlight. The Muslim scholars, who held to the spherical Earth theory, used it to calculate the distance and this determined the Qibla, or Muslim direction of prayer
7.
Geographical distance
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Geographical distance is the distance measured along the surface of the earth. The formulae in this article calculate distances between points which are defined by geographical coordinates in terms of latitude and longitude and this distance is an element in solving the second geodetic problem. Common abstractions for the surface between two points are, Flat surface, Spherical surface, Ellipsoidal surface. All abstractions above ignore changes in elevation, calculation of distances which account for changes in elevation relative to the idealized surface are not discussed in this article. Distance, D, is calculated between two points, P1 and P2, the geographical coordinates of the two points, as pairs, are and, respectively. Which of the two points is designated as P1 is not important for the calculation of distance, latitude and longitude coordinates on maps are usually expressed in degrees. In the given forms of the formulae below, one or more values must be expressed in the units to obtain the correct result. Many electronic calculators allow calculations of trigonometric functions in either degrees or radians, the calculator mode must be compatible with the units used for geometric coordinates. Differences in latitude and longitude are labeled and calculated as follows and it is not important whether the result is positive or negative when used in the formulae below. Mean latitude is labeled and calculated as follows, ϕ m = ϕ1 + ϕ22. Colatitude is labeled and calculated as follows, For latitudes expressed in radians, θ = π2 − ϕ, For latitudes expressed in degrees, θ =90 ∘ − ϕ. Unless specified otherwise, the radius of the earth for the calculations below is, D = Distance between the two points, as measured along the surface of the earth and in the same units as the value used for radius unless specified otherwise. Longitude has singularities at the Poles and a discontinuity at the ±180° meridian, also, planar projections of the circles of constant latitude are highly curved near the Poles. Hence, the equations for delta latitude/longitude and mean latitude may not give the expected answer for positions near the Poles or the ±180° meridian. Consider e. g. the value of Δ λ when λ1 and λ2 are on side of the ±180° meridian. If a calculation based on latitude/longitude should be valid for all Earth positions, it should be verified that the discontinuity, another solution is to use n-vector instead of latitude/longitude, since this representation does not have discontinuities or singularities. A planar approximation for the surface of the earth may be useful over small distances, the accuracy of distance calculations using this approximation become increasingly inaccurate as, The separation between the points becomes greater, A point becomes closer to a geographic pole. The shortest distance between two points in plane is a straight line, the Pythagorean theorem is used to calculate the distance between points in a plane
8.
Geoid
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The geoid is the shape that the surface of the oceans would take under the influence of Earths gravity and rotation alone, in the absence of other influences such as winds and tides. This surface is extended through the continents, all points on a geoid surface have the same gravity potential energy. The geoid can be defined at any value of gravitational potential such as within the earths crust or far out in space and it does not correspond to the actual surface of Earths crust, but to a surface which can only be known through extensive gravitational measurements and calculations. It is often described as the true figure of the Earth. The surface of the geoid is higher than the reference ellipsoid wherever there is a gravity anomaly. The geoid surface is irregular, unlike the ellipsoid which is a mathematical idealized representation of the physical Earth. Although the physical Earth has excursions of +8,848 m and −429 m, If the ocean surface were isopycnic and undisturbed by tides, currents, or weather, it would closely approximate the geoid. The permanent deviation between the geoid and mean sea level is called ocean surface topography, If the continental land masses were criss-crossed by a series of tunnels or canals, the sea level in these canals would also very nearly coincide with the geoid. This means that when traveling by ship, one does not notice the undulations of the geoid, the vertical is always perpendicular to the geoid. Likewise, spirit levels will always be parallel to the geoid, a long voyage, indicate height variations, even though the ship will always be at sea level. This is because GPS satellites, orbiting about the center of gravity of the Earth, to obtain ones geoidal height, a raw GPS reading must be corrected. Conversely, height determined by spirit leveling from a tidal measurement station, as in land surveying. Modern GPS receivers have a grid implemented inside where they obtain the height over the World Geodetic System ellipsoid from the current position. Then they are able to correct the height above WGS ellipsoid to the height above WGS84 geoid, in that case when the height is not zero on a ship it is due to various other factors such as ocean tides, atmospheric pressure and local sea surface topography. The gravitational field of the earth is neither perfect n If that perfect sphere were then covered in water, instead, the water level would be higher or lower depending on the particular strength of gravity in that location. Spherical harmonics are used to approximate the shape of the geoid. The current best such set of spherical harmonic coefficients is EGM96, the geoid is a particular equipotential surface, and is somewhat involved to compute. The gradient of this also provides a model of the gravitational acceleration
9.
Figure of the Earth
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The expression figure of the Earth has various meanings in geodesy according to the way it is used and the precision with which the Earths size and shape is to be defined. The actual topographic surface is most apparent with its variety of land forms and this is, in fact, the surface on which actual Earth measurements are made. The topographic surface is generally the concern of topographers and hydrographers, the Pythagorean concept of a spherical Earth offers a simple surface that is mathematically easy to deal with. Many astronomical and navigational computations use it as a representing the Earth. The idea of a planar or flat surface for Earth, however, is sufficient for surveys of small areas, as the local topography is far more significant than the curvature. Plane-table surveys are made for small areas, and no account is taken of the curvature of the Earth. A survey of a city would likely be computed as though the Earth were a surface the size of the city. For such small areas, exact positions can be determined relative to each other without considering the size, in the mid- to late 20th century, research across the geosciences contributed to drastic improvements in the accuracy of the figure of the Earth. The primary utility of this improved accuracy was to provide geographical and gravitational data for the guidance systems of ballistic missiles. This funding also drove the expansion of geoscientific disciplines, fostering the creation, the models for the figure of the Earth vary in the way they are used, in their complexity, and in the accuracy with which they represent the size and shape of the Earth. The simplest model for the shape of the entire Earth is a sphere, the Earths radius is the distance from Earths center to its surface, about 6,371 kilometers. The concept of a spherical Earth dates back to around the 6th century BC, the first scientific estimation of the radius of the earth was given by Eratosthenes about 240 BC, with estimates of the accuracy of Eratosthenes’s measurement ranging from 2% to 15%. The Earth is only approximately spherical, so no single value serves as its natural radius, distances from points on the surface to the center range from 6,353 km to 6,384 km. Several different ways of modeling the Earth as a sphere each yield a mean radius of 6,371 kilometers, regardless of the model, any radius falls between the polar minimum of about 6,357 km and the equatorial maximum of about 6,378 km. The difference 21 kilometers correspond to the polar radius being approximately 0. 3% shorter than the equator radius, since the Earth is flattened at the poles and bulges at the equator, geodesy represents the shape of the earth with an oblate spheroid. The oblate spheroid, or oblate ellipsoid, is an ellipsoid of revolution obtained by rotating an ellipse about its shorter axis and it is the regular geometric shape that most nearly approximates the shape of the Earth. A spheroid describing the figure of the Earth or other body is called a reference ellipsoid. The reference ellipsoid for Earth is called an Earth ellipsoid, an ellipsoid of revolution is uniquely defined by two numbers, two dimensions, or one dimension and a number representing the difference between the two dimensions
10.
Geodetic datum
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A geodetic datum or geodetic system is a coordinate system, and a set of reference points, used to locate places on the Earth. An approximate definition of sea level is the datum WGS84, other datums are defined for other areas or at other times, ED50 was defined in 1950 over Europe and differs from WGS84 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. Datums are used in geodesy, navigation, and surveying by cartographers, each starts with an ellipsoid, and then defines latitude, longitude and altitude coordinates. One or more locations on the Earths surface are chosen as anchor base-points, the difference in co-ordinates between datums is commonly referred to as datum shift. The datum shift between two particular datums can vary from one place to another within one country or region, the North Pole, South Pole and Equator will be in different positions on different datums, so True North will be slightly different. Different datums use different interpolations for the shape and size of the Earth. Because the Earth is an ellipsoid, localised datums can give a more accurate representation of the area of coverage than WGS84. OSGB36, for example, is an approximation to the geoid covering the British Isles than the global WGS84 ellipsoid. However, as the benefits of a global system outweigh the greater accuracy, horizontal datums are used for describing a point on the Earths surface, in latitude and longitude or another coordinate system. Vertical datums measure elevations or depths, in surveying and geodesy, a datum is a reference system or an approximation of the Earths surface against which positional measurements are made for computing locations. Horizontal datums are used for describing a point on the Earths surface, vertical datums are used to measure elevations or underwater depths. The horizontal datum is the used to measure positions on the Earth. A specific point on the Earth can have different coordinates. There are hundreds of local horizontal datums around the world, usually referenced to some convenient local reference point, contemporary datums, based on increasingly accurate measurements of the shape of the Earth, are intended to cover larger areas. The WGS84 datum, which is almost identical to the NAD83 datum used in North America, a vertical datum is used as a reference point for elevations of surfaces and features on the Earth including terrain, bathymetry, water levels, and man-made structures. Vertical datums are either, tidal, based on sea levels, gravimetric, based on a geoid, or geodetic, for the purpose of measuring the height of objects on land, the usual datum used is mean sea level. This is a datum which is described as the arithmetic mean of the hourly water elevation taken over a specific 19 years cycle