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Geodesy

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.

History
Geodesy began in pre-scientific antiquity, so the very word geodesy comes from the Ancient Greek word γεωδαισία or geodaisia (literally, "division of Earth").

Early ideas about the figure of the Earth held the Earth to be flat and the heavens a physical dome spanning over it. Two early arguments for a spherical Earth were that lunar eclipses appear to an observer as circular shadows and that Polaris appears lower and lower in the sky to a traveler headed South.

Definition
In English, geodesy refers to the science of measuring and representing geospatial information, while geomatics encompasses practical applications of geodesy on local and regional scales, including surveying.

In German, geodesy can refer to either higher geodesy (höhere Geodäsie or Erdmessung, literally "geomensuration") — concerned with measuring Earth on the global scale, or engineering geodesy (Ingenieurgeodäsie) that includes surveying — measuring parts or regions of Earth.

For the longest time, geodesy was the science of measuring and understanding Earth's geometric shape, orientation in space, and gravitational field; however, geodetic science and operations are applied to other astronomical bodies in our Solar System also.

To a large extent, Earth's shape is the result of rotation, which causes its equatorial bulge, and the competition of geological processes such as the collision of plates, as well as of volcanism, resisted by Earth's gravitational field. This applies to the solid surface, the liquid surface (dynamic sea surface topography), and Earth's atmosphere. For this reason, the study of Earth's gravitational field is called physical geodesy.

Geoid and reference ellipsoid

The geoid essentially is the figure of Earth abstracted from its topographical features. It is an idealized equilibrium surface of seawater, the mean sea level surface in the absence of currents and air pressure variations, and continued under the continental masses. Unlike a reference ellipsoid, the geoid is irregular and too complicated to serve as the computational surface for solving geometrical problems like point positioning. The geometrical separation between the geoid and a reference ellipsoid is called geoidal undulation, and it varies globally between ±110 m based on 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 = $a$, where b is the semi-minor axis (polar radius), is purely geometrical. The mechanical ellipticity of Earth (dynamical flattening, symbol J2) can be determined to high precision by observation of satellite orbit perturbations. Its relationship with geometrical flattening is indirect and depends on the internal density distribution or, in simplest terms, the degree of central concentration of mass.

The 1980 Geodetic Reference System (GRS 80), adopted at the XVII General Assembly of the International Union of Geodesy and Geophysics (IUGG), posited a 6,378,137 m semi-major axis and a 1:298.257 flattening. GRS 80 essentially constitutes the basis for geodetic positioning by the Global Positioning System (GPS) and is thus also in widespread use outside the geodetic community. Numerous systems used for mapping and charting are becoming obsolete as countries increasingly move to global, geocentric reference systems utilizing the GRS 80 reference ellipsoid.

The geoid is a "realizable" surface, meaning it can be consistently located on Earth by suitable simple measurements from physical objects like a tide gauge. The geoid can, therefore, be considered a physical ("real") surface. The reference ellipsoid, however, has many possible instantiations and is not readily realizable, so it is an abstract surface. The third primary surface of geodetic interest — the topographic surface of Earth — is also realizable.

Coordinate systems in space

The locations of points in 3D space most conveniently are described by three cartesian or rectangular coordinates, X, Y, and Z. Since the advent of satellite positioning, such coordinate systems are typically geocentric, with the Z-axis aligned to Earth's (conventional or instantaneous) rotation axis.

Before the era of satellite geodesy, the coordinate systems associated with a geodetic datum attempted to be geocentric, but with the origin differing from the geocenter by hundreds of meters due to regional deviations in the direction of the plumbline (vertical). These regional geodetic datums, 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.

It is only because GPS satellites orbit about the geocenter that this point becomes naturally the origin of a coordinate system defined by satellite geodetic means, as the satellite positions in space themselves get computed within such a system.

Geocentric coordinate systems used in geodesy can be divided naturally into two classes:
 * 1) The inertial reference systems, where the coordinate axes retain their orientation relative to the fixed stars or, equivalently, to the rotation axes of ideal gyroscopes; the X-axis points to the vernal equinox
 * 2) The co-rotating reference systems (also ECEF or "Earth Centred, Earth Fixed"), in which the axes are "attached" to the solid body of Earth. The X-axis lies within the Greenwich observatory's meridian plane.

The coordinate transformation between these two systems to good approximation is described by (apparent) sidereal time, which accounts for variations in Earth's axial rotation (length-of-day variations). A more accurate description also accounts for polar motion as a phenomenon closely monitored by geodesists.

Coordinate systems in the plane

In geodetic applications like surveying and mapping, two general types of coordinate systems in the plane are in use:

 * 1) Plano-polar, with points in the plane defined by their distance, s, from a specified point along a ray having a direction α from a baseline or axis;
 * 2) Rectangular, with points defined by distances from two mutually perpendicular axes, x and y. Contrary to the mathematical convention, in geodetic practice, the x-axis points North and the y-axis East.

One can intuitively use rectangular coordinates in the plane for one's current location, in which case the x-axis will point to the local north. More formally, such coordinates can be obtained from 3D coordinates using the artifice of a map projection. It is impossible to map the curved surface of 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 get 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 x and y. In this case, the north direction used for reference is the map north, not the local north. The difference between the two is called meridian convergence.

It is easy enough to "translate" between polar and rectangular coordinates in the plane: let, as above, direction and distance be α and s respectively, then we have

 * $$\begin{align}

x &= s \cos \alpha\\ y &= s \sin \alpha \end{align}$$

The reverse transformation is given by:

 * $$\begin{align}

s &= \sqrt{x^2 + y^2}\\ \alpha &= \arctan\frac{y}{x}. \end{align}$$

Heights

In geodesy, point or terrain heights are "above sea level" as an irregular, physically defined surface. Height systems in use are:

 * 1) Orthometric heights
 * 2) Dynamic heights
 * 3) Geopotential heights
 * 4) Normal heights

Each system has its advantages and disadvantages. Both orthometric and normal heights are expressed in metres above sea level, whereas geopotential numbers are measures of potential energy (unit: m2 s−2) and not metric. The reference surface is the geoid, an equigeopotential surface approximating the mean sea level as described above. For normal heights, the reference surface is the so-called quasi-geoid, which has a few-metre separation from the geoid due to the density assumption in its continuation under the continental masses.

One can relate these heights through the geoid undulation concept to ellipsoidal heights (also known as geodetic heights), representing the height of a point above the reference ellipsoid. Satellite positioning receivers typically provide ellipsoidal heights unless fitted with special conversion software based on a model of the geoid.

Geodetic datums
Because coordinates and heights of geodetic points always get obtained within a system that itself was constructed based on real-world observations, geodesists introduced the concept of a "geodetic datum" (plural datums): a physical (real-world) realization of a coordinate system used for describing point locations. This realization follows from choosing (therefore conventional) coordinate values for one or more datum points. In the case of height data, it suffices to choose one datum point — the reference benchmark, typically a tide gauge at the shore. Thus we have vertical datums, such as the NAVD 88 (North American Vertical Datum 1988), NAP (Normaal Amsterdams Peil), the Kronstadt datum, the Trieste datum, and numerous others.

In both mathematics and geodesy, a coordinate system is a "coordinate system" per ISO terminology, whereas the International Earth Rotation and Reference Systems Service (IERS) uses the term "reference system" for the same. When coordinates are realized by choosing datum points and fixing a geodetic datum, ISO speaks of a "coordinate reference system", whereas IERS uses a "reference frame" for the same. The ISO term for a datum transformation again is a "coordinate transformation".

Positioning

Geopositioning, or simply positioning, is the determination of the location, as defined by a set of geodetic coordinates, of a point on land, at sea, or in space within a coordinate system (point positioning) or relative to another point (relative positioning). One computes the position of a point in space from measurements linking terrestrial or extraterrestrial points of known location ("known points") with terrestrial ones of unknown location ("unknown points"). The computation may involve transformations between or among astronomical and terrestrial coordinate systems. Known points used in point positioning can be GNSS satellites or triangulation points of a higher-order network.

Traditionally, geodesists built a hierarchy of networks to allow point positioning within a country. The highest in this hierarchy were triangulation networks, densified into the networks of traverses (polygons) into which local mapping and surveying measurements, usually collected using a measuring tape, a corner prism, and the red-and-white poles, are tied.

Commonly used nowadays is GPS, except for specialized measurements (e.g., in underground or high-precision engineering). The higher-order networks are measured with static GPS, using differential measurement to determine vectors between terrestrial points. These vectors then get adjusted in a traditional network fashion. A global polyhedron of permanently operating GPS stations under the auspices of the IERS is the basis for defining a single global, geocentric reference frame that serves as the "zero-order" (global) reference to which national measurements are attached.

Real-time kinematic positioning (RTK GPS) is employed frequently in survey mapping. In that measurement technique, unknown points can get quickly tied into nearby terrestrial known points.

One purpose of point positioning is the provision of known points for mapping measurements, also known as (horizontal and vertical) control. There can be thousands of those geodetically determined points in a country, usually documented by national mapping agencies. Surveyors involved in real estate and insurance will use these to tie their local measurements.

Geodetic problems

In geometrical geodesy, there are two main problems:

 * First (direct or forward) geodetic problem

 * Given the coordinates of a point and the directional (azimuth) and distance to a second point, determine the coordinates of that second point.

 * Second (inverse or reverse) geodetic problem

 * Given the coordinates of two points, determine the azimuth and length of the (straight, curved, or geodesic) line connecting those points.

The solutions to both problems in plane geometry reduce to simple trigonometry and are valid for small areas on Earth's surface; on a sphere, solutions become significantly more complex as, for example, in the inverse problem, the azimuths differ going between the two end points along the arc of the connecting great circle.

The general solution is called the geodesic for the surface considered, and the differential equations for the geodesic are solvable numerically. On the ellipsoid of revolution, geodesics are expressible in terms of elliptic integrals, which are usually evaluated in terms of a series expansion — see, for example, Vincenty's formulae.

Observational concepts

As defined in geodesy (and also astronomy), some basic observational concepts like angles and coordinates include (most commonly from the viewpoint of a local observer):

 * Plumbline or vertical: (the line along) the direction of local gravity.
 * Zenith: the (direction to the) intersection of the upwards-extending gravity vector at a point and the celestial sphere.
 * Nadir: the (direction to the) antipodal point where the downward-extending gravity vector intersects the (obscured) celestial sphere.
 * Celestial horizon: a plane perpendicular to the gravity vector at a point.
 * Azimuth: the direction angle within the plane of the horizon, typically counted clockwise from the north (in geodesy and astronomy) or the south (in France).
 * Elevation: the angular height of an object above the horizon; alternatively: zenith distance equal to 90 degrees minus elevation.
 * Local topocentric coordinates: azimuth (direction angle within the plane of the horizon), elevation angle (or zenith angle), distance.
 * North celestial pole: the extension of Earth's (precessing and nutating) instantaneous spin axis extended northward to intersect the celestial sphere. (Similarly for the south celestial pole.)
 * Celestial equator: the (instantaneous) intersection of Earth's equatorial plane with the celestial sphere.
 * Meridian plane: any plane perpendicular to the celestial equator and containing the celestial poles.
 * Local meridian: the plane which contains the direction to the zenith and the celestial pole.

Measurements

The reference surface (level) used to determine height differences and height reference systems is known as mean sea level. The traditional spirit level directly produces such (for practical purposes most useful) heights above sea level; 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 determination improves, one may expect that the use of GPS in height determination shall increase, too.

The theodolite is an instrument used to measure horizontal and vertical (relative to the local vertical) angles to target points. In addition, the tachymeter determines, electronically or electro-optically, the distance to a target and is highly automated or even robotic in operations. Widely used for the same purpose is the method of free station position.

Commonly for local detail surveys, tachymeters are employed, although the old-fashioned rectangular technique using an angle prism and steel tape is still an inexpensive alternative. As mentioned, also there are quick and relatively accurate real-time kinematic (RTK) GPS techniques. Data collected are tagged and recorded digitally for entry into Geographic Information System (GIS) databases.

Geodetic GNSS (most commonly GPS) receivers directly produce 3D coordinates in a geocentric coordinate frame. One such frame is WGS84, as well as frames by the International Earth Rotation and Reference Systems Service (IERS). GNSS receivers have almost completely replaced terrestrial instruments for large-scale base network surveys.

To monitor the Earth's rotation irregularities and plate tectonic motions and for planet-wide geodetic surveys, methods of very-long-baseline interferometry (VLBI) measuring distances to quasars, lunar laser ranging (LLR) measuring distances to prisms on the Moon, and satellite laser ranging (SLR) measuring distances to prisms on artificial satellites, are employed.

Gravity is measured using gravimeters, of which there are two kinds. First are absolute gravimeters, based on measuring the acceleration of free fall (e.g., of a reflecting prism in a vacuum tube). They are used to establish vertical geospatial control or in the field. Second, relative gravimeters are spring-based and more common. They are used in gravity surveys over large areas — to establish the figure of the geoid over these areas. The most accurate relative gravimeters are called superconducting gravimeters, which are sensitive to one-thousandth of one-billionth of Earth-surface gravity. Twenty-some superconducting gravimeters are used worldwide in studying Earth's tides, rotation, interior, oceanic and atmospheric loading, as well as in verifying the Newtonian constant of gravitation.

In the future, gravity and altitude might become measurable using the special-relativistic concept of time dilation as gauged by optical clocks.

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 direction 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 reasonably well when one also uses an ellipsoidal model of the figure of the Earth.

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 same as with the nautical mile.

A metre was originally defined as the 10-millionth part of the length from the equator to the North Pole along the meridian through Paris (the target was not quite reached in actual implementation, as it is off by 200 ppm in the current definitions). This situation means that one kilometre roughly equals (1/40,000) * 360 * 60 meridional minutes of arc, or 0.54 nautical miles. (This is not exactly so as the two units had been defined on different bases, so the international nautical mile is 1,852 m exactly, which corresponds to the rounding of 1,000/0.54 m to four digits).

Temporal changes

Various techniques are used in geodesy to study temporally changing surfaces, bodies of mass, physical fields, and dynamical systems. Points on Earth's surface change their location due to a variety of mechanisms:

 * Continental plate motion, plate tectonics
 * The episodic motion of tectonic origin, especially close to fault lines
 * Periodic effects due to tides and tidal loading
 * Postglacial land uplift due to isostatic adjustment
 * Mass variations due to hydrological changes, including the atmosphere, cryosphere, land hydrology, and oceans
 * Sub-daily polar motion
 * Length-of-day variability
 * Earth's center-of-mass (geocenter) variations
 * Anthropogenic movements such as reservoir construction or petroleum or water extraction

Geodynamics is the discipline that studies deformations and motions of Earth's crust and its solidity as a whole. Often the study of Earth's irregular rotation is included in the above definition. Geodynamical studies require terrestrial reference frames realized by the stations belonging to the Global Geodetic Observing System (GGOS ).

Techniques for studying geodynamic phenomena on global scales include:

 * Satellite positioning by GPS, GLONASS, Galileo, and BeiDou
 * Very-long-baseline interferometry (VLBI)
 * Satellite laser ranging (SLR) and lunar laser ranging (LLR)
 * DORIS
 * Regionally and locally precise leveling
 * Precise tachymeters
 * Monitoring of gravity change using land, airborne, shipborne, and spaceborne gravimetry
 * Satellite altimetry based on microwave and laser observations for studying the ocean surface, sea level rise, and ice cover monitoring
 * Interferometric synthetic aperture radar (InSAR) using satellite images.

title: Geodesy


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Eurogame

A Eurogame, also called a German-style board game, German game, or Euro-style game (generally just referred to as board games in Europe), is a class of tabletop games that generally has indirect player interaction and multiple ways to score points. Eurogames are sometimes contrasted with American-style board games, which generally involve more luck, conflict, and drama. They are usually less abstract than chess or Go, but more abstract than wargames. Likewise, they generally require more thought and planning than party games such as Pictionary or Trivial Pursuit.

History
Due in part to postwar aversion to products which glorified conflict, the 3M series of strategy and economic games, including Acquire, became popular in Germany and provided a template for a new form of gameplay without direct conflict or warfare.

German family board games
The genre developed as a more concentrated design movement in the late 1970s and early 1980s in Germany. The genre has spread to other European countries such as France, the Netherlands, and Sweden. The Settlers of Catan, first published in 1995, paved the way for the genre outside Europe. Though neither the first Eurogame nor the first such game to find an audience outside Germany, it became much more popular than any of its predecessors. It quickly sold millions of copies in Germany, and in the process brought money and attention to the genre as a whole.

21st century
Residents of Germany purchased more board games per capita than any other country. While many Eurogames are published and played in Anglophone markets such as the United States and the United Kingdom, they occupy a niche status there. Other games in the genre to achieve widespread popularity include Carcassonne, Puerto Rico, Ticket to Ride, and Alhambra.

Characteristics

Eurogames tend to be focused on challenge for players. They feature economics and the acquisition of resources rather than direct conflict, and have a limited amount of luck. They also differ from abstract strategy games like chess by using themes tied to specific locales, and emphasize individual development and comparative achievement rather than direct conflict. Eurogames also emphasize the mechanical challenges of their systems over having the systems match the theme of the game. They are generally simpler than the wargames that flourished in the 1970s and 1980s from publishers such as SPI and Avalon Hill, but nonetheless often have a considerable depth of play.

One consequence of the increasing popularity of this genre has been an expansion upwards in complexity. Games such as Puerto Rico that were considered quite complex when Eurogames proliferated in the U.S. after the turn of the millennium are now the norm, with newer high-end titles like Terra Mystica and Tzolkin being significantly more difficult to master.

Incentive for social play
While many titles (especially the strategically heavier ones) are enthusiastically played by gamers as a hobby, Eurogames are, for the most part, well-suited to social play. In keeping with this social function, various characteristics of the games tend to support that aspect well, and these have become quite common across the genre. In contrast to games such as Risk or Monopoly, in which a close game can extend indefinitely, Eurogames usually have a mechanism to stop the game within its stated playing time. Common mechanisms include a pre-determined winning score, a set number of game turns, or depletion of limited game resources. Playing time varies from a half-hour to a few hours, with one to two hours being typical. Generally Eurogames do not have a fixed number of players like chess or bridge; although there is a sizeable body of German-style games that are designed for exactly two players, most games can accommodate anywhere from two to six players (with varying degrees of suitability). Six-player games are somewhat rare, with Power Grid and Caverna (the latter supporting seven player games) being two examples, or require expansions, as with The Settlers of Catan or Carcassonne. Players usually play for themselves individually, rather than in a partnership or team.

A growing number of Eurogames support solo play with modified rulesets. To win, the player either has to achieve specific single-player campaign goals or beat the score of a simulated opponent that takes actions according to special rules outlined in the scenario. Recent Eurogames suitable for solo play include Wingspan, Terraforming Mars, and Spirit Island.

No player elimination
Another prominent characteristic of these games is the lack of player elimination. Eliminating players before the end of the game is seen as contrary to the social aspect of such games. Most of these games are designed to keep all players in the game as long as possible, so it is rare to be certain of victory or defeat until relatively late in the game. Related to no-player-elimination, Eurogame scoring systems are often designed so that hidden scoring or end-of-game bonuses can catapult a player who appears to be in a lagging position at end of play into the lead. A second-order consequence is that Eurogames tend to have multiple paths to victory (dependent on aiming at different end-of-game bonuses) and it is often not obvious to other players which strategic path a player is pursuing. Balancing mechanisms are often integrated into the rules, giving slight advantages to lagging players and slight hindrances to the leaders. This helps to keep the game competitive to the very end, an example of which is Power Grid, where the turn order is determined by number of cities (and biggest power plant as the tie-breaker), such that players further ahead are handicapped in their option of plays.

Game mechanics
A wide variety of often innovative mechanisms or mechanics are used, and familiar mechanics such as rolling dice and moving, capture, or trick taking are avoided. If a game has a board, the board is usually irregular rather than uniform or symmetric (such as Risk rather than chess or Scrabble). The board is often random (as in The Settlers of Catan) or has random elements (such as Tikal). Some boards are merely mnemonic or organizational and contribute only to ease of play, such as a cribbage board; examples of this include Puerto Rico and Princes of Florence. Random elements are often present but do not usually dominate the game. While rules are light to moderate, they allow depth of play, usually requiring thought, planning, and a shift of tactics through the game and featuring a chess- or backgammon-like opening game, middle game, and end game.

Stewart Woods' Eurogames cites six examples of mechanics common to eurogames:

 * Tile Placement – spatial placement of game components on the playing board.
 * Auctions – includes open and hidden auctions of both resources and actions from other players and the game system itself.
 * Trading/Negotiation – not simply trading resources of equivalent values, but allowing players to set markets.
 * Set Collection – collecting resources in specific groups that are then cashed in for points or other currency.
 * Area Control – also known as area majority or influence, this involves controlling a game element or board space through allocation of resources.
 * Worker Placement or Role Selection – players choose specific game actions in sequential order, with players disallowed from choosing a previously selected action.

Low randomness
Eurogame designs tend to de-emphasize luck and random elements. Often, the only random element of the game will be resource or terrain distribution in the initial setup, or (less frequently) the random order of a set of event or objective cards. The role played by deliberately random mechanics in other styles of game is instead fulfilled by the unpredictability of the behavior of other players.

Themes
Examples of themes are:
 * Carcassonne – build a medieval landscape complete with walled cities, monasteries, roads, and fields.
 * Puerto Rico – develop plantations on the island of Puerto Rico, set in the 18th century.
 * Power Grid – expand a power company's network and buy better plants.
 * Imperial – as an international investor, influence the politics of pre-World War I European empires.
 * Bruxelles 1893 – take the role of an Art Nouveau architect during the late 19th century and try to become the most famous architect in Belgium.

Game designer as author
Although not relevant to actual play, the name of the game's designer is often prominently mentioned on the box, or at least in the rule book. Top designers enjoy considerable following among enthusiasts of Eurogames. For this reason, the name "designer games" is often offered as a description of the genre. Recently, there has also been a wave of games designed as spin-offs of popular novels, such as the games taking their style from the German bestsellers Der Schwarm and Tintenherz.

Designers
Designers of Eurogames include:
 * Antoine Bauza, a prolific French designer, creator of 7 Wonders, Tokaido, and Takenoko.
 * Bruno Cathala, a French-born game designer, creator of Kingdomino and Five Tribes.
 * Vlaada Chvátil, a Czech designer of board games and video games, whose games include Through the Ages: A Story of Civilization, Galaxy Trucker, Space Alert, and Codenames. His rule books are often divided into several "learning scenarios" that gradually introduce players to the rules as they progress through the scenarios.
 * Leo Colovini, designer of Cartagena and Carcassonne: The Discovery.
 * Rüdiger Dorn, a German designer who created Istanbul, Karuba, Las Vegas, Luxor, and others.
 * Bruno Faidutti, French designer of Citadels.
 * Stefan Feld, designer particularly of games that make use of dice, and that allow players to score points in a variety of ways. He has designed games such as Castles of Burgundy and Trajan, and three of his games (Strasbourg, Bruges, and Carpe Diem) have been nominated for the Kennerspiel des Jahres.
 * Friedemann Friese, a German designer, creator of Power Grid, as well as many others.
 * Mac Gerdts, a German designer of games such as Antike, Imperial, Navegador, and Concordia.
 * Reiner Knizia, one of the most prolific German game designers, having designed over 600 published games. Recurring mechanisms in his games include auctions (Ra and Modern Art), tile placement (Tigris and Euphrates and Ingenious), and intricate scoring rules (Samurai). He has also designed many card games such as Lost Cities, Schotten-Totten, and Blue Moon, and the cooperative board game The Lord of the Rings.
 * Wolfgang Kramer, who often works with other game designers. His titles include El Grande, Tikal, Princes of Florence, and Torres. His games often have some sort of action point system, and include some geometric element.
 * Alan R. Moon, a British-born designer with numerous games to his credit, often with a railway theme, including the Spiel des Jahres-winning Ticket to Ride and Elfenland.
 * Alex Randolph, who created over 125 games and is responsible for the placement of the author's name on the rules and box.
 * Uwe Rosenberg, designer of games such as Agricola, Le Havre, Patchwork, and several others.
 * Sid Sackson was a prolific American game designer whose games, particularly Acquire, prefigured and strongly influenced the Eurogame genre.
 * Michael Schacht, German designer of Coloretto, Zooloretto, Aquaretto, Valdora, Africana, Web of power, China, Han, Hansa, Mondo, Mondo Sapiens, Spirits of the Forest, Coney Island.
 * Andreas Seyfarth, who has designed the games Puerto Rico, Manhattan, and, with Karen Seyfarth, Thurn and Taxis.
 * Klaus Teuber, designer of Catan, which has sold more than 22 million copies.
 * Klaus-Jürgen Wrede, the German game designer of the Carcassonne board game series., Carcassonne has 11 expansions and 6 variant standalone games available as well as numerous mini-expansions.

Events
The Internationale Spieltage, also known as Essen Spiel, or the Essen Games Fair, is the largest non-digital game convention in the world, and the place where the largest number of Eurogames are released each year. Founded in 1983 and held annually in Essen, Germany, the fair was founded with the objective of providing a venue for people to meet and play board games, and show gaming as an integral part of German culture.

A "World Boardgaming Championships" is held annually in July in Pennsylvania, USA. The event is nine days long and includes tournament tracks of over a hundred games; while traditional wargames are played there, all of the most popular tournaments are Eurogames and it is generally perceived as a Eurogame-centered event. Attendance is international, though players from the U.S. and Canada predominate.

Awards
The most prestigious German board game award is the Spiel des Jahres ("Game of the Year"). The award is very family-oriented, with shorter, more approachable games such as Ticket to Ride and Elfenland usually preferred by the committee that gives out the award.

In 2011, the jury responsible for the Spiel des Jahres created the Kennerspiel des Jahres, or connoisseur's game of the year, for more complex games.

The Deutscher Spiele Preis ("German game prize") is also awarded to games that are more complex and strategic, such as Puerto Rico. However, there are a few games with broad enough appeal to win both awards: The Settlers of Catan (1995), Carcassonne (2001), Dominion (2009).

Influence
Xbox Live Arcade has included popular games from the genre, with Catan being released to strong sales on May 13, 2007, Carcassonne being released on June 27, 2007. Lost Cities and Ticket to Ride soon followed. Alhambra was due to follow later in 2007 until being cancelled.

The iPhone received versions of The Settlers of Catan and Zooloretto in 2009. Carcassonne was added to the iPhone App Store in June 2010. Later, Ticket to Ride was developed for both the iPhone and the iPad, significantly boosting sales of the board game.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Eurogame


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Grand Unified Theory

Grand Unified Theory (GUT) is any model in particle physics that merges the electromagnetic, weak, and strong forces (the three gauge interactions of the Standard Model) into a single force at high energies. Although this unified force has not been directly observed, many GUT models theorize its existence. If the unification of these three interactions is possible, it raises the possibility that there was a grand unification epoch in the very early universe in which these three fundamental interactions were not yet distinct.

Experiments have confirmed that at high energy, the electromagnetic interaction and weak interaction unify into a single combined electroweak interaction. GUT models predict that at even higher energy, the strong and electroweak interactions will unify into one electronuclear interaction. This interaction is characterized by one larger gauge symmetry and thus several force carriers, but one unified coupling constant. Unifying gravity with the electronuclear interaction would provide a more comprehensive theory of everything (TOE) rather than a Grand Unified Theory. Thus, GUTs are often seen as an intermediate step towards a TOE.

The novel particles predicted by GUT models are expected to have extremely high masses—around the GUT scale of $$ 10^{16} $$ GeV (just three orders of magnitude below the Planck scale of $$ 10^{19} $$ GeV)—and so are well beyond the reach of any foreseen particle hadron collider experiments. Therefore, the particles predicted by GUT models will be unable to be observed directly, and instead the effects of grand unification might be detected through indirect observations of the following:

 * proton decay,
 * electric dipole moments of elementary particles,
 * or the properties of neutrinos.

Some GUTs, such as the Pati–Salam model, predict the existence of magnetic monopoles.

While GUTs might be expected to offer simplicity over the complications present in the Standard Model, realistic models remain complicated because they need to introduce additional fields and interactions, or even additional dimensions of space, in order to reproduce observed fermion masses and mixing angles. This difficulty, in turn, may be related to the existence of family symmetries beyond the conventional GUT models. Due to this and the lack of any observed effect of grand unification so far, there is no generally accepted GUT model.

Models that do not unify the three interactions using one simple group as the gauge symmetry but do so using semisimple groups can exhibit similar properties and are sometimes referred to as Grand Unified Theories as well.

History
Historically, the first true GUT, which was based on the simple Lie group $SU(5)$, was proposed by Howard Georgi and Sheldon Glashow in 1974. The Georgi–Glashow model was preceded by the semisimple Lie algebra Pati–Salam model by Abdus Salam and Jogesh Pati also in 1974, who pioneered the idea to unify gauge interactions.

The acronym GUT was first coined in 1978 by CERN researchers John Ellis, Andrzej Buras, Mary K. Gaillard, and Dimitri Nanopoulos, however in the final version of their paper they opted for the less anatomical GUM (Grand Unification Mass). Nanopoulos later that year was the first to use the acronym in a paper.

Motivation
The fact that the electric charges of electrons and protons seem to cancel each other exactly to extreme precision is essential for the existence of the macroscopic world as we know it, but this important property of elementary particles is not explained in the Standard Model of particle physics. While the description of strong and weak interactions within the Standard Model is based on gauge symmetries governed by the simple symmetry groups $SU(3)$ and $SU(2)$ which allow only discrete charges, the remaining component, the weak hypercharge interaction is described by an abelian symmetry $U(1)$ which in principle allows for arbitrary charge assignments. The observed charge quantization, namely the postulation that all known elementary particles carry electric charges which are exact multiples of one-third of the "elementary" charge, has led to the idea that hypercharge interactions and possibly the strong and weak interactions might be embedded in one Grand Unified interaction described by a single, larger simple symmetry group containing the Standard Model. This would automatically predict the quantized nature and values of all elementary particle charges. Since this also results in a prediction for the relative strengths of the fundamental interactions which we observe, in particular, the weak mixing angle, grand unification ideally reduces the number of independent input parameters but is also constrained by observations.

Grand unification is reminiscent of the unification of electric and magnetic forces by Maxwell's field theory of electromagnetism in the 19th century, but its physical implications and mathematical structure are qualitatively different.

SU(5)

$SU(5)$ is the simplest GUT. The smallest simple Lie group which contains the standard model, and upon which the first Grand Unified Theory was based, is

 * $$ \rm SU(5) \supset SU(3)\times SU(2)\times U(1)$$.

Such group symmetries allow the reinterpretation of several known particles, including the photon, W and Z bosons, and gluon, as different states of a single particle field. However, it is not obvious that the simplest possible choices for the extended "Grand Unified" symmetry should yield the correct inventory of elementary particles. The fact that all currently known matter particles fit perfectly into three copies of the smallest group representations of $5 + 10$ and immediately carry the correct observed charges, is one of the first and most important reasons why people believe that a Grand Unified Theory might actually be realized in nature.

The two smallest irreducible representations of $SU(5)$ are $SU(5)$ (the defining representation) and $SU(5)$. (These bold numbers indicate the dimension of the representation.) In the standard assignment, the $5$ contains the charge conjugates of the right-handed down-type quark color triplet and a left-handed lepton isospin doublet, while the $10$ contains the six up-type quark components, the left-handed down-type quark color triplet, and the right-handed electron. This scheme has to be replicated for each of the three known generations of matter. It is notable that the theory is anomaly free with this matter content.

The hypothetical right-handed neutrinos are a singlet of $5$, which means its mass is not forbidden by any symmetry; it doesn't need a spontaneous electroweak symmetry breaking which explains why its mass would be heavy (see seesaw mechanism).

SO(10)

The next simple Lie group which contains the standard model is

 * $$\rm SO(10)\supset SU(5)\supset SU(3)\times SU(2)\times U(1)$$.

Here, the unification of matter is even more complete, since the irreducible spinor representation $10$ contains both the $SU(5)$ and $16$ of $\overline{5}$ and a right-handed neutrino, and thus the complete particle content of one generation of the extended standard model with neutrino masses. This is already the largest simple group that achieves the unification of matter in a scheme involving only the already known matter particles (apart from the Higgs sector).

Since different standard model fermions are grouped together in larger representations, GUTs specifically predict relations among the fermion masses, such as between the electron and the down quark, the muon and the strange quark, and the tau lepton and the bottom quark for $10$ and $SU(5)$. Some of these mass relations hold approximately, but most don't (see Georgi-Jarlskog mass relation).

The boson matrix for $SU(5)$ is found by taking the $SO(10)$ matrix from the $SO(10)$ representation of $15 × 15$ and adding an extra row and column for the right-handed neutrino. The bosons are found by adding a partner to each of the 20 charged bosons (2 right-handed W bosons, 6 massive charged gluons and 12 X/Y type bosons) and adding an extra heavy neutral Z-boson to make 5 neutral bosons in total. The boson matrix will have a boson or its new partner in each row and column. These pairs combine to create the familiar 16D Dirac spinor matrices of $10 + 5$.

E6
In some forms of string theory, including E8 × E8 heterotic string theory, the resultant four-dimensional theory after spontaneous compactification on a six-dimensional Calabi–Yau manifold resembles a GUT based on the group E6. Notably E6 is the only exceptional simple Lie group to have any complex representations, a requirement for a theory to contain chiral fermions (namely all weakly-interacting fermions). Hence the other four (G2, F4, E7, and E8) can't be the gauge group of a GUT.

Extended Grand Unified Theories
Non-chiral extensions of the Standard Model with vectorlike split-multiplet particle spectra which naturally appear in the higher SU(N) GUTs considerably modify the desert physics and lead to the realistic (string-scale) grand unification for conventional three quark-lepton families even without using supersymmetry (see below). On the other hand, due to a new missing VEV mechanism emerging in the supersymmetric SU(8) GUT the simultaneous solution to the gauge hierarchy (doublet-triplet splitting) problem and problem of unification of flavor can be argued.

GUTs with four families / generations, SU(8): Assuming 4 generations of fermions instead of 3 makes a total of $SU(5)$ types of particles. These can be put into $SO(10)$ representations of $64$. This can be divided into $64 = 8 + 56$ which is the $SU(8)$ theory together with some heavy bosons which act on the generation number.

GUTs with four families / generations, O(16): Again assuming 4 generations of fermions, the 128 particles and anti-particles can be put into a single spinor representation of $SU(5) × SU(3)_{F} × U(1)$.

Symplectic groups and quaternion representations
Symplectic gauge groups could also be considered. For example, $SU(5)$ (which is called $O(16)$ in the article symplectic group) has a representation in terms of $Sp(8)$ quaternion unitary matrices which has a $Sp(4)$ dimensional real representation and so might be considered as a candidate for a gauge group. $4 × 4$ has 32 charged bosons and 4 neutral bosons. Its subgroups include $16$ so can at least contain the gluons and photon of $Sp(8)$. Although it's probably not possible to have weak bosons acting on chiral fermions in this representation. A quaternion representation of the fermions might be:

\begin{bmatrix} e  + i\ \overline{e}            + j\ v             + k\ \overline{v} \\ u_r + i\ \overline{u}_\mathrm{\overline r} + j\ d_\mathrm{r} + k\ \overline{d}_\mathrm{\overline r} \\ u_g + i\ \overline{u}_\mathrm{\overline g} + j\ d_\mathrm{g} + k\ \overline{d}_\mathrm{\overline g} \\ u_b + i\ \overline{u}_\mathrm{\overline b} + j\ d_\mathrm{b} + k\ \overline{d}_\mathrm{\overline b} \\ \end{bmatrix}_\mathrm{L} $$

A further complication with quaternion representations of fermions is that there are two types of multiplication: left multiplication and right multiplication which must be taken into account. It turns out that including left and right-handed $SU(4)$ quaternion matrices is equivalent to including a single right-multiplication by a unit quaternion which adds an extra SU(2) and so has an extra neutral boson and two more charged bosons. Thus the group of left- and right-handed $SU(3) × U(1)$ quaternion matrices is $4 × 4$ which does include the standard model bosons:

 * $$ \mathrm{ SU(4,\mathbb{H})_L\times \mathbb{H}_R = Sp(8)\times SU(2) \supset SU(4)\times SU(2) \supset SU(3)\times SU(2)\times U(1) }$$

If $$\psi$$ is a quaternion valued spinor, $$\ A^{ab}_\mu\ $$ is quaternion hermitian $4 × 4$ matrix coming from $Sp(8) × SU(2)$ and $$\ B_\mu\ $$ is a pure vector quaternion (both of which are 4-vector bosons) then the interaction term is:

 * $$\ \overline{\psi^{a}} \gamma_\mu\left( A^{ab}_\mu\psi^b + \psi^a B_\mu \right)\ $$

Octonion representations
It can be noted that a generation of 16 fermions can be put into the form of an octonion with each element of the octonion being an 8-vector. If the 3 generations are then put in a 3x3 hermitian matrix with certain additions for the diagonal elements then these matrices form an exceptional (Grassmann) Jordan algebra, which has the symmetry group of one of the exceptional Lie groups ($4 × 4$$4$, $Sp(8)$$6$, $F$$7$, or $E$$8$) depending on the details.

\psi= \begin{bmatrix} a & e & \mu \\ \overline{e} & b & \tau \\ \overline{\mu} & \overline{\tau} & c \end{bmatrix} $$

 * $$\ [\psi_A,\psi_B] \subset \mathrm{J}_3(\mathbb{O})\ $$

Because they are fermions the anti-commutators of the Jordan algebra become commutators. It is known that $E$$6$ has subgroup $E$ and so is big enough to include the Standard Model. An $E$$8$ gauge group, for example, would have 8 neutral bosons, 120 charged bosons and 120 charged anti-bosons. To account for the 248 fermions in the lowest multiplet of $O(10)$$8$, these would either have to include anti-particles (and so have baryogenesis), have new undiscovered particles, or have gravity-like (spin connection) bosons affecting elements of the particles spin direction. Each of these possesses theoretical problems.

Beyond Lie groups
Other structures have been suggested including Lie 3-algebras and Lie superalgebras. Neither of these fit with Yang–Mills theory. In particular Lie superalgebras would introduce bosons with incorrect statistics. Supersymmetry, however, does fit with Yang–Mills.

Unification of forces and the role of supersymmetry
The unification of forces is possible due to the energy scale dependence of force coupling parameters in quantum field theory called renormalization group "running", which allows parameters with vastly different values at usual energies to converge to a single value at a much higher energy scale.

The renormalization group running of the three gauge couplings in the Standard Model has been found to nearly, but not quite, meet at the same point if the hypercharge is normalized so that it is consistent with $E$ or $E$ GUTs, which are precisely the GUT groups which lead to a simple fermion unification. This is a significant result, as other Lie groups lead to different normalizations. However, if the supersymmetric extension MSSM is used instead of the Standard Model, the match becomes much more accurate. In this case, the coupling constants of the strong and electroweak interactions meet at the grand unification energy, also known as the GUT scale:

 * $$\Lambda_{\text{GUT}} \approx 10^{16}\,\text{GeV}$$.

It is commonly believed that this matching is unlikely to be a coincidence, and is often quoted as one of the main motivations to further investigate supersymmetric theories despite the fact that no supersymmetric partner particles have been experimentally observed. Also, most model builders simply assume supersymmetry because it solves the hierarchy problem—i.e., it stabilizes the electroweak Higgs mass against radiative corrections.

Neutrino masses
Since Majorana masses of the right-handed neutrino are forbidden by $SU(5)$ symmetry, $SO(10)$ GUTs predict the Majorana masses of right-handed neutrinos to be close to the GUT scale where the symmetry is spontaneously broken in those models. In supersymmetric GUTs, this scale tends to be larger than would be desirable to obtain realistic masses of the light, mostly left-handed neutrinos (see neutrino oscillation) via the seesaw mechanism. These predictions are independent of the Georgi–Jarlskog mass relations, wherein some GUTs predict other fermion mass ratios.

Proposed theories
Several theories have been proposed, but none is currently universally accepted. An even more ambitious theory that includes all fundamental forces, including gravitation, is termed a theory of everything. Some common mainstream GUT models are:

 * Pati–Salam model — $SO(10)$
 * Georgi–Glashow model — $SO(10)$; and Flipped $SU(4) × SU(2) × SU(2)$ — $SU(5)$
 * $SU(5)$ model; and Flipped $SU(5) × U(1)$ — $SO(10)$
 * $SO(10)$ model; and Trinification — $SO(10) × U(1)$
 * minimal left-right model — $E6$
 * 331 model — $SU(3) × SU(3) × SU(3)$
 * chiral color

Not quite GUTs:

 * Technicolor models
 * Little Higgs
 * String theory
 * Causal fermion systems
 * M-theory
 * Preons
 * Loop quantum gravity
 * Causal dynamical triangulation theory

Note: These models refer to Lie algebras not to Lie groups. The Lie group could be $$[\text{SU}(4) \times \text{SU}(2) \times \text{SU}(2)] / \mathbb{Z}_2,$$ just to take a random example.

The most promising candidate is $SU(3)C × SU(2)L × SU(2)R × U(1)B − L$. (Minimal) $SU(3)C × SU(3)L × U(1)X$ does not contain any exotic fermions (i.e. additional fermions besides the Standard Model fermions and the right-handed neutrino), and it unifies each generation into a single irreducible representation. A number of other GUT models are based upon subgroups of $SO(10)$. They are the minimal left-right model, $SO(10)$, flipped $SO(10)$ and the Pati–Salam model. The GUT group $SU(5)$ contains $SU(5)$, but models based upon it are significantly more complicated. The primary reason for studying $E6$ models comes from $SO(10)$ heterotic string theory.

GUT models generically predict the existence of topological defects such as monopoles, cosmic strings, domain walls, and others. But none have been observed. Their absence is known as the monopole problem in cosmology. Many GUT models also predict proton decay, although not the Pati–Salam model. As of now, proton decay has never been experimentally observed. The minimal experimental limit on the proton's lifetime pretty much rules out minimal $E6$ and heavily constrains the other models. The lack of detected supersymmetry to date also constrains many models.

Some GUT theories like $E8 × E8$ and $SU(5)$ suffer from what is called the doublet-triplet problem. These theories predict that for each electroweak Higgs doublet, there is a corresponding colored Higgs triplet field with a very small mass (many orders of magnitude smaller than the GUT scale here). In theory, unifying quarks with leptons, the Higgs doublet would also be unified with a Higgs triplet. Such triplets have not been observed. They would also cause extremely rapid proton decay (far below current experimental limits) and prevent the gauge coupling strengths from running together in the renormalization group.

Most GUT models require a threefold replication of the matter fields. As such, they do not explain why there are three generations of fermions. Most GUT models also fail to explain the little hierarchy between the fermion masses for different generations.

Ingredients
A GUT model consists of a gauge group which is a compact Lie group, a connection form for that Lie group, a Yang–Mills action for that connection given by an invariant symmetric bilinear form over its Lie algebra (which is specified by a coupling constant for each factor), a Higgs sector consisting of a number of scalar fields taking on values within real/complex representations of the Lie group and chiral Weyl fermions taking on values within a complex rep of the Lie group. The Lie group contains the Standard Model group and the Higgs fields acquire VEVs leading to a spontaneous symmetry breaking to the Standard Model. The Weyl fermions represent matter.

Current evidence
The discovery of neutrino oscillations indicates that the Standard Model is incomplete, but there is currently no clear evidence that nature is described by any Grand Unified Theory. Neutrino oscillations have led to renewed interest toward certain GUT such as $X$.

One of the few possible experimental tests of certain GUT is proton decay and also fermion masses. There are a few more special tests for supersymmetric GUT. However, minimum proton lifetimes from research (at or exceeding the ~ year range) have ruled out simpler GUTs and most non-SUSY models. The maximum upper limit on proton lifetime (if unstable), is calculated at 6× years for SUSY models and 1.4× years for minimal non-SUSY GUTs.

The gauge coupling strengths of QCD, the weak interaction and hypercharge seem to meet at a common length scale called the GUT scale and equal approximately to GeV (slightly less than the Planck energy of  GeV), which is somewhat suggestive. This interesting numerical observation is called the gauge coupling unification, and it works particularly well if one assumes the existence of superpartners of the Standard Model particles. Still, it is possible to achieve the same by postulating, for instance, that ordinary (non supersymmetric) $X$ models break with an intermediate gauge scale, such as the one of Pati–Salam group.

Ultra unification
In 2020, physicist Juven Wang introduced a concept known as "ultra unification". It combines the Standard Model and grand unification, particularly for the models with 15 Weyl fermions per generation, without the necessity of right-handed sterile neutrinos, by adding new gapped topological phase sectors or new gapless interacting conformal sectors consistent with the nonperturbative global anomaly cancellation and cobordism constraints (especially from the mixed gauge-gravitational anomaly, such as a Z/16Z class anomaly, associated with the baryon minus lepton number B−L and the electroweak hypercharge Y).

Gapped topological phase sectors are constructed via the symmetry extension (in contrast to the symmetry breaking in the Standard Model's Anderson-Higgs mechanism), whose low energy contains unitary Lorentz invariant topological quantum field theories (TQFTs), such as 4-dimensional noninvertible, 5-dimensional noninvertible, or 5-dimensional invertible entangled gapped phase TQFTs.

Alternatively, Wang's theory suggests there could also be right-handed sterile neutrinos, gapless unparticle physics, or some combination of more general interacting conformal field theories (CFTs), to together cancel the mixed gauge-gravitational anomaly. This proposal can also be understood as coupling the Standard Model (as quantum field theory) to the Beyond the Standard Model sector (as TQFTs or CFTs being dark matter) via the discrete gauged B−L topological force.

In either TQFT or CFT scenarios, the implication is that a new high-energy physics frontier beyond the conventional 0-dimensional particle physics relies on new types of topological forces and matter. This includes gapped extended objects such as 1-dimensional line and 2-dimensional surface operators or conformal defects, whose open ends carry deconfined fractionalized particle or anyonic string excitations.

Understanding and characterizing these gapped extended objects requires mathematical concepts such as cohomology, cobordism, or category into particle physics. The topological phase sectors proposed by Wang signify a departure from the conventional particle physics paradigm, indicating a frontier in beyond-the-Standard-Model physics.

title: Grand Unified Theory


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GTE

GTE Corporation, formerly General Telephone & Electronics Corporation (1955–1982), was the largest independent telephone company in the United States during the days of the Bell System. The company operated from 1926, with roots tracing further back than that, until 2000, when it was acquired by Bell Atlantic; the combined company took the name Verizon.

The Wisconsin-based Associated Telephone Utilities Company was founded in 1926; it went bankrupt in 1933 during the Great Depression, and was reorganized as General Telephone in 1934. In 1991, it acquired the third largest independent, Continental Telephone (ConTel). It owned Automatic Electric, a telephone equipment supplier similar in many ways to Western Electric, and Sylvania Lighting, the only non-communications-oriented company under GTE ownership. GTE provided local telephone service to many areas of the U.S. through operating companies, much as American Telephone & Telegraph provided local telephone service through its 22 Bell Operating Companies.

The company acquired BBN Planet, one of the earliest Internet service providers, in 1997. That division became known as GTE Internetworking, and was later spun off into the independent company Genuity (a name recycled from another Internet company GTE acquired in 1997) to satisfy Federal Communications Commission (FCC) requirements regarding the GTE–Bell Atlantic merger that created Verizon.

GTE operated in Canada via large interests in subsidiary companies such as BC Tel and Quebec-Téléphone. When foreign ownership restrictions on telecommunications companies were introduced, GTE's ownership was grandfathered. When BC Tel merged with Telus (the name given to the privatized Alberta Government Telephones (AGT)) to create BCT.Telus, GTE's Canadian subsidiaries were merged into the new parent, making it the second-largest telecommunications carrier in Canada. As such, GTE's successor, Verizon Communications, was the only foreign telecommunications company with a greater than 20% interest in a Canadian carrier, until Verizon completely divested itself of its shares in 2004.

In the Caribbean, CONTEL purchased several major stakes in the newly independent countries of the British West Indies (namely in Barbados, Jamaica, and Trinidad and Tobago).

Prior to GTE's merger with Bell Atlantic, GTE also maintained an interactive television service joint-venture called GTE mainStreet (sometimes also called mainStreet USA) as well as an interactive entertainment and video game publishing operation, GTE Interactive Media.

General Telephone
In 1934, General Telephone Corporation was established with John Winn as president. The following year, the company created General Telephone Directory Company as a division. During World War II, General Telephone helped install phone service for military facilities. From 1946 to 1950, General Telephone obtained over 100,000 telephone lines and bought out Leich Electric Company.

General Telephone's holdings included 15 telephone companies across 20 states by 1951, when Donald C. Power was named president of the company under chairman and long-time GT executive Morris F. LaCroix, replacing the retiring Harold Bozell (president 1940 – 1951). Power proceeded to expand the company through the 1950s principally through two acquisitions.

In 1955, Theodore Gary & Company became a part of General Telephone and allowed the company to hold over 2 million telephone lines after the company merge. It also had a subsidiary, named the General Telephone and Electric Corporation, formed in 1930 with the Transamerica Corporation and British investors to compete against ITT.

In 1959, Sylvania Electric Products merged into General Telephone and was renamed to General Telephone & Electronics Corporation (GT&E). Power also obtained the purchases of multiple companies. such as Lenkurt Electric Company, Inc and Peninsular Telephone Company. In 1960, GT&E International Incorporated was created as a branch company. Power was named C.E.O. and chairman in 1961, making way for Leslie H. Warner, formerly of Theodore Gary, to become president. Simultaneously, GT&E went on to buy Community Antenna Television providers.

In 1964, Western Utilities Corporation became part of GT&E. Additional purchases during the 1960s included Hawaiian Telephone Company and Northern Ohio Telephone Company. At the end of the decade, ten million GT&E phones were active.

In the late 1960s, GT&E joined in the search for a railroad car Automatic Car Identification system. It designed the KarTrak optical system, which won over other manufacturer's systems in field trials, but ultimately proved to need too much maintenance. In the late 1970s the system was abandoned.

After a 1970 bomb attack to the company's headquarters in New York City, the company relocated to Stamford, Connecticut for their new headquarters. In 1971 GT&E undertook an identity change and became simply GTE, while Sylvania Electric Products became GTE Sylvania. The same year, Donald C. Power retired and Leslie H. Warner became chairman of the board. Theodore F. Brophy was brought in as president.

In 1974, GTE worked with American Telephone & Telegraph in a project to create satellite stations. A few years later, the company's international branch was replaced by a GTE products company in 1976. Their products company remained until 1979. In 1979, GTE purchased Telenet to establish a presence in the growing packet switching data communications business. GTE Telenet was later included in the US Telecom joint venture.

1980s
In December 1983 Vanderslice stepped down as the company's president and chief operating officer.

In April 1988, after the retirement of Theodore F. Brophy, James L. "Rocky" Johnson was promoted from his position as president and chief operating officer to CEO of GTE; he was appointed chairman in 1991.

Under Johnson’s leadership, GTE divested its 50% ownership of U.S. Sprint, the nation’s third largest long distance company. He also orchestrated the sale of Sylvania and the merger with Contel, creating the 2nd largest telephone company in the United States. In 1989, GTE reorganized into six operating groups, focusing on its core businesses of telephone operations, information services, and publishing of telephone directories. With previous job cuts and announced future job cuts, Johnson was able to return GTE to profitability. Other new services provided under his leadership were GTE Mobilenet cellular telephone operations, Airfone air-to-ground telephone services, and the first voice, video, and data services community in Cerritos, California to test home banking, at-home shopping, home security, and pay-per-view television in 16,000 homes and 2,000 businesses.

1990s
In April 1992, James L. "Rocky" Johnson retired after 43 years at GTE, remaining on the GTE board of directors as chairman Emeritus. Charles "Chuck" Lee was named to succeed Johnson. In 1994, Lee sold the company's satellite provider, Spacenet, to General Electric and Contel of Maine to Oxford Networks, which placed the company into a newly created subsidiary, Oxford West Telephone.

Merger with Bell Atlantic
Bell Atlantic merged with GTE on June 30, 2000, and named the new entity Verizon Communications. The GTE operating companies retained by Verizon are now collectively known as Verizon West division of Verizon (including east coast service territories). The remaining smaller operating companies were sold off or transferred into the remaining ones. Additional properties were sold off within a few years after the merger to CenturyTel, Alltel, and Hawaiian Telcom. On July 1, 2010, Verizon sold many former GTE properties to Frontier Communications. Other GTE territories in California, Florida, and Texas were sold to Frontier in 2015 and transferred in 2016, thus ending Verizon's landline operations outside of the historic Bell Atlantic footprint. Verizon still operates phone service in non-Bell System areas in Pennsylvania under Verizon North, and in non-Bell System areas in Virginia and Knotts Island, North Carolina under Verizon South.

Operating companies
Prior to the merger with Bell Atlantic, GTE owned the following operating companies in the US:
 * Contel of Minnesota, Inc.
 * Contel of the South, Inc. (Alabama, Indiana, Michigan)
 * GTE Alaska Incorporated
 * GTE Arkansas Incorporated
 * GTE California Incorporated (Arizona, California, Nevada)
 * GTE Florida Incorporated
 * GTE Hawaiian Telephone Company, Inc.
 * GTE Midwest Incorporated (Iowa, Missouri, Nebraska)
 * GTE North Incorporated (Illinois, Indiana, Michigan, Ohio, Pennsylvania, Wisconsin)
 * GTE Northwest Incorporated (Idaho, Oregon, Washington)
 * GTE South Incorporated (Illinois, Kentucky, North Carolina, South Carolina, Wisconsin)
 * GTE Southwest Incorporated (Arkansas, New Mexico, Oklahoma, Texas)
 * GTE West Coast Incorporated (California)

Following the merger of GTE and Bell Atlantic, some of these companies and/or access lines have been sold off to other companies, such as Alltel, ATEAC, The Carlyle Group, CenturyTel, Citizens/Frontier Communications, and Valor Telecom.

title: GTE


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General aviation

General aviation (GA) is defined by the International Civil Aviation Organization (ICAO) as all civil aviation aircraft operations except for commercial air transport or aerial work, which is defined as specialized aviation services for other purposes. However, for statistical purposes, ICAO uses a definition of general aviation which includes aerial work.

General aviation thus represents the "private transport" and recreational components of aviation, most of which is accomplished with light aircraft.

Definition

The International Civil Aviation Organization (ICAO) defines civil aviation aircraft operations in three categories: General Aviation (GA), Aerial Work (AW) and Commercial Air Transport (CAT). Aerial work operations are separated from general aviation by ICAO by this definition. Aerial work is when an aircraft is used for specialized services such as agriculture, construction, photography, surveying, observation and patrol, search and rescue, and aerial advertisement. However, for statistical purposes ICAO includes aerial work within general aviation, and has proposed officially extending the definition of general aviation to include aerial work, to reflect common usage. The proposed ICAO classification includes instructional flying as part of general aviation (non-aerial-work).

The International Council of Aircraft Owner and Pilot Associations (IAOPA) refers to the category as general aviation/aerial work (GA/AW) to avoid ambiguity. Their definition of general aviation includes:

 * Corporate aviation: company own-use flight operations
 * Fractional ownership operations: aircraft operated by a specialized company on behalf of two or more co-owners
 * Business aviation (or travel): self-flown for business purposes
 * Personal/private travel: travel for personal reasons/personal transport
 * Air tourism: self-flown incoming/outgoing tourism
 * Recreational flying: powered/powerless leisure flying activities
 * Air sports: aerobatics, air races, competitions, rallies, etc.

General aviation thus includes both commercial and non-commercial activities.

IAOPA's definition of aerial work includes, but is not limited to:

 * Agricultural flights, including crop dusting
 * Banner towing
 * Aerial firefighting
 * Medical evacuation
 * Pilot training
 * Search and rescue
 * Sight seeing flights
 * Skydiving flights
 * Organ transplant transport flights

Commercial air transport includes:

 * Scheduled air services
 * Non-scheduled air transport
 * Air cargo services
 * Air taxi operations

However, in some countries, air taxi is regarded as being part of GA/AW.

Private flights are made in a wide variety of aircraft: light and ultra-light aircraft, sport aircraft, homebuilt aircraft, business aircraft (like private jets), gliders and helicopters. Flights can be carried out under both visual flight and instrument flight rules, and can use controlled airspace with permission.

The majority of the world's air traffic falls into the category of general aviation, and most of the world's airports serve GA exclusively. Flying clubs are considered a part of general aviation.

Europe
In 2003, the European Aviation Safety Agency was established as the central EU regulator, taking over responsibility for legislating airworthiness and environmental regulation from the national authorities.

United Kingdom
Of the 21,000 civil aircraft registered in the United Kingdom, 96 percent are engaged in GA operations, and annually the GA fleet accounts for between 1.25 and 1.35 million hours flown. There are 28,000 private pilot licence holders, and 10,000 certified glider pilots. Some of the 19,000 pilots who hold professional licences are also engaged in GA activities. GA operates from more than 1,800 airports and landing sites or aerodromes, ranging in size from large regional airports to farm strips.

GA is regulated by the Civil Aviation Authority. The main focus is on standards of airworthiness and pilot licensing, and the objective is to promote high standards of safety.

North America
General aviation is particularly popular in North America, with over 6,300 airports available for public use by pilots of general aviation aircraft (around 5,200 airports in the U.S. and over 1,000 in Canada ). In comparison, scheduled flights operate from around 560 airports in the U.S. According to the U.S. Aircraft Owners and Pilots Association, general aviation provides more than one percent of the United States' GDP, accounting for 1.3 million jobs in professional services and manufacturing.

Regulation
Most countries have a civil aviation authority that oversees all civil aviation, including general aviation, adhering to the standardized codes of the International Civil Aviation Organization (ICAO).

Safety
Aviation accident rate statistics are necessarily estimates. According to the U.S. National Transportation Safety Board, general aviation in the United States (excluding charter) suffered 1.31 fatal accidents for every 100,000 hours of flying in 2005, compared to 0.016 for scheduled airline flights. In Canada, recreational flying accounted for 0.7 fatal accidents for every 1000 aircraft, while air taxi accounted for 1.1 fatal accidents for every 100,000 hours. More experienced GA pilots appear generally safer, although the relationship between flight hours, accident frequency, and accident rates are complex and often difficult to assess.

A small number of commercial aviation accidents in the United States have involved collisions with general aviation flights, notably TWA Flight 553, Piedmont Airlines Flight 22, Allegheny Airlines Flight 853, PSA Flight 182 and Aeroméxico Flight 498.

title: General aviation


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Grue

Grue may refer to:

People

 * A pen name used by cartoonist Johnny Gruelle
 * Grue (surname), notable people with the surname Grue

Places

 * Grue, Norway, a municipality in Innlandet county
 * Isle-aux-Grues, an island in Quebec, Canada
 * Grues, Vendée, a commune in France
 * Grue (river), a river in north-west Italy

In fiction

 * Grue (monster), a fictional predatory creature invented by American author Jack Vance and featured in the Zork series of interactive fiction computer games
 * Grue (Freedom City), an alien race in the role-playing game Mutants and Masterminds
 * Grue/Brian Laborn, a supervillain in the web novel Worm

Other

 * Grue and bleen, portmanteau words formed from green and blue, coined by Nelson Goodman to illustrate his new riddle of induction
 * Grue, a linguistic and translation concept (see Blue–green distinction in language)
 * Crane (bird), a bird from the Grue family
 * Grue, an influential science fiction fanzine published by Dean Grennell
 * An early form of Nutraloaf, a food served in prison, known as "grue" to prisoners in the Arkansas penal system as described in the 1978 Hutto v. Finney decision

title: Grue