In computer graphics , the Cohen–Sutherland algorithm is an algorithm used for line clipping . The algorithm divides a two-dimensional space into 9 regions and then efficiently determines the lines and portions of lines that are visible in the central region of interest (the viewport ).
112-424: The algorithm was developed in 1967 during flight simulator work by Danny Cohen and Ivan Sutherland . The algorithm includes, excludes or partially includes the line based on whether: The numbers in the figure below are called outcodes . An outcode is computed for each of the two points in the line. The outcode will have 4 bits for two-dimensional clipping, or 6 bits in the three-dimensional case. The first bit
224-449: A simulation model are the equations of motion for the aircraft. As the aircraft moves through atmosphere it can exhibit both translational and rotational degrees of freedom . To achieve perception of fluent movement, these equations are solved 50 or 60 times per second. The forces for motion are calculated from aerodynamical models, which in turn depend on state of control surfaces, driven by specific systems, with their avionics, etc. As
336-466: A stick shaker . Another form of tactile input from the pilot are instruments located on the panels in the cockpit. As they are used to interact with various aircraft systems, just that may be sufficient for some forms of procedure training. Displaying them on a screen is sufficient for the most basic BITD simulators and amateur flight simulation , however most classes of certified simulators need all buttons, switches and other inputs to be operated in
448-547: A database of known pulsar frequencies and locations. Similar to GNSS, this comparison would allow the vehicle to triangulate its position accurately (±5 km). The advantage of using X-ray signals over radio waves is that X-ray telescopes can be made smaller and lighter. On 9 November 2016 the Chinese Academy of Sciences launched an experimental pulsar navigation satellite called XPNAV 1 . SEXTANT (Station Explorer for X-ray Timing and Navigation Technology)
560-400: A day or two of instruction and practice, even using manual calculation methods. Modern practical navigators usually use celestial navigation in combination with satellite navigation to correct a dead reckoning track, that is, a course estimated from a vessel's position, course, and speed. Using multiple methods helps the navigator detect errors and simplifies procedures. When used this way,
672-520: A day), and 180,000 first officers evolving to captains . The largest manufacturer is Canadian CAE Inc. with a 70% market share and $ 2.8 billion annual revenues, manufacturing training devices for 70 years but moved into training in 2000 with multiple acquisitions. Now CAE makes more from training than from producing the simulators. Crawley-based L3 CTS entered the market in 2012 by acquiring Thales Training & Simulation 's manufacturing plant near Gatwick Airport where it assembles up to 30 devices
784-581: A dozen Army pilots were killed. The Army Air Force hierarchy remembered Ed Link and his trainer. Link flew in to meet them at Newark Field in New Jersey, and they were impressed by his ability to arrive on a day with poor visibility, due to practice on his training device. The result was that the USAAF purchased six Link Trainers, and this can be said to mark the start of the world flight simulation industry. The principal pilot trainer used during World War II
896-476: A flat surface, as well as brightness in regions with overlapping projections. There are also different shapes of screens used, including cylindrical, spherical or ellipsoidal. The image can be projected on the viewing side of the projection screen , or alternatively "back-projection" onto a translucent screen. Because the screen is much closer than objects outside aircraft, the most advanced flight simulators employ cross-cockpit collimated displays that eliminate
1008-402: A horizontal beam on which are mounted 40 ft rails, allowing lateral movement of a simulator cab of +/- 20 feet. A conventional 6-degree of freedom hexapod platform is mounted on the 40 ft beam, and an interchangeable cabin is mounted on the platform. This design permits quick switching of different aircraft cabins. Simulations have ranged from blimps, commercial and military aircraft to
1120-425: A limit on maximum latency between pilot input and aircraft reaction. Because of that, tradeoffs are made to reach the required level of realism with a lower computational cost. Flight simulators typically don't include full computational fluid dynamics models for forces or weather, but use databases of prepared results from calculations and data acquired in real flights. As an example, instead of simulating flow over
1232-401: A method of determining time at the prime meridian. A functioning timepiece with a second hand or digit, an almanac with lunar corrections, and a sextant are used. With no knowledge of time at all, a lunar calculation (given an observable Moon of respectable altitude) can provide time accurate to within a second or two with about 15 to 30 minutes of observations and mathematical reduction from
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#17327902035211344-411: A military aircraft or hoist operators. Separate simulators have also been used for tasks related to flight, like evacuating the aircraft in case of a crash in water. With high complexity of many systems composing contemporary aircraft, aircraft maintenance simulators are increasingly popular. Before September 2018, when a manufacturer wished to have an ATD model approved, a document that contains
1456-441: A moving platform under fair conditions, can achieve a practical accuracy of approximately 1.5 nautical miles (2.8 km, enough to navigate safely when out of sight of land or other hazards. Practical celestial navigation usually requires a marine chronometer to measure time, a sextant to measure the angles, an almanac giving schedules of the coordinates of celestial objects, a set of sight reduction tables to help perform
1568-439: A navigator checked their chronometer(s) with their sextant at a geographic marker surveyed by a professional astronomer. This is now a rare skill, and most harbormasters cannot locate their harbor's marker. Ships often carried more than one chronometer. Chronometers were kept on gimbals in a dry room near the center of the ship. They were used to set a hack watch for the actual sight, so that no chronometers were ever exposed to
1680-449: A navigator, from time to time, measures the Sun's altitude with a sextant, then compares that with a precalculated altitude based on the exact time and estimated position of the observation. On the chart, the straight edge of a plotter can mark each position line. If the position line indicates a location more than a few miles from the estimated position, more observations can be taken to restart
1792-430: A pilot license. Specific classes of simulators are also used for training other than obtaining initial license such as instrument rating revalidation, or most commonly obtaining type rating for specific kind of aircraft. During the aircraft design process , flight simulators can be used instead of performing some flight tests. Such "engineering flight simulators" can provide a fast way to find errors, reducing both
1904-571: A prudent mariner never relies on any sole means of fixing their position, many national maritime authorities still require deck officers to show knowledge of celestial navigation in examinations, primarily as a backup for electronic or satellite navigation. One of the most common current uses of celestial navigation aboard large merchant vessels is for compass calibration and error checking at sea when no terrestrial references are available. In 1980, French Navy regulations still required an independently operated timepiece on board so that, in combination with
2016-650: A range of simulators for disorientation training, that have full freedom in yaw. The most complex of these devices is the Desdemona simulator at the TNO Research Institute in The Netherlands, manufactured by AMST. This large simulator has a gimballed cockpit mounted on a framework which adds vertical motion. The framework is mounted on rails attached to a rotating platform. The rails allow the simulator cab to be positioned at different radii from
2128-482: A screen Flight Navigation and Procedures Trainer (FNPT) : Representation of cockpit with all equipment and software to replicate function of aircraft systems Flight Training Devices (FTD) Full Flight Simulators (FFS) Flight simulators are an example of a human-in-the-loop system, in which interaction with a human user is constantly happening. From perspective of the device, the inputs are primary flight controls , instrument panel buttons and switches and
2240-420: A self-contained system with well-defined inputs and outputs. All classes of FSTD require some form of replicating the cockpit. As they are the primary means of interaction between the pilot and the aircraft special importance is assigned to cockpit controls . To achieve good transfer of skills, there are very specific requirements in the flight simulator regulations that determine how closely they must match
2352-415: A sextant, a ship's position could be determined by celestial navigation. The U.S. Air Force and U.S. Navy continued instructing military aviators on celestial navigation use until 1997, because: The United States Naval Academy (USNA) announced that it was discontinuing its course on celestial navigation (considered to be one of its most demanding non-engineering courses) from the formal curriculum in
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#17327902035212464-459: A similar measurement of a star near the eastern or western horizons would provide the longitude . The problem is that the Earth turns 15 degrees per hour, making such measurements dependent on time. A measure a few minutes before or after the same measure the day before creates serious navigation errors. Before good chronometers were available, longitude measurements were based on the transit of
2576-410: A single observation of the exact altitude of the Sun and the exact time of that altitude (known as "local noon")—the highest point of the Sun above the horizon from the position of the observer in any single day. This angular observation, combined with knowing its simultaneous precise time, referred to as the time at the prime meridian, directly renders a latitude and longitude fix at the time and place of
2688-503: A structured test schedule. For many years, it was believed that 6 DOF motion-based simulation gave the pilot closer fidelity to flight control operations and aircraft responses to control inputs and external forces and gave a better training outcome for students than non-motion-based simulation. This is described as "handling fidelity", which can be assessed by test flight standards such as the numerical Cooper-Harper rating scale for handling qualities. Recent scientific studies have shown that
2800-410: A tilting ship, or indeed a moving vehicle of any kind). Two useful methods evolved during the 18th century and are still practiced today: lunar distance , which does not involve the use of a chronometer, and the use of an accurate timepiece or chronometer. Presently, layperson calculations of longitude can be made by noting the exact local time (leaving out any reference for daylight saving time ) when
2912-592: A triangle where the exact position is inside of it. The accuracy of the sights is indicated by the size of the triangle. Joshua Slocum used both noon sight and star sight navigation to determine his current position during his voyage, the first recorded single-handed circumnavigation of the world. In addition, he used the lunar distance method (or "lunars") to determine and maintain known time at Greenwich (the prime meridian), thereby keeping his "tin clock" reasonably accurate and therefore his position fixes accurate. Celestial navigation can only determine longitude when
3024-530: A year, then UK CTC training school in 2015, Aerosim in Sanford, Florida in 2016, and Portuguese academy G Air in October 2017. With a 20% market share, equipment still accounts for more than half of L3 CTS turnover but that could soon be reversed as it educates 1,600 commercial pilots each year, 7% of the 22,000 entering the profession annually, and aims for 10% in a fragmented market. The third largest
3136-708: A year: 85% FFSs and 15% FTD s. CAE supplied 56% of this installed base, L3 CTS 20% and FlightSafety International 10%, while CAE's training centres are the largest operator, with a 13% share. North America has 38% of the world's training devices, Asia-Pacific 25% and Europe 24%. Boeing types represent 45% of all simulated aircraft, followed by Airbus with 35%, then Embraer at 7%, Bombardier at 6% and ATR at 3%. Most flight simulators are used primarily for flight training . The simplest simulators are used to practice basic cockpit procedures, such as processing emergency checklists, and for cockpit familiarization. They are also used for instrument flight training, for which
3248-620: Is TRU Simulation + Training , created in 2014 when parent Textron Aviation merged its simulators with Mechtronix , OPINICUS and ProFlight , focusing on simulators and developing the first full-flight simulators for the 737 MAX and the 777X . The fourth is FlightSafety International , focused on general , business and regional aircraft . Airbus and Boeing have invested in their own training centres, aiming for higher margins than aircraft manufacturing like MRO , competing with their suppliers CAE and L3. In June 2018, there were 1,270 commercial airline simulators in service, up by 50 over
3360-677: Is a NASA -funded project developed at the Goddard Space Flight Center that is testing XNAV on-orbit on board the International Space Station in connection with the NICER project, launched on 3 June 2017 on the SpaceX CRS-11 ISS resupply mission. Celestial navigation training equipment for aircraft crews combine a simple flight simulator with a planetarium . An early example
3472-410: Is directly related to the distance between the celestial body's GP and the observer's position. After some computations, referred to as " sight reduction," this measurement is used to plot a line of position (LOP) on a navigational chart or plotting worksheet, with the observer's position being somewhere on that line. The LOP is actually a short segment of a very large circle on Earth that surrounds
Cohen–Sutherland algorithm - Misplaced Pages Continue
3584-410: Is known as "parallel simulation" or "distributed simulation". As military aircraft often need to cooperate with other craft or military personnel, wargames are a common use for distributed simulation. Because of that, numerous standards for distributed simulation including aircraft have been developed with military organisations. Some examples include SIMNET , DIS and HLA . The central element of
3696-515: Is performed without using satellite navigation or other similar modern electronic or digital positioning means. Celestial navigation uses "sights," or timed angular measurements, taken typically between a celestial body (e.g., the Sun , the Moon , a planet , or a star ) and the visible horizon . Celestial navigation can also take advantage of measurements between celestial bodies without reference to
3808-438: Is reliable, offshore yachtsmen use celestial navigation as either a primary navigational tool or as a backup. Celestial navigation was used in commercial aviation up until the early part of the jet age; early Boeing 747s had a "sextant port" in the roof of the cockpit. It was only phased out in the 1960s with the advent of inertial navigation and Doppler navigation systems, and today's satellite-based systems which can locate
3920-406: Is set to 1 if the point is above the viewport. The bits in the 2D outcode represent: top, bottom, right, left. For example, the outcode 1010 represents a point that is top-right of the viewport. Note that the outcodes for endpoints must be recalculated on each iteration after the clipping occurs. The Cohen–Sutherland algorithm can be used only on a rectangular clip window . Algorithms used for
4032-604: Is the Link Celestial Navigation Trainer , used in the Second World War . Housed in a 45-foot (14 m) high building, it featured a cockpit accommodating a whole bomber crew (pilot, navigator, and bombardier). The cockpit offered a full array of instruments , which the pilot used to fly the simulated airplane. Fixed to a dome above the cockpit was an arrangement of lights, some collimated , simulating constellations , from which
4144-472: Is the case with modelling, depending on the required level of realism, there are different levels of detail, with some sub-models omitted in simpler simulators. If a human user is part of the simulator, which might not be the case for some engineering simulators, there is a need to perform the simulation in real-time. Low refresh rates not only reduce realism of simulation, but they have also been linked with increase in simulator sickness . The regulations place
4256-401: Is used for a variety of reasons, including flight training (mainly of pilots), the design and development of the aircraft itself, and research into aircraft characteristics and control handling qualities. The term "flight simulator" may carry slightly different meaning in general language and technical documents. In past regulations, it referred specifically to devices which can closely mimic
4368-470: The Merchant Marine . It is also taught at Harvard , most recently as Astronomy 2. Celestial navigation continues to be used by private yachtsmen, and particularly by long-distance cruising yachts around the world. For small cruising boat crews, celestial navigation is generally considered an essential skill when venturing beyond visual range of land. Although satellite navigation technology
4480-408: The celestial north pole . If a navigator measures the angle to Polaris and finds it to be 10 degrees from the horizon, then he is about 10 degrees north of the equator. This approximate latitude is then corrected using simple tables or almanac corrections to determine a latitude that is theoretically accurate to within a fraction of a mile. Angles are measured from the horizon because locating
4592-432: The parallax effect between the pilots' point of view, and provide a more realistic view of distant objects. An alternative to large-scale displays are virtual reality simulators using a head-mounted display . This approach allows for a complete field of view, and makes the simulator size considerably smaller. There are examples of use in research, as well as certified FSTD . Visual simulation science applied from
Cohen–Sutherland algorithm - Misplaced Pages Continue
4704-471: The "Link Trainer". Link also demonstrated his trainer to the U.S. Army Air Force (USAAF), but with no result. However, the situation changed in 1934 when the Army Air Force was given a government contract to fly the postal mail. This included having to fly in bad weather as well as good, for which the USAAF had not previously carried out much training. During the first weeks of the mail service, nearly
4816-401: The "Zero Meridian" at Greenwich, also known as UTC or GMT). Knowing UTC/GMT, a further set of sights can be taken and reduced by the navigator to calculate their exact position on the Earth as a local latitude and longitude. The considerably more popular method was (and still is) to use an accurate timepiece to directly measure the time of a sextant sight. The need for accurate navigation led to
4928-427: The Earth's atmosphere . The immunity to jamming signals is the main driver behind this seemingly archaic technique. X-ray pulsar-based navigation and timing (XNAV) is an experimental navigation technique for space whereby the periodic X-ray signals emitted from pulsars are used to determine the location of a vehicle, such as a spacecraft in deep space. A vehicle using XNAV would compare received X-ray signals with
5040-502: The Earth's horizon, such as when the Moon and other selected bodies are used in the practice called "lunars" or the lunar distance method , used for determining precise time when time is unknown. Celestial navigation by taking sights of the Sun and the horizon whilst on the surface of the Earth is commonly used, providing various methods of determining position, one of which is the popular and simple method called "noon sight navigation"—being
5152-593: The Earth, whether on land, in the air, or at sea. In addition, observations between stars and other celestial bodies accomplished the same results while in space, – used in the Apollo space program and is still used on many contemporary satellites. Equally, celestial navigation may be used while on other planetary bodies to determine position on their surface, using their local horizon and suitable celestial bodies with matching reduction tables and knowledge of local time. For navigation by celestial means, when on
5264-519: The French commanders Clolus and Laffont and Lieutenant Clavenad, the first ground training aircraft for military aircraft were built. The "Tonneau Antoinette" (Antoinette barrel), created by the Antoinette company, seems to be the precursor of flight simulators. An area of training was for air gunnery handled by the pilot or a specialist air gunner. Firing at a moving target requires aiming ahead of
5376-596: The GP of the observed celestial body. (An observer located anywhere on the circumference of this circle on Earth, measuring the angle of the same celestial body above the horizon at that instant of time, would observe that body to be at the same angle above the horizon.) Sights on two celestial bodies give two such lines on the chart, intersecting at the observer's position (actually, the two circles would result in two points of intersection arising from sights on two stars described above, but one can be discarded since it will be far from
5488-458: The Moon at the left of the Sun, and an observer at the Madeira point would see the Moon at the right of the Sun. Accurate angle measurement has evolved over the years. One simple method is to hold the hand above the horizon with one's arm stretched out. The angular width of the little finger is just over 1.5 degrees at extended arm's length and can be used to estimate the elevation of the Sun from
5600-649: The QTGs will be rerun during the year to prove during continuous qualification that the simulator is still in the tolerances approved by the CAA. These definitions apply to both airplanes and helicopters unless specified otherwise. Training devices briefly compared below are all different subclasses of Flight simulation training device (FSTD). Basic instrument training device (BITD) airplanes only : A basic student station for instrument flight procedures; can use spring loaded flight controls, and instruments displayed on
5712-533: The Singer Link Digital Image Generator (DIG) created in 1978 was considered one of the worlds first CGI system. Initially, the motion systems used separate axes of movement, similar to a gimbal . After the invention of Stewart platform simultaneous operation of all actuators became the preferred choice, with some FFS regulations specifically requiring "synergistic" 6 degrees of freedom motion. In contrast to real aircraft,
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#17327902035215824-680: The Space Shuttle. In the case of the Space Shuttle, the large Vertical Motion Simulator was used to investigate a longitudinal pilot-induced oscillation (PIO) that occurred on an early Shuttle flight just before landing. After identification of the problem on the VMS, it was used to try different longitudinal control algorithms and recommend the best for use in the Shuttle program. AMST Systemtechnik GmbH (AMST) of Austria and Environmental Tectonics Corporation (ETC) of Philadelphia, US, manufacture
5936-559: The Sun and Moon were observed at their respective angles from the same location, the navigator would have to be located at one of the two locations where the circles cross. In this case, the navigator is either located on the Atlantic Ocean, about 350 nautical miles (650 km) west of Madeira , or in South America, about 90 nautical miles (170 km) southwest of Asunción , Paraguay. In most cases, determining which of
6048-488: The Sun is at its highest point in Earth's sky. The calculation of noon can be made more easily and accurately with a small, exactly vertical rod driven into level ground—take the time reading when the shadow is pointing due north (in the northern hemisphere). Then take your local time reading and subtract it from GMT ( Greenwich Mean Time), or the time in London, England. For example, a noon reading (12:00) near central Canada or
6160-580: The US would occur at approximately 6 p.m. (18:00) in London. The 6-hour difference is one quarter of a 24-hour day, or 90 degrees of a 360-degree circle (the Earth). The calculation can also be made by taking the number of hours (use decimals for fractions of an hour) multiplied by 15, the number of degrees in one hour. Either way, it can be demonstrated that much of central North America is at or near 90 degrees west longitude. Eastern longitudes can be determined by adding
6272-402: The adjacent image, the two circles on the map represent lines of position for the Sun and Moon at 12:00 GMT on October 29, 2005. At this time, a navigator on a ship at sea measured the Moon to be 56° above the horizon using a sextant . Ten minutes later, the Sun was observed to be 40° above the horizon. Lines of position were then calculated and plotted for each of these observations. Since both
6384-447: The aircraft is an important cue for flying the aircraft, and is the primary means of navigation for visual flight rules operation. One of the primary characteristics of a visual system is the field of view . Depending on the simulator type it may be sufficient to provide only a view forward using a flat display. However, some types of craft, e.g. fighter aircraft , require a very large field of view, preferably almost full sphere, due to
6496-728: The aircraft's position accurate to a 3-meter sphere with several updates per second. A variation on terrestrial celestial navigation was used to help orient the Apollo spacecraft en route to and from the Moon. To this day, space missions such as the Mars Exploration Rover use star trackers to determine the attitude of the spacecraft. As early as the mid-1960s, advanced electronic and computer systems had evolved enabling navigators to obtain automated celestial sight fixes. These systems were used aboard both ships and US Air Force aircraft, and were highly accurate, able to lock onto up to 11 stars (even in daytime) and resolve
6608-478: The almanac tables. After practice, an observer can regularly derive and prove time using this method to within about one second, or one nautical mile, of navigational error due to errors ascribed to the time source. An example illustrating the concept behind the intercept method for determining position is shown to the right. (Two other common methods for determining one's position using celestial navigation are longitude by chronometer and ex-meridian methods.) In
6720-480: The altitude of the Sun at noon (the "noon sight") or by measuring the altitudes of any other celestial body when crossing the meridian (reaching its maximum altitude when due north or south), and frequently by measuring the altitude of Polaris , the north star (assuming it is sufficiently visible above the horizon, which it is not in the Southern Hemisphere ). Polaris always stays within 1 degree of
6832-563: The angle between the Moon and the Sun or between the Moon and one of several stars near the ecliptic . The observed angle must be corrected for the effects of refraction and parallax, like any celestial sight. To make this correction, the navigator measures the altitudes of the Moon and Sun (or another star) at about the same time as the lunar distance angle. Only rough values for the altitudes are required. A calculation with suitable published tables (or longhand with logarithms and graphical tables) requires about 10 to 15 minutes' work to convert
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#17327902035216944-419: The average vessel at sea. Although most recently only used by sextant hobbyists and historians, it is now becoming more common in celestial navigation courses to reduce total dependence on GNSS systems as potentially the only accurate time source aboard a vessel. Designed for use when an accurate timepiece is not available or timepiece accuracy is suspect during a long sea voyage, the navigator precisely measures
7056-415: The behavior of aircraft throughout various procedures and flight conditions. In more recent definitions, this has been named " full flight simulator ". The more generic term "flight simulation training device" (FSTD) is used to refer to different kinds of flight training devices, and that corresponds more closely to meaning of the phrase "flight simulator" in general English. In 1910, on the initiative of
7168-524: The bomber to practice lining up bombing targets. A team of operators sat at a control booth on the ground below the machine, from which they could simulate weather conditions such as wind or clouds. This team also tracked the airplane's position by moving a "crab" (a marker) on a paper map. The Link Celestial Navigation Trainer was developed in response to a request made by the Royal Air Force (RAF) in 1939. The RAF ordered 60 of these machines, and
7280-496: The centre of rotation and this gives a sustained G capability up to about 3.5. Celestial Navigation Celestial navigation , also known as astronavigation , is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the surface of the Earth without relying solely on estimated positional calculations, commonly known as dead reckoning . Celestial navigation
7392-447: The concept illustrated in the example in the "How it works" section above.) Two other methods of reducing sights are the longitude by chronometer and the ex-meridian method. While celestial navigation is becoming increasingly redundant with the advent of inexpensive and highly accurate satellite navigation receivers ( GNSS ), it was used extensively in aviation until the 1960s and marine navigation until quite recently. However, since
7504-524: The craft's position to less than 300 feet (91 m). The SR-71 high-speed reconnaissance aircraft was one example of an aircraft that used a combination of automated celestial and inertial navigation . These rare systems were expensive, however, and the few that remain in use today are regarded as backups to more reliable satellite positioning systems. Intercontinental ballistic missiles use celestial navigation to check and correct their course (initially set using internal gyroscopes) while flying outside
7616-400: The dead-reckoning track. In the event of equipment or electrical failure, taking Sun lines a few times a day and advancing them by dead reckoning allows a vessel to get a crude running fix sufficient to return to port. One can also use the Moon, a planet, Polaris , or one of 57 other navigational stars to track celestial positioning. Latitude was measured in the past either by measuring
7728-461: The development of progressively more accurate chronometers in the 18th century (see John Harrison ). Today, time is measured with a chronometer, a quartz watch , a shortwave radio time signal broadcast from an atomic clock , or the time displayed on a satellite time signal receiver. A quartz wristwatch normally keeps time within a half-second per day. If it is worn constantly, keeping it near body heat, its rate of drift can be measured with
7840-400: The development of the modern (Marcq St. Hilaire) intercept method ; with this method, the body height and azimuth are calculated for a convenient trial position and compared with the observed height. The difference in arcminutes is the nautical mile "intercept" distance that the position line needs to be shifted toward or away from the direction of the body's subpoint. (The intercept method uses
7952-436: The estimated position—see the figure at the example below). Most navigators will use sights of three to five stars, if available, since that will result in only one common intersection and minimize the chance of error. That premise is the basis for the most commonly used method of celestial navigation, referred to as the "altitude-intercept method." At least three points must be plotted. The plot intersection will usually provide
8064-418: The height and azimuth computations, and a chart of the region. With sight reduction tables, the only calculations required are addition and subtraction. Small handheld computers, laptops and even scientific calculators enable modern navigators to "reduce" sextant sights in minutes, by automating all the calculation and/or data lookup steps. Most people can master simpler celestial navigation procedures after
8176-461: The horizon plane and therefore estimate the time until sunset. The need for more accurate measurements led to the development of a number of increasingly accurate instruments, including the kamal , astrolabe , octant , and sextant . The sextant and octant are most accurate because they measure angles from the horizon, eliminating errors caused by the placement of an instrument's pointers, and because their dual-mirror system cancels relative motions of
8288-445: The instructor's station, if present. Based on these, the internal state is updated, and equations of motion solved for the new time step. The new state of the simulated aircraft is shown to the user through visual, auditory, motion and touch channels. To simulate cooperative tasks, the simulator can be suited for multiple users, as is the case with multi-crew cooperation simulators. Alternatively, more simulators can be connected, what
8400-502: The instrument, showing a steady view of the object and horizon. Navigators measure distance on the Earth in degrees , arcminutes , and arcseconds . A nautical mile is defined as 1,852 meters but is also (not accidentally) one arc minute of angle along a meridian on the Earth. Sextants can be read accurately to within 0.1 arcminutes, so the observer's position can be determined within (theoretically) 0.1 nautical miles (185.2 meters, or about 203 yards. Most ocean navigators, measuring from
8512-479: The local time to GMT, with similar calculations. An older but still useful and practical method of determining accurate time at sea before the advent of precise timekeeping and satellite-based time systems is called " lunar distances," or "lunars," which was used extensively for a short period and refined for daily use on board ships in the 18th century. Use declined through the middle of the 19th century as better and better timepieces (chronometers) became available to
8624-494: The manoeuvres that are performed during air combat. Similarly, since helicopters can perform hover flight in any direction, some classes of helicopter flight simulators require even 180 degrees of horizontal field of view. There are many parameters in visual system design. For a narrow field of view, a single display may be sufficient, however typically multiple projectors are required. This arrangement needs additional calibration, both in terms of distortion from not projecting on
8736-423: The moon or the positions of the moons of Jupiter . For the most part, these were too difficult to be used by anyone except professional astronomers. The invention of the modern chronometer by John Harrison in 1761 vastly simplified longitudinal calculation. The longitude problem took centuries to solve and was dependent on the construction of a non-pendulum clock (as pendulum clocks cannot function accurately on
8848-425: The navigator determined the plane's position. The dome's movement simulated the changing positions of the stars with the passage of time and the movement of the plane around the Earth. The navigator also received simulated radio signals from various positions on the ground. Below the cockpit moved "terrain plates"—large, movable aerial photographs of the land below—which gave the crew the impression of flight and enabled
8960-409: The observation by simple mathematical reduction. The Moon, a planet, Polaris , or one of the 57 other navigational stars whose coordinates are tabulated in any of the published nautical or air almanacs can also accomplish this same goal. Celestial navigation accomplishes its purpose by using angular measurements (sights) between celestial bodies and the visible horizon to locate one's position on
9072-401: The observed angle(s) to a geocentric lunar distance. The navigator then compares the corrected angle against those listed in the appropriate almanac pages for every three hours of Greenwich time, using interpolation tables to derive intermediate values. The result is a difference in time between the time source (of unknown time) used for the observations and the actual prime meridian time (that of
9184-460: The outside view is less important. Certain aircraft systems may or may not be simulated, and the aerodynamic model is usually extremely generic if present at all. Depending on the level of certification, instruments that would have moving indicators in a real aircraft may be implemented with a display. With more advanced displays, cockpit representation and motion systems, flight simulators can be used to credit different amount of flight hours towards
9296-433: The platform, providing yaw cues. A generic replica cockpit with working instruments was mounted on the motion platform. When the cockpit was covered, pilots could practice flying by instruments in a safe environment. The motion platform gave the pilot cues as to real angular motion in pitch (nose up and down), roll (wing up or down) and yaw (nose left and right). Initially, aviation flight schools showed little interest in
9408-426: The point directly overhead, the zenith , is not normally possible. When haze obscures the horizon, navigators use artificial horizons, which are horizontal mirrors or pans of reflective fluid, especially mercury. In the latter case, the angle between the reflected image in the mirror and the actual image of the object in the sky is exactly twice the required altitude. If the angle to Polaris can be accurately measured,
9520-423: The radio, and by compensating for this drift, a navigator can keep time to better than a second per month. When time at the prime meridian (or another starting point) is accurately known, celestial navigation can determine longitude, and the more accurately latitude and time are known, the more accurate the longitude determination. The angular speed of the Earth is latitude-dependent. At the poles, or latitude 90°,
9632-574: The real aircraft. These requirements in case of full flight simulators are so detailed, that it may be cost-effective to use the real part certified to fly, rather than manufacture a dedicated replica. Lower classes of simulators may use springs to mimic forces felt when moving the controls. When there is a need to better replicate the control forces or dynamic response, many simulators are equipped with actively driven force feedback systems. Vibration actuators may also be included, either due to helicopter simulation requirements, or for aircraft equipped with
9744-424: The risks and the cost of development. Additionally, this allows use of extra measurement equipment that might be too large or otherwise impractical to include during onboard a real aircraft. Throughout different phases of the design process, different engineering simulators with various level of complexity are used. Flight simulators may include training tasks for crew other than pilots. Examples include gunners on
9856-408: The rotation velocity of the Earth reaches zero. At 45° latitude, one second of time is equivalent in longitude to 1,077.8 ft (328.51 m ), or one-tenth of a second means 107.8 ft (32.86 m) At the slightly bulged-out equator, or latitude 0°, the rotation velocity of Earth or its equivalent in longitude reaches its maximum at 465.10 m/s (1,525.9 ft/s ). Traditionally,
9968-517: The same purpose: Flight simulator A flight simulator is a device that artificially re-creates aircraft flight and the environment in which it flies, for pilot training, design, or other purposes. It includes replicating the equations that govern how aircraft fly, how they react to applications of flight controls, the effects of other aircraft systems, and how the aircraft reacts to external factors such as air density , turbulence , wind shear, cloud, precipitation, etc. Flight simulation
10080-400: The same way as in the aircraft cockpit. The necessity for a physical copy of a cockpit contributes to the cost of simulator construction, and ties the hardware to a specific aircraft type. Because of these reasons, there is ongoing research on interactions in virtual reality , however lack of tactile feedback negatively affects users' performance when using this technology. Outside view from
10192-689: The simulated motion system has a limited range in which it is able to move. That especially affects the ability to simulate sustained accelerations, and requires a separate model to approximate the cues to the human vestibular system within the given constraints. Motion system is a major contributor to overall simulator cost , but assessments of skill transfer based on training on a simulator and leading to handling an actual aircraft are difficult to make, particularly where motion cues are concerned. Large samples of pilot opinion are required and many subjective opinions tend to be aired, particularly by pilots not used to making objective assessments and responding to
10304-515: The specifications for the model line and that proves compliance with the appropriate regulations is submitted to the FAA. Once this document, called a Qualification Approval Guide (QAG), has been approved, all future devices conforming to the QAG are automatically approved and individual evaluation is neither required nor available. The actual procedure accepted by all CAAs (Civil Aviation Authorities) around
10416-635: The spring of 1998. In October 2015, citing concerns about the reliability of GNSS systems in the face of potential hostile hacking , the USNA reinstated instruction in celestial navigation in the 2015 to 2016 academic year. At another federal service academy, the US Merchant Marine Academy, there was no break in instruction in celestial navigation as it is required to pass the US Coast Guard License Exam to enter
10528-410: The surface of the Earth at any given instant in time, a celestial body is located directly over a single point on the Earth's surface. The latitude and longitude of that point are known as the celestial body's geographic position (GP), the location of which can be determined from tables in the nautical or air almanac for that year. The measured angle between the celestial body and the visible horizon
10640-564: The surfaces and transition from one level of image detail to the next one in a smooth manner. Real-time computer graphics visualization of virtual worlds makes some aspects of flight simulator visual systems very similar to game engines , sharing some techniques like different levels of details or libraries like OpenGL . Many computer graphics visionaries began their careers at Evans & Sutherland and Link Flight Simulation, Division of Singer Company, two leading companies in flight simulation before today's modern computing era. For example,
10752-699: The target (which involves the so-called lead angle) to allow for the time the bullets require to reach the vicinity of the target. This is sometimes also called "deflection shooting" and requires skill and practice. During World War I , some ground-based simulators were developed to teach this skill to new pilots. The best-known early flight simulation device was the Link Trainer , produced by Edwin Link in Binghamton, New York , United States, which he started building in 1927. He later patented his design, which
10864-426: The time at the prime meridian is accurately known. The more accurately time at the prime meridian (0° longitude) is known, the more accurate the fix; – indeed, every four seconds of time source (commonly a chronometer or, in aircraft, an accurate " hack watch ") error can lead to a positional error of one nautical mile . When time is unknown or not trusted, the lunar distance method can be used as
10976-408: The two displayed a different time, since in case of contradiction between the two chronometers, it would be impossible to know which one was wrong (the error detection obtained would be the same as having only one chronometer and checking it periodically: every day at noon against dead reckoning ). Three chronometers provided triple modular redundancy , allowing error correction if one of the three
11088-533: The two intersections is the correct one is obvious to the observer because they are often thousands of miles apart. As it is unlikely that the ship is sailing across South America, the position in the Atlantic is the correct one. Note that the lines of position in the figure are distorted because of the map's projection; they would be circular if plotted on a globe. An observer at the Gran Chaco point would see
11200-527: The use of technology such as vibration or dynamic seats within flight simulators can be equally effective in the delivery of training as large and expensive 6-DOF FFS devices. The largest flight simulator in the world is the Vertical Motion Simulator (VMS) at NASA Ames Research Center , south of San Francisco. This has a very large-throw motion system with 60 feet (+/- 30 ft) of vertical movement (heave). The heave system supports
11312-617: The visual systems developed in flight simulators were also an important precursor to three dimensional computer graphics and Computer Generated Imagery (CGI) systems today. Namely because the object of flight simulation is to reproduce on the ground the behavior of an aircraft in flight. Much of this reproduction had to do with believable visual synthesis that mimicked reality. Combined with the need to pair virtual synthesis with military level training requirements, graphics technologies applied in flight simulation were often years ahead of what would have been available in commercial products. When CGI
11424-445: The wind and salt water on deck. Winding and comparing the chronometers was a crucial duty of the navigator. Even today, it is still logged daily in the ship's deck log and reported to the captain before eight bells on the forenoon watch (shipboard noon). Navigators also set the ship's clocks and calendar. Two chronometers provided dual modular redundancy , allowing a backup if one ceases to work but not allowing any error correction if
11536-404: The wings, lift coefficient may be defined in terms of motion parameters like angle of attack . While different models need to exchange data, most often they can be separated into a modular architecture, for better organisation and ease of development. Typically, gear model for ground handling would be separate input to the main equations of motion. Each engine and avionics instrument is also
11648-582: The world is to propose 30 days prior qualification date (40 days for CAAC) a MQTG document (Master Qualification Test Guide), which is proper to a unique simulator device and will live along the device itself, containing objective, and functional and subjective tests to demonstrate the representativeness of the simulator compare to the airplane. The results will be compared to Flight Test Data provided by aircraft OEMs or from test campaign ordered by simulator OEMs or also can be compared by POM (Proof Of Match) data provided by aircraft OEMs development simulators. Some of
11760-400: Was 13.7 m (45 ft) high and capable of accommodating the navigation team of a bomber crew. It enabled sextants to be used for taking "star shots" from a projected display of the night sky. In 1954 United Airlines bought four flight simulators at a cost of $ 3 million from Curtiss-Wright that were similar to the earlier models, with the addition of visuals, sound and movement. This
11872-425: Was also a pilot, but dissatisfied with the amount of real flight training that was available, he decided to build a ground-based device to provide such training without the restrictions of weather and the availability of aircraft and flight instructors. His design had a pneumatic motion platform driven by inflatable bellows which provided pitch and roll cues. A vacuum motor similar to those used in player pianos rotated
11984-414: Was discovered in 1837 by Thomas Hubbard Sumner when, after one observation, he computed and plotted his longitude at more than one trial latitude in his vicinity and noticed that the positions lay along a line. Using this method with two bodies, navigators were finally able to cross two position lines and obtain their position, in effect determining both latitude and longitude. Later in the 19th century came
12096-504: Was first available for sale in 1929. The Link Trainer was a basic metal frame flight simulator usually painted in its well-known blue color. Some of these early war era flight simulators still exist, but it is becoming increasingly difficult to find working examples. The Link family firm in Binghamton manufactured player pianos and organs, and Ed Link was therefore familiar with such components as leather bellows and reed switches. He
12208-514: Was first used to train pilots, early systems proved effective for certain simple training missions but needed further development for sophisticated training tasks as terrain following and other tactical maneuvers. Early CGI systems could depict only objects consisting of planar polygons. Advances in algorithms and electronics in flight simulator visual systems and CGI in the 1970s and 1980s influenced many technologies still used in modern graphics. Over time CGI systems were able to superimpose texture over
12320-561: Was the Link Trainer. Some 10,000 were produced to train 500,000 new pilots from allied nations, many in the US and Canada because many pilots were trained in those countries before returning to Europe or the Pacific to fly combat missions. Almost all US Army Air Force pilots were trained in a Link Trainer. A different type of World War II trainer was used for navigating at night by the stars. The Celestial Navigation Trainer of 1941
12432-527: Was the first of today's modern flight simulators for commercial aircraft. A simulator for helicopters existed as the Jacobs Jaycopter as means of “Cutting helicopter training cost.”. The simulator was later sold as a funfair ride in the 1964-65 New York World's Fair . The simulator manufacturers are consolidating and integrate vertically as training offers double-digit growth: CAE forecast 255,000 new airline pilots from 2017 to 2027 (70
12544-410: Was wrong, so the pilot would take the average of the two with closer readings (average precision vote). There is an old adage to this effect, stating: "Never go to sea with two chronometers; take one or three." Vessels engaged in survey work generally carried many more than three chronometers – for example, HMS Beagle carried 22 chronometers . The celestial line of position concept
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