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Hawk-Eye is a computer system used in cricket, tennis and other sports to visually track the path of the ball and display a record of its actual path as graphic image. In some sports, like tennis, it is now part of the adjudication process. It is also able to predict the future path of a ball. It was developed by engineers at Roke Manor Research Limited of Romsey, Hampshire in the UK, in 2001. A UK patent was submitted by Dr Paul Hawkins and David Sherry. A US, European and Australian patent for ball tracking is held by Auto-Ref Inc. of Toronto, Ontario. Later, the technology was spun off into a separate company, Hawk-Eye Innovations Ltd., as a joint venture with television production company Sunset + Vine.
Method of operation
All Hawk-Eye systems are based on the principles of triangulation using the visual images and timing data provided by at least four high speed video cameras located at different locations and angles around the area of play.  The system rapidly processes the video feeds by a high speed video processor and ball tracker. A data store contains a predefined model of the playing area and includes data on the rules of the game.
In each frame sent from each camera, the system identifies the group of pixels which corresponds to the image of the ball. It then calculates for each frame the 3D position of the ball by comparing its position on at least 2 of the physically separate cameras at the same instant in time. A succession of frames builds up a record of the path along which the ball has traveled. It can also predict, using the laws of physics, the future flight path of the ball and where it will interact with any of the playing area features already programmed into the database. The system can also interpret these interactions to decide infringements of the rules of the game. 
The system generates a graphic image of the ball path and playing area which means that information can be provided to judges, television viewers or coaching staff in near real time.
The pure tracking system is combined with a backend database and archiving capabilities so that it is possible to extract and analyse trends and statistics about individual players, games or ball to ball comparisons etc.
Applications in sport
The technology was first used by Channel 4 during a Test match between England and Pakistan on Lord's Cricket Ground, on 21 May 2001. However, the system is not used by the umpires to adjudicate on LBW decisions in Test cricket or One Day International cricket. It is used primarily by the majority of television networks to track the trajectory of balls in flight.
Its major use in cricket is in analysing leg before wicket decisions, where the likely path of the ball can be projected forward, through the batsman's legs, to see if it would have hit the wicket. Currently this information is only visible to television viewers, although it may be adopted in the future by the third umpire, who currently sees only conventional slow motion replays and can only adjudicate on line decisions (run outs or stumpings) or situations where the on-field umpire's view is impeded. Consultation of the third umpire, for conventional slow motion or hawkeye, on leg before wicket decisions is not currently sanctioned in international cricket and doubts remain about its accuracy in cricket.
Due to its realtime coverage of bowling speed, the systems are also used to show delivery patterns of bowler's behaviour such as line and length, or swing/turn information. At the end of an over, all six deliveries are often shown simultaneously to show a bowler's variations, such as slower deliveries, bouncers and leg-cutters. A complete record of a bowler can also be shown over the course of a match.
Batsmen also benefit from the analysis of Hawk-Eye, as a record can be brought up of the deliveries batsmen scored from. These are often shown as a 2-D silhouetted figure of a batter and colour-coded dots of the balls faced by the batsman or a "wagon wheel" (an aerial view of the batsman's shots all round the ground). Information such as the exact spot where the ball pitches or speed of the ball from the bowler's hand (to gauge batsman reaction time) can also help in post match analysis.
The International Cricket Council (ICC) has now started using both hawk-eye and Auto-Ref technology to assist the decisions made by the umpire. However this is still on a trial status. This was recently introduced in the Test series between India and Sri Lanka (July/August 2008). The ICC is trialling a new "reviewing system" where it makes possible for the players to challenge the decision of umpire. Television umpires can get the assistance of hawk-eye when it comes to LBW decisions.
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Several poor calls occurred at the 2004 US Open. In Serena Williams' quarterfinal loss to Jennifer Capriati, many crucial calls were contested by Williams, and TV replays demonstrated that some were indeed erroneous. Though the calls themselves were not reversed, the chair umpire Mariana Alves was dismissed from the tournament. These errors prompted talks about line calling assistance especially as the Auto-Ref system was being tested by the U.S. Open at that time and was shown to be very accurate.
In late 2005 Hawk-Eye was tested by the International Tennis Federation (ITF) in New York City and was passed for professional use. Hawk-Eye reported that the New York tests involved 80 shots being measured by the ITF's high speed camera, a device similar to MacCAM. These tests have lately been questioned as a single high speed camera would have up to an inch long 'blind spot' and thus cannot measure to mm-level accuracy. The ITF camera was independently measured to be up to 2.9 cm inaccurate, the same camera that supposedly passed Hawkeye in one afternoon of 'testing'. Video based systems are also sensitive to heat and other environmental conditions and a single-day test could not reveal such issues. The Hawk-Eye system has since proved to produce erroneous results at several tournaments, such as in Dubai or at the Australian Open. During an early test of the system during an exhibition tennis tournament in Australia (seen on local TV), there was an instance when the tennis ball was shown as "Out", but the accompanying word was "In". This was explained to be an error in the way the tennis ball was shown on the graphical display as a circle, rather than as an ellipse. This was immediately corrected.
Hawk-Eye has been used in television coverage of several major tennis tournaments, including Wimbledon, the Stella Artois at Queens, the Australian Open, the Davis Cup and the Tennis Masters Cup. The US Open Tennis Championship announced they would make official use of the technology for the 2006 US where each player receives two challenges per set. It is also used as part of a larger tennis simulation implemented by IBM called PointTracker. Along with Cyclops and Auto-Ref, it is one of several automated line-calling mechanisms used.
The 2006 Hopman Cup in Perth, Western Australia, was the first elite-level tennis tournament where players were allowed to challenge point-ending line calls, which were then reviewed by the referees using Hawk-Eye technology. It used 10 cameras feeding information about ball position to the computers.
In March 2006, at the Nasdaq-100 Open, Hawk-Eye was used officially for the first time at a tennis tour event. Later that year, the US Open became the first grand-slam event to use the system during play, allowing players to challenge line calls.
The 2007 Australian Open was the first grand-slam tournament of 2007 to implement Hawk-Eye in challenges to line calls, where each tennis player on Rod Laver Arena was allowed 2 incorrect challenges per set and one additional challenge should a tiebreaker be played. In the event of an advantage final set, challenges are reset to 2 for each player every 12 games i.e. 6 all, 12 all. Controversies followed the event as at times Hawk-Eye produced erroneous output. In 2008, tennis players are allowed 3 incorrect challenges per set instead. Any leftover challenges don't carry over to the next set. Once, in one of Amélie Mauresmo's matches, she challenged a ball that was called in, Hawk-Eye showed the ball was out by less than a millimeter but the verdict was called in. As a result, the point was replayed and Mauresmo didn't lose an incorrect challenge.
The Hawk-Eye technology was used in the 2007 Dubai Tennis Championships with some minor controversies. Defending champion Rafael Nadal accused the system of incorrectly declaring an out ball to be in following his exit. The umpire had called a ball out; when Mikhail Youzhny challenged the decision, Hawk-Eye said it was in. Youzhny said afterwards that he himself thought the mark may have been wide but then offered that this kind of technology error could easily have been made by linesmen and umpires. Nadal could only shrug, saying that had this system been on clay, the mark would have clearly shown Hawk Eye to be wrong.
The 2007 Wimbledon Championships also implemented the Hawk-Eye system as an officiating aid on Centre Court and Court 1, and each tennis player was allowed 3 incorrect challenges per set. If the set produced a tie-breaker, each player was given an additional challenge. Additionally, in the event of a final set (third set in women's or mixed matches, fifth set in men's matches), where there is no tie-break, each player's number of challenges was reset to three if the game score reached 6-6, and again at 12-12. Teimuraz Gabashvili, in his 1st round match against Roger Federer, made the first ever Hawk-Eye challenge on Centre Court. Additionally, during the finals of Federer against Rafael Nadal, Nadal challenged a shot which was called out. Hawk-Eye "proved" it otherwise, with the ball just clipping the line. The reversal agitated Federer enough for him to request (unsuccessfully) that the umpire turn off the Hawk-Eye technology for the remainder of the match.
The Hawk-Eye system was developed as a replay system, originally for TV Broadcast coverage. As such, it cannot call ins and outs live. Currently only the Auto-Ref system can produce live in/out calls as it was developed for instant line calling. Both systems can produce replays.
The Hawk-Eye Innovations website states that the system has an average error of 3.6mm (it does not indicate what the maximum error is). The standard size of a tennis ball is reportedly 65 to 68 mm. This means that there is a 5% error relative to the diameter of the ball. This could throw into doubt the accuracy of such calls as the one mentioned in the Nadal-Federer 2007 Wimbledon final. For the sake of comparison, approximately 5% of the diameter is the fluff on the ball.
Unification of rules
Until March 2008, the International Tennis Federation (ITF), Association of Tennis Professionals (ATP), Women's Tennis Association (WTA), Grand Slam Committee, and several individual tournaments had conflicting rules on how Hawk-Eye was to be utilized. A key example of this was the number of challenges a player was permitted per set, which varied among events. Some tournaments allowed players a greater margin for error, with players allowed an unlimited numbers of challenges over the course of a match. In other tournaments players received two or three per set. On March 19, 2008, the aforementioned organizing bodies announced a uniform system of rules: three unsuccessful challenges per set, with an additional challenge if the set reaches a tie-break. The next scheduled event on the men and women's tour, the 2008 Sony Ericsson Open, was the first event to implement these new, standardized rules.
At the World Snooker Championship 2007 and 2008, the BBC used Hawk-Eye in its television coverage to show player views, particularly in the incidents of potential snookers. It has also been used to demonstrate intended shots by players when the actual shot has gone away.
The BBC continued to use the system sporadically, for instance in the 2009 Masters from Wembley Hawkeye was used once or twice per frame, a most. It was generally used to switch seamlessly from matching a live camera view then swinging the virtual camera to examine a tricky shot from the players' viewpoint.
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On June 14, 2006, it was announced that the Wisden group had bought Hawk-Eye. The acquisition is intended to strengthen Wisden's presence in cricket, and allow it to enter tennis and other international sports. Hawk-Eye is already working on implementing a system for basketball.
According to Hawk-Eye's website, the system produces much more data than that shown on television. This data could easily be shown on the Internet.
The Football Association has declared the system as "ready for inspection by FIFA", after tests suggested that the results of a goal-line incident could be relayed to the match referee within half-a-second (IFAB, the governing body for the Laws of the game, insists on goals being signalled immediately e.g. within five seconds).
Use in computer games
The use of the Hawk-Eye brand and simulation has been licensed to Codemasters for use in the video game Brian Lara International Cricket 2005 to make the game appear more like television coverage, and subsequently in Brian Lara International Cricket 2007. A similar version of the system has since been incorporated into the Xbox 360 version of Smash Court Tennis 3, although it is not present in the PSP version of the game.
- VIDEO PROCESSOR SYSTEMS FOR BALL TRACKING IN BALL GAMES esp@cenet Patent document, 2001-06-14
- Nine admits Hawk-Eye not foolproof » The Roar - Your Sports Opinion
- About ICC - Rules and Regulations
- Tennis: Nadal blames line calling system for losing - 02 Mar 2007 - nzherald: Sports news - New Zealand and International Sport news and results
- Gulfnews: Hawk Eye leaves Nadal and Federer at wits' end
- "Hawk-Eye challenge rules unified". 2008-03-19. Retrieved 2008-08-22.
- BBC - Press Office - BBC Sport to feature Hawk-eye in World Snooker Championship coverage
- Cricinfo - Hawk-Eye bought by Wisden Group
- Uses in football (soccer): TimesOnline website.