Crossing the line: How Hawk-Eye's goal line technology will work

Football stirs primeval passions in many supporters. Bad calls on the pitch unleash an onslaught of abuse towards the referee and his assistants, both at the ground and at home via the television. However, while goal line technology won't eliminate such discontent completely, fans in the future should at least have a lot more confidence about goal line decisions. This is because in July 2012, FIFA (international football's governing body) after many years of delay finally took the decision to adopt goal line technology across the world game. This decision came after an extensive study was undertaken to test the accuracy and reliability of various goal line technologies, the implications for stadium infrastructure and the associated costs. And, while FIFA has chosen to trial the German technology GoalControl for the Confederations Cup with a view to using it in the 2014 World Cup, the English Premier League has instead adopted UK-developed technology Hawk-Eye. After two years of trials and testing it was announced last month that Hawk-Eye has been awarded the contract to provide, implement and operate goal line technology across the 20 member clubs of the UK Premier Football League and all 380 matches in the 2013/2014 season starting in August. "The Premier League has been a long time advocate of goal line technology, and at times it didn't look like it would be something we would be able to introduce," says Premier League chief executive, Richard Scudamore. "However, since FIFA took the decision to permit it, we have been working hard to get a system in as soon as possible. Of the four companies that are currently licensed by FIFA, Hawk-Eye stood out for their excellent track record in delivering for sport over many years." Hawk-Eye was first used as a broadcast analysis tool for cricket matches in 2001. It visually displays the trajectory of the ball and then its most likely path as a moving image. This was originally used to determine whether an LBW decision had been correctly given, as well as to correlate the trajectory of all the balls in a given over or by a particular bowler. It was initially used as an insightful analysis tool by broadcasters and became an instant hit with punters, pundits and players alike. It has since become commonplace not just as a broadcasting tool, but as an officiating aid in tennis, snooker, Gaelic Football with future possibilities including baseball. Its success saw Hawk-Eye Innovations bought by Sony in 2011. Steve Carter, managing director of Hawk-Eye Innovations, says: "Hawk- Eye has many years' experience of successfully deploying its innovative technology for high-profile sports globally and can be trusted to provide a reliable long-term service to the game of football." The system uses seven high frame rate cameras and an advanced vision processing technique to instantly, accurately and reliably determine the location of the football. The cameras are usually located on the roof of a stadium, but there is flexibility around where the cameras can be installed without compromising accuracy. By relying totally on cameras and no modification to the ball or goalposts, it is totally non-invasive so will have absolutely no impact on any aspect of the game. Seven cameras installed at each goal end track the ball to within just a few millimetres. The images from each camera are processed instantaneously with each frame locating the ball. Extensive trials have shown the system to be so good at locating the ball, that even if only a small part is showing, it can still be tracked. The system is unaffected by mud on the ball or adverse weather conditions and the accuracy of the system is also not affected by any variances in the painting of the goal line or if the posts are not perfectly vertical. The system developed by Hawk-Eye can be set up to work with any pattern football and specific vision processing techniques have been developed to distinguish between different patterns on the football and manufacturers. "Football is fundamentally a simple game; whichever side scores the most goals wins," adds Scudamore. "So, when one is scored, or indeed not scored, and we have the ability through technology to definitively know whether the ball crossed the line, we should absolutely use it." In addition, the system uses a high-speed camera that is capable of removing players from the image, to allow the ball to become fully visible on replays. This feature gives broadcaster's immediate tracking graphics to show just where the ball was for close calls. It also gives broadcasters a new set of tools when it comes to analysis to show the trajectory of free kicks and the 'scatter' of shots on goal. "The fact it was a camera-based system was critical," says Scudamore. "Replays will be made available to all our host broadcasters and we are examining the feasibility of them being used on the in-stadia big screens. It's essential that fans see the system in action to know that it is working." As soon as the system detects that the ball has crossed the line it sends an instant message to a watch worn by the referee to indicate a goal has been scored. This happens within a second. If the ball didn't cross the line the watch will send the referee a 'near-miss' message for clarification that the ball did not cross the line, allowing him to signal play on or make another appropriate call. Hawk-Eye says that, 'there has never been a goal line incident where the ball would not have been seen by its cameras' and the accuracy is so good that no broadcast replays could, or would, disprove a decision. In other words, the replays offered by the system promise unequivocal proof the decision made is correct every time. Paul Hawkins, inventor of Hawk-Eye, says: "We understand the responsibility that we have been given, and that the real challenge lies ahead in consistently delivering the technology that football deserves." FIFA is keen to state that goal line technology is the only area where technology is going to be used. Offside decisions and other controversies are going to continue, probably until the Hawk-Eye technology proves useful and reliable beyond any doubt, and offers the potential to assist the referee in other aspects of the game. But England would have still won in 1966 regardless…wouldn't they?