Cricket, tennis and now football use Hawk-Eye - but how accurate is it?

Hawk-Eye's technology is an impressive tool that makes the lives of referees and umpires easier, but don't be fooled - there's a chance that Hawk-Eye could sometimes get a call wrong.

Hawk-Eye is a device used to reconstruct the track of the ball for LBW decisions in cricket and for line calls in tennis. It will be much in evidence during the remaining Ashes tests and is now being used for goal-line decisions in Premier League football. The technology is at its best when officials make a really bad decision.

But there are things you might not know about Hawk-Eye. For instance, it cannot track the ball to a millimetre even though one might get this impression when watching some replays; in tennis, those shots shown to be touching the line by a hair’s breadth and called in might actually be out and vice-versa.

Few people realised that there was an issue with accuracy until my colleagues and I wrote about it in 2008; even top scientists were quite surprised until they thought about it.

How it works
Reconstructed track-devices such as Hawk-Eye work by using a number of TV cameras to record the position of the ball in each frame, then a computer reconstructs the path and projects it forward from the last frame.

These devices were first used to aid leg-before-wicket decisions in cricket. The projection-forward principle is the same in tennis since it is unlikely that a camera shutter will be open at the exact moment the ball hits the ground next to the line so the crucial position has to be estimated from a series of previous positions.

What we uncovered
From the frame-rate of the cameras and the speed of the ball, a back-of-an envelope calculation gave the range of possible accuracy and it turned out to be less than the replays suggested. So we telephoned the firm to talk about it and we hit a wall. As sociologists of science we had spent decades chatting with scientists about this kind of thing but suddenly we were told this information was private and lawyers were on call. Before we could publish our first paper we had to ask Cardiff University to back us in case we were hauled into court.

Our results were based on the range of possibilities for frame-rate and such other technical matters we could glean from the internet but detailed data for these devices was and still is secret. The International Tennis Federation refuses to release the details of its tests and the International Cricket Council also keeps its results under wraps. I have tried and tried to get the information from them and the scientists they commissioned to do the testing but am always met with the claim that the information is commercially sensitive.

Margin of error
The problem with reconstructed track devices is that their output is based on estimates. The position of the ball in any one frame is a blob of pixels. The future path of the ball must be extrapolated from at least three frames if the ball is swerving but if it is moving fast and the bounce point is near to the crucial impact point there may not be three frames.

Even with three frames, projections have errors and if, as in tennis, the ball distorts on impact, the footprint on which the line call is based is, again, the result of an inexact calculation – and so on. Hawk-Eye itself used to claim an average error of 3.6 millimetres; more recently it claims this has been improved to average of 2.2mms. However, particularly in tennis, the reliance on this technology to provide a definitive call means that this margin of error isn’t reflected in the replays, leading most fans to assume it is 100 percent accurate.

Accuracy, of course, will depend on the speed and the angle of the ball and many other factors which is why these are average figures and, as with all averages, on occasion the error will be bigger – sometimes much bigger. To know what is going on one needs details of the tests and the distribution of errors that resulted.

Tech and circuses
Assuming that tennis and football lovers, unlike enthusiasts for, say, the professional wrestling circus, want to see fairness as well as an entertaining spectacle, they ought to know more about how the technology is trying to work out what happened to the ball.

When the ball is really close to the line we should see something like a spinning coin to indicate that the final judgement has a lot of chance in it. The crowd would still get its decision and fun but something closer to the truth would be on display.

More and more, computers are able to simulate what looks like reality and this is dangerous for the future of society. The public needs to learn to question technological claims such as those that have been made for anti-missile weapons systems. In certain sports some spectators think that technology is infallible when it is not.

Paul Hawkins, the founder of the Hawk-Eye company, recently said our arguments were “typical of people who spent a lot of time in universities rather than on the tennis circuit”. He’s right, and thank goodness for that.

Harry Collins does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.The Conversation

This article was originally published at The Conversation. Read the original article.

 

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Andy Murray reacting to a Hawk-Eye call at Wimbledon, 2013. (Photo: Getty)
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What happens when a president refuses to step down?

An approaching constitutional crisis has triggered deep political unrest in the Congo.

Franck Diongo reached his party’s headquarters shortly after 10am and stepped out of a Range Rover. Staff and hangers-on rose from plastic chairs to greet the president of the Mouvement Lumumbiste Progressiste (MLP), named after the first elected leader of the Democratic Republic of Congo.

Diongo, a compact and powerfully built man, was so tightly wound that his teeth ground as he talked. When agitated, he slammed his palms on the table and his speech became shrill. “We live under a dictatorial regime, so it used the security forces to kill us with live rounds to prevent our demonstration,” he said.

The MLP is part of a coalition of opposition parties known as the Rassemblement. Its aim is to ensure that the Congolese president, Joseph Kabila, who has been president since 2001, leaves office on 19 December, at the end of his second and supposedly final term.

Yet the elections that were meant to take place late last month have not been organised. The government has blamed logistical and financial difficulties, but Kabila’s opponents claim that the president has hamstrung the electoral commission in the hope that he can use his extended mandate to change the rules. “Mr Kabila doesn’t want to quit power,” said Diongo, expressing a widespread belief here.

On 19 September, the Rassemblement planned a march in Kinshasa, the capital, to protest the failure to deliver elections and to remind the president that his departure from office was imminent. But the demonstration never took place. At sunrise, clashes broke out between police and protesters in opposition strongholds. The military was deployed. By the time peace was restored 36 hours later, dozens had died. Kabila’s interior minister, claiming that the government had faced down an insurrection, acknowledged the deaths of 32 people but said that they were killed by criminals during looting.

Subsequent inquiries by the United Nations and Human Rights Watch (HRW) told a different story. They recorded more fatalities – at least 53 and 56, respectively – and said that the state had been responsible for most of the deaths. They claimed that the Congolese authorities had obstructed the investigators, and the true number of casualties was likely higher. According to HRW, security forces had seized and removed bodies “in an apparent effort to hide the evidence”.

The UN found that the lethal response was directed from a “central command centre. . . jointly managed” by officials from the police, army, presidential bodyguard and intelligence agency that “authorised the use of force, including firearms”.

The reports validated claims made by the Rassemblement that it was soldiers who had set fire to several opposition parties’ headquarters on 20 September. Six men were killed when the compound of the UDPS party was attacked.

On 1 November, their funerals took place where they fell. White coffins, each draped in a UDPS flag, were shielded from the midday sun by a gazebo, while mourners found shade inside the charred building. Pierrot Tshibangu lost his younger sibling, Evariste, in the attack. “When we arrived, we found my brother’s body covered in stab marks and bullet wounds,” he recalled.

Once the government had suppressed the demonstration, the attorney general compiled a list of influential figures in the Rassemblement – including Diongo – and forbade them from leaving the capital. Kinshasa’s governor then outlawed all political protest.

It was easy to understand why Diongo felt embattled, even paranoid. Midway through our conversation, his staff apprehended a man loitering in the courtyard. Several minutes of mayhem ensued before he was restrained and confined under suspicion of spying for the government.

Kabila is seldom seen in public and almost never addresses the nation. His long-term intentions are unclear, but the president’s chief diplomatic adviser maintains that his boss has no designs on altering the constitution or securing a third term. He insists that Kabila will happily step down once the country is ready for the polls.

Most refuse to believe such assurances. On 18 October, Kabila’s ruling alliance struck a deal with a different, smaller opposition faction. It allows Kabila to stay in office until the next election, which has been postponed until April 2018. A rickety government of national unity is being put in place but discord is already rife.

Jean-Lucien Bussa of the CDER party helped to negotiate the deal and is now a front-runner for a ministerial portfolio. At a corner table in the national assembly’s restaurant, he told me that the Rassemblement was guilty of “a lack of realism”, and that its fears were misplaced because Kabila won’t be able to prolong his presidency any further.

“On 29 April 2018, the Congolese will go to the ballot box to vote for their next president,” he said. “There is no other alternative for democrats than to find a negotiated solution, and this accord has given us one.”

Diongo was scathing of the pact (he called it “a farce intended to deceive”) and he excommunicated its adherents from his faction. “They are Mr Kabila’s collaborators, who came to divide the opposition,” he told me. “What kind of oppositionist can give Mr Kabila the power to violate the constitution beyond 19 December?”

Diongo is convinced that the president has no intention of walking away from power in April 2018. “Kabila will never organise elections if he cannot change the constitution,” he warned.

Diongo’s anger peaked at the suggestion that it will be an uphill struggle to dislodge a head of state who has control of the security forces. “What you need to consider,” he said, “is that no army can defy a people determined to take control of their destiny . . . The Congolese people will have the last word!”

A recent poll suggested that the president would win less than 8 per cent of the vote if an election were held this year. One can only assume that Kabila is hoping that the population will have no say at all.

This article first appeared in the 01 December 2016 issue of the New Statesman, Age of outrage