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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Celebrate Labour's electoral success – but don't forget the working class

The shutting down of genuine, constructive debate on the left is the great danger we face. 

In the moment when the exit poll was released on 8 June, after seven weeks of slogging up and down the streets of Britain, dealing with scepticism, doubt and sometimes downright hostility, we felt a combination of relief, optimism, even euphoria.
 
This election broke wide open some assumptions that have constrained us on the left for too long; that the young won’t vote, that any one individual or political party is “unelectable”, that perceptions of both individuals, parties and even policies cannot change suddenly and dramatically. It reminded us that courage, ambition and hope are what’s needed and what have been missing from our politics, too often, for too long.
 
We have learnt to tread carefully and wear our values lightly. But in recent weeks we have remembered that our convictions can, as Jonathan Freedland once wrote, “bring hope flickering back to life” and meet the growing appetite for a politics that doesn’t simply rail against what is but aspires to build a world that is better.
 
In this election at least, it seems the final, anticipated fracture of Labour from its working-class base after Brexit did not materialise. Shortly before the snap election was called I wrote that while Brexit appeared to be Labour’s greatest weakness, it could just be our biggest strength, because: “consider what remain voting Tottenham and leave voting Wigan have in common: Labour… We will succeed if we seek the common ground shared by the decent, sensible majority, and more importantly, so will Britain.”
 
But consider this too. The Tories ran a terrible campaign. It was, without any doubt,the most inept, counter-productive campaign I’ve ever seen in British politics. The day their manifesto hit the headlines, even in our toughest neighbourhoods, we could feel change in the air. Arrogance is never rewarded by the British people and Theresa May has paid a price for it. Yet, despite a Tory manifesto that was a full, square attack on older people, the majority of over 65s still came out for the Tories.
 
And despite the growing relevance of freedom, internationalism and tolerance in an era characterised by Donald Trump and Vladimir Putin, the Liberal Democrats managed to become bystanders in the political debate. They stood on a platform that aimed to capture the support of those remain voters for whom Brexit is the major question, but neglected the rest. And they quite spectacularly failed to foresee that those who were intensely angered by May’s conversion to a little England, hard Brexit stance would vote tactically against the Tories. Over those seven weeks, they all but disappeared as a political force.
 
As Bob Dylan once said, "the times, they are a-changin" – and they will change again. The recent past has moved at extraordinary speed. The Brexit Referendum, the rise and retreat of nationalism, the election of Trump and his crushing unpopularity just a few months later, the reversal in fortunes for May and Jeremy Corbyn, the astonishing phenomenon of Emmanuel Macron and pro-European centrism, and the dramatic rise and sudden collapse of Ukip. Politics, as John Harris wrote last week, is now more fluid than ever. So now is the time, for hope yes, and for conviction too, but not for jubilation. We need some serious thinking. 
 
We should be cautious to rush to judgment. It is only two weeks since the exit poll sent shockwaves across the country. There is no comprehensive explanation for the multitude of motivations that delivered this election result and will not be for some time. But there are some early indictors that must make us think. 
 
After seven years of austerity, as John Curtice observes, the Tories made some of their biggest gains in some of the poorest areas of Britain. It is something I felt in all of the eight constituencies I campaigned in during the election. While the Labour vote rose significantly in towns like Wigan, so too did the Tory vote, despite little or no campaigning activity on the ground. As Rob Ford puts it, “Labour, founded as the party of the working class, and focused on redistributing resources from the rich to the poor, gained the most ground in 2017 in seats with the largest concentrations of middle-class professionals and the rich. The Conservatives, long the party of capital and the middle class, made their largest gains in the poorest seats of England and Wales… Britain’s class politics has been turned completely upside down in 2017”.
 
To acknowledge the growing, longstanding scepticism of many working-class men, and women, towards Labour in towns across England is not to take away from the hard work and drive of the activists, advisers and politicians that helped to fuel such a dramatic turnaround for Labour during the short campaign. To have won considerable gains in wealthier suburbs is no small achievement. 
 
But if the future of Labour lies in a coalition between middle-class young professionals and the working class, what is the glue that binds? While there is shared agreement about investment in public services, how are those interests to be squared on areas like national security and immigration? I believe it can and must be done, but – as I said to conference when I was first elected seven years ago - it will demand that we begin with the difficult questions, not the easy ones.  
 
Just a few days before the election, statistics were released that pointed to a collapse in trade union membership. What does the decline of an organised Labour movement mean for who we are and what we can achieve? These are not new questions. They were posed by Eric Hobsbawm in his brilliant lecture, "The Forward March of Labour Halted" in 1979 - a challenge laid down in the year I was born. Now, 37 years on, we are no further down the road to answering it. 
 
The most dramatic finding from this election was the support Corbyn’s Labour party appears to have won from middle-class, young professionals. They said he couldn’t do it and quite stunningly it seems they were wrong. But a ComRes poll last week caught my eye – by a large margin those 30-44 year olds would favour a new centre-ground political party over the current political settlement. In an election where we returned strongly to two-party politics, it appears they moved to us. But what would a dynamic and renewed Liberal Democrat Party, or a British En Marche do to our support base?
 
After a hellish two years we have learnt in Labour, I hope, that unity matters. The public and private anger directed towards each other, whether the Labour leadership, the parliamentary Labour party or elected councillors, is desperately damaging and its (relative) absence in the campaign was important.
 
But unity is not the same as uniformity, and while two weeks ago I felt there was a real danger of historic fracture, now I believe the shutting down of genuine, constructive debate on the left is the great danger we face, and must avoid. No one person, faction or party has ever had the monopoly on wisdom. The breadth of the Labour movement was and remains our greatest strength. 
 
Consider the Labour manifesto, which drew on every tradition across our movement and demanded that every part of the party had to compromise. Those broad traditions still matter and are still relevant because they hear and are attuned to different parts of Britain. Our country is changing and politics must catch up. The future will be negotiated, not imposed.
 
As we witness the age of "strong man" politics across the world, here in Britain our political culture has become angrier and more illiberal than at any time I can remember. The Brexit debate was characterised by rage, misinformation and a macho political culture that demanded that we abandon nuance and complexity, an understanding of one another and tolerance of different points of view.
 
But this is not where the future of Britain lies: it lies in pluralism. It lies in a politics that is nimbler, more fleet of foot, less constrained; a return to the great tradition of debate, evidence, experience and argument as a way to build broad coalitions and convince people; not shouting one another down, nor believing any of us are always right; an arena in which we listen as much as we speak; a political culture in which we are capable of forming alliances within and across party lines to achieve real, lasting change.
 
And ultimately that’s the prize: not just seek power but, to paraphrase a philosopher whose work inspired millions, in the end “the point is to change it”. We could sit tight in Labour and hope to see the current government fall apart. We might even inherit power, we could temporarily reverse some of the worst of the last seven years, but what then? If we have learnt anything from 13 years of Labour government it should be this: that to build lasting change is the hardest political task of all, and it requires now that we do not turn to the political culture, the tools or even the ideas of the past, but that we think hard about where the future of our movement and our country really lies. Now is not the time to sit back and celebrate. Now is the time to think.

Lisa Nandy is the MP for Wigan. She was formerly Shadow Secretary of State for Energy and Climate Change.

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