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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It’s obvious why Thais can’t resist our English footballers. But they want our schools, too

The only explanation is . . . our footer must be great and exciting to watch.

At Bangkok airport, sitting in the Club lounge, as I am a toff, I spotted a copy of Thailand Tatler, a publication I did not know existed. Flicking through, I came across a whole page advert announcing that RUGBY SCHOOL IS COMING TO THAILAND.

In September, Rugby will open a prep and pre-prep department, and then, in 2018, full boarding for ages up to 17. How exciting – yet another English public school sets up a satellite in Thailand.

But I was confused. Just as I was confused all week by the Thai passion for our football.

How has it happened that English public schools and English football have become so popular in Thailand? There is no colonial or historical connection between the UK and Thailand. English is not the Thais’ first language, unlike in other parts of the world such as India and Hong Kong. Usually that explains the continuation of British traditions, culture and games long after independence.

When I go to foreign parts, I always take a large wodge of Beatles and football postcards. I find deprived persons all over the world are jolly grateful for these modern versions of shiny beads – and it saves tipping the hotel staff. No young Thai locals were interested in my Beatles bits, but boy, my footer rubbish had them frothing.

I took a stash of seven-year-old postcards of Andy Carroll in his Newcastle strip, part of a set given away free in Barclays banks when they sponsored the Premier League. I assumed no one in Thailand would know who the hell Andy Carroll was, but blow me, every hotel waiter and taxi driver recognised him, knew about his various clubs and endless injuries. And they all seemed to watch every Premiership game live.

I have long been cynical about the boasts that our Prem League is the most watched, the most popular in the world, with 200 countries taking our TV coverage every week. I was once in Turkey and went into the hotel lounge to watch the live footer. It was chocka with Turks watching a local game, shouting and screaming. When it finished, the lounge emptied: yet the next game was our FA Cup live. So I watched it on my own. Ever since, I’ve suspected that while Sky might sell rights everywhere, it doesn’t mean many other folk are watching.

But in Thailand I could see their passion, though most of them have no experience of England. So the only explanation is . . . our footer must be great and exciting to watch. Hurrah for us.

Explaining the passion for English public schools is a bit harder. At present in Thailand, there are about 14 boarding schools based on the English public-school system.

Rugby is only the latest arrival. Harrow has had a sister school there since 1998. So do Shrewsbury, Bromsgrove and Dulwich College (recently renamed British International School, Phuket).

But then I met Anthony Lark, the general manager of the beautiful resort where I was staying in the north of the island. He’s Australian, been out there for thirty years, married to a Thai. All three of his sons went to the Phuket school when it was still Dulwich International College.

His explanations for the popularity of all these British-style schools included the fact that Thailand is the gateway to Asia, easy to get to from India and China; that it’s relatively safe; economically prosperous, with lots of rich people; and, of course, it’s stunningly beautiful, with lovely weather.

There are 200,000 British expats in Thailand but they are in the minority in most of these British-style public schools – only about 20 per cent of the intake. Most pupils are the children of Thais, or from the surrounding nations.

Many of the teachers, though, are from English-speaking nations. Anthony estimated there must be about five thousand of them, so the schools must provide a lot of work. And presumably a lot of income. And, of course, pride.

Well, I found my little chest swelling at the thought that two of our oldest national institutions should be so awfully popular, so awfully far away from home . . . 

Hunter Davies is a journalist, broadcaster and profilic author perhaps best known for writing about the Beatles. He is an ardent Tottenham fan and writes a regular column on football for the New Statesman.

This article first appeared in the 27 April 2017 issue of the New Statesman, Cool Britannia 20 Years On

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