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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The Women's March against Trump matters – but only if we keep fighting

We won’t win the battle for progressive ideas if we don’t battle in the first place.

Arron Banks, UKIP-funder, Brexit cheerleader and Gibraltar-based insurance salesman, took time out from Trump's inauguration to tweet me about my role in tomorrow's Women’s March Conservative values are in the ascendancy worldwide. Thankfully your values are finished. . . good”.

Just what about the idea of women and men marching for human rights causes such ill will? The sense it is somehow cheeky to say we will champion equality whoever is in office in America or around the world. After all, if progressives like me have lost the battle of ideas, what difference does it make whether we are marching, holding meetings or just moaning on the internet?

The only anti-democratic perspective is to argue that when someone has lost the argument they have to stop making one. When political parties lose elections they reflect, they listen, they learn but if they stand for something, they don’t disband. The same is true, now, for the broader context. We should not dismiss the necessity to learn, to listen, to reflect on the rise of Trump – or indeed reflect on the rise of the right in the UK  but reject the idea that we have to take a vow of silence if we want to win power again.

To march is not to ignore the challenges progressives face. It is to start to ask what are we prepared to do about it.

Historically, conservatives have had no such qualms about regrouping and remaining steadfast in the confidence they have something worth saying. In contrast, the left has always been good at absolving itself of the need to renew.

We spend our time seeking the perfect candidates, the perfect policy, the perfect campaign, as a precondition for action. It justifies doing nothing except sitting on the sidelines bemoaning the state of society.

We also seem to think that changing the world should be easier than reality suggests. The backlash we are now seeing against progressive policies was inevitable once we appeared to take these gains for granted and became arrogant and exclusive about the inevitability of our worldview. Our values demand the rebalancing of power, whether economic, social or cultural, and that means challenging those who currently have it. We may believe that a more equal world is one in which more will thrive, but that doesn’t mean those with entrenched privilege will give up their favoured status without a fight or that the public should express perpetual gratitude for our efforts via the ballot box either.  

Amongst the conferences, tweets and general rumblings there seem three schools of thought about what to do next. The first is Marxist  as in Groucho revisionism: to rise again we must water down our principles to accommodate where we believe the centre ground of politics to now be. Tone down our ideals in the hope that by such acquiescence we can eventually win back public support for our brand – if not our purpose. The very essence of a hollow victory.

The second is to stick to our guns and stick our heads in the sand, believing that eventually, when World War Three breaks out, the public will come grovelling back to us. To luxuriate in an unwillingness to see we are losing not just elected offices but the fight for our shared future.

But what if there really was a third way? It's not going to be easy, and it requires more than a hashtag or funny t-shirt. It’s about picking ourselves up, dusting ourselves down and starting to renew our call to arms in a way that makes sense for the modern world.

For the avoidance of doubt, if we march tomorrow and then go home satisfied we have made our point then we may as well not have marched at all. But if we march and continue to organise out of the networks we make, well, then that’s worth a Saturday in the cold. After all, we won’t win the battle of ideas, if we don’t battle.

We do have to change the way we work. We do have to have the courage not to live in our echo chambers alone. To go with respect and humility to debate and discuss the future of our communities and of our country.

And we have to come together to show there is a willingness not to ask a few brave souls to do that on their own. Not just at election times, but every day and in every corner of Britain, no matter how difficult it may feel.

Saturday is one part of that process of finding others willing not just to walk a mile with a placard, but to put in the hard yards to win the argument again for progressive values and vision. Maybe no one will show up. Maybe not many will keep going. But whilst there are folk with faith in each other, and in that alternative future, they’ll find a friend in me ready to work with them and will them on  and then Mr Banks really should be worried.