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 to look out for in the 2016 local and devolved elections

Your guide throughout Thursday night and into Friday. 

22:00: Close of polls. My advice is to use this time to stock up on vital supplies, like energy drinks, dips and fast food. And also to open the New Statesman’s all-singing all-dancing liveblog, which I will kick off from 10pm.

23:00: First to declare will be borough councils in Sunderland and Tunbridge Wells.  Sunderland is a Labour stronghold while Tunbridge is a Conservative fortress and both elect in “thirds” – electing a third of their councillors every year, a break every four years, as councillors are elected once every four years.

So even if the Conservatives win all 25 seats in Sunderland or Labour storm Tunbridge, it won’t matter in terms of who runs services there. You may ask “Hey, isn’t this a really stupid way of running elections, designed to produce gridlock and political failure?” The answer to this question is “Yes!”

Though frankly if we see Labour gains in Tunbridge – they have three councillors there in total – David Cameron is going to have to start updating his LinkedIn pretty damn quick, but keep an eye out for how Ukip do in Sunderland.

23:30: Look out for Rugby, which also elects in thirds. The Conservatives took back control of this council in 2007 after years of it being hung. On a good night for Labour, they could knock it back into no overall control, and it’s places like this they need to be posting good results in if they want to get back into power in 2020. (Winning Rugby on a uniform swing would mean Labour was in power with a majority of eight.)

Less interesting is Tameside, another Labour stronghold, though watch out not only for how Ukip do but whether the Conservatives can come through the middle in any of the seats here. Overall, though, the non-Labour parties haven’t gone above double figures here since the 2010 election, so anything other than hegemony is a troubling sign for Labour.

00:00: Remember Nuneaton, commonly known as the site of Ed Miliband’s Waterloo? (It was defeat here in 2015 that made it clear that not only were Labour not on course for victory, but that defeat was going to be worse than many predicted.) Well, half of the council seats there are up for grabs in the council of Nuneaton and Bedworth. Nuneaton and Bedworth elect in halves – where, spoiler alert, they elect half their councillors every two years. Although Nuneaton has a Conservative MP it is solidly Labour at a local level and anything other than a Labour hold here would be very worrying.

Keep an eye out for the Labour strongholds of Wolverhampton and Sefton, both of which elect in thirds. There really should be nothing to see there, but if things are going badly, you might see Ukip making some gains.

Southend-on-Sea is a lot of fun – this true-blue seaside town is run by a Labour coalition with a group of independent parties, after a long period of rule by the Conservatives. Can Labour and its ragtag coalition keep control? Demographic change is very slowly moving Southend towards Labour, so keep an eye out for some progress here.

00:30: Another Labour council in Newcastle-Upon-Tyne, which likewise elects in thirds. The Liberal Democrats – remember them? – ran Newcastle from 2004 to 2011, so although a change of power is unlikely, if there is indeed a serious revival in Liberal Democrat fortunes since exiting the coalition, they should look to make some gains here.

01:00: Results will start to come through from the Welsh Assembly, with the rock-solid seat of Merthyr Tydfil and Rhymney. If Labour can’t win here, they can’t win anywhere, but watch out for how well Ukip can do here. Ukip’s rise in Wales is the “biggest polling movement you’ve never heard of”, in the words of Cardiff University’ Roger Scully, and if they get a strong second expect that to signal big, big gains in the List system. (Wales uses the additional member system, a combination of first past the past and an area list, similar to the list method for the European Parliament.)

In England, results will come in from Ipswich and the Wirral, which both elect in thirds. Ipswich is Labour-run with two Conservative MPs, while Wirral is Labour-run with two Labour MPs. The seats of Ipswich, Wirral West and Wirral South are all key marginals – so both parties will be hoping for good performances here.

01:30: Provided that nothing unexpected has happened, there should be two routine Labour victories in the safe seats of Sheffield Brightside & Hillsborough and Ogmore, by-elections which are being held on the same day. I wouldn’t rule out a good second for Ukip in Ogmore but other than that, nothing that interesting to see here.  

More interesting will be the councils of Bury and Swindon, both marginals. Bury is currently Labour-controlled while Swindon has been Conservative-run since 2003. Labour should win both if they are on a winning trajectory, although the fact it is on the thirds model means that a winning performance on the night might not be enough to take control in Swindon.

02:00: Is that a unicorn? No, it’s a Liberal Democrat run council! Eastleigh is one of just nine left in the country. The council elects in thirds and having been a one-party state in 2010, the effects of coalition mean that Eastleigh now sends a Tory to Westminster and has six Conservative councillors out of 44. Knocking out the two Tories who are up will have Tim Farron pouring champagne over himself, while the Conservatives will hope that they can continue their revival.

Scotpocalypse! The first results should come in from Scotland, with Cunninghame South, East Kilbride, Hamilton, Larkhall and Stonehouse, Na h-Eileanan an Iar, Rutherglen, Uddington and Bellshil all due to declare. With the exception of Rutherglen and Uddington and Bellshil, the SNP won all of those seats in 2011, but expect those two Labour seats to turn a pleasant shade of yellow.

There should be better news for Labour in Blaenau Gwent in Wales, which is also due to declare.

02:30: Councils, councils, everywhere. Basildon, Birmingham, Coventry , Lincoln, Stockport, Walsall are the ones to watch. We’ll have an idea who is having a good night after they declare.

The yellowcoats are coming, the yellowcoats are coming! Watch out for the result from the constituencies of Orkney and Shetland, both solidly Liberal Democrat. If the SNP take both, expect a clean sweep of every constituency in Holyrood, with the other parties exiled to the lists. Less exciting will be Perthshire South & Kinross-shire, Perthshire North, and Stirling , all of which ought to go SNP.

And more news from Wales: Alyn & Deeside, Carmarthen East & Dinefwr, Delyn, Yyns Mon and Vale of Clywd all declare. The Vale is one of a handful of seats that Labour won in the 2011 Assembly elections but lost in 2015 to the Conservatives – Labour has to hold onto and ideally do better in those seats this time – look out for Gower, Cardiff North and the Vale of Glamorgan later on in the night, too.

03:00: It all kicks off around here. (If you wanted, you could probably get away with going to bed at 8 and setting your alarm for three.)

Crunch time in Wales, with Aberavon, Aberconwy, Arfon, Brecon & Radnorshire, Clywd South, Clwyd West, Dwyfor Meirionnydd, Gower, Montgomeryshire, Neath, Swansea East, Swansea West, Wrexham, Caerphilly, Islwyn, Newport East, Newport West, Ceredigion and Monmouth all due to the declare. By 4am we should have a clear idea of who’ll be running Wales. (Spoiler alert: it will be Labour, with the question being whether they will be able to govern alone or will have to make a deal with Plaid Cymru and/or the Liberal Democrats.)

Ones to watch: Aberconwy, a three-way marginal between Labour, the Conservatives and Plaid, currently Tory-held. And Gower.

Meanwhile, in England, Bolton, Crawley, Dudley, Exeter, Great Yarmouth, Harlow, Hastings, Plymouth, Southampton, Stevenage and Thurrock are the councils to watch as a whole bunch come in. Bolton, Southampton and Plymouth are Labour-run and home to seats that were Labour in 2010 but went to the Tories in 2015 – Labour should hold on comfortably if they are to have  shot at winning back those constituencies in 2020. Harlow, Hastings, Crawley and Stevenage are Labour-run but Conservative since 2010 at the latest, and are places where Labour should consolidate power.

Can Tim Farron win on his own doorstep? A third of seats in South Lakeland, which includes his own seat of Westmoreland and Lunedale, are up for grabs. Even amidst general Liberal Democrat woe in 2015, his party actually gained two seats in Farron’s own seat and lost just two across South Lakeland. Expect a good night here.

And in Scotland, Angus North & Mearns, Angus South, Ayr, Carrick, Cumnock & Doon Valley, Clydebank & Milgavie, Cunninghame North, Dumbarton, Dumfriesshire, Dunddee City  East, Dundee City West, Galloway & Dumfries West, Greenock & Inverclyde, Kilmarnock & Irvine Valley, Strathkelvin & Bearsden will all declare.

03:30: Declarations from Edinburgh and Glasgow. It was Edinburgh that gave Labour its one MP in Scotland in 2015, but Edinburgh Southern, which holds the bulk of the wards in Ian Murray’s Edinburgh South seat, is already an SNP seat, while Edinburgh Central, which holds the remainder, is also already a fetching shade of yellow. But Edinburgh is still, despite having a near clean-sweep for the SNP at Westminster, one of the swingiest, most marginal-heavy cities in the United Kingdom, so something exciting could happen. (The word “could” is working very hard here.) Expect the SNP to win every seat in Glasgow, unless something untoward is happening.

In England, Redditch and Trafford are worth watching. Redditch was Labour until 2010 and Labour runs the council there – but they were defeated there in 2015 so it’s a must-win seat if Labour is to stay in the game for 2020. Trafford is an island of blue in a seat of red – it includes the safe Labour seats of Kate Green and Mike Kane, but also Graham Brady’s Tory stronghold – where victory would put Labour in a strong position at this stage of the parliament.

04:00: It never rains but it pours. Results to look out for are Cambridge, Carlisle, Colchester, Derby, Peterborough, Portsmouth and Slough. In Cambridge, if there is a Liberal Democrat revival, it will be here. Everywhere else is a straight Labour-Conservative battle.

And it’s decision time in Scotland, as Aberdeen Central, Aberdeen Donside, Aberdeen South & Kincardine North, Argyll & Bute, Clackmannanshire & Dunblane, Cowdenbeath, Dunfermline, East Lothian, Fife Mid & Glenrothes, Kirkcaldy and Moray all declare. But the newsworthy results will be in the list results from Glasgow and South Scotland, which should be announced. We’ll begin to know what the SNP’s opposition will look like at this point.

04:30: If you’re wondering “when’s best for a power nap?”, here’s not a bad shout. We should have a good idea of who’s had a good night, whether Labour is on an upward trajectory, if Cameron is in real difficulties, and who’ll be calling the shots in Cardiff and Holyrood by now. You can safely shut your eyes until 8am.

But if you’re as cool as me, you’ll stay up for a swathe of Scottish seats and at...

05:00: Results from the Scottish list system will start to come through.

In England, if the Greens are going to make any sort of splash tonight it’ll be in places like Norwich, where they are already the official opposition to Labour. The signs from by-elections so far is that Corbyn’s Labour goes down a treat in cities like Norwich, so there is a real risk that Labour could do them serious damage here. Getting out with the same number of seats, or even more, would indicate that there is life for the Greens even while Corbyn is Labour’s centre-forward.

Also keep an eye on Reading, one of a number of councils that is Labour at a local level but Conservative at Westminster. Labour really mustn’t fall back in places like if they are to have a shot at power in 2020. We’ll get the last results from Wales, with Cardiff North and the Vale of Glamorgan two to watch out for.

05:30: Results from the Lothian region will come in from Scotland. It’s these party list votes that will be responsible for the bulk, probably the entirety, of the non-SNP presence at Holyrood. 

07:00: We should have results from the list vote in Wales, where Ukip will likely do well, while the last few regions from Scotland should report in too. Votes start being counted in the mayoral races. You can grab a cheeky two and a half hour sleep about now.

09:30:  Results from the mayoral contests in Liverpool, Bristol, London, and Salford will come in. Expect fairly quick declarations from Liverpool, Salford and London, all of which look fairly likely to return Labour candidates by large majorities. Bristol is a trickier test for Labour though it is another part of the country where Labour ought to gain a boost from having Corbyn as leader.  It could be as late as 17:00 if the contests are close.

11:00: The excitement begins anew, as Cannock Chase – Labour at a local level, Conservative at Westminster declares.

11:30: Kirklees, which contains the marginal seats of Wakefield, Colne Valley, and Dewsbury, declares.

12:00: Another rare Liberal Democrat local authority in the shape of Cheltenham. They elect in halves and the council was last up in 2014. The Liberal Democrats held the constituency of Cheltenham from 1992 until 2015, when the Conservatives regained a seat they had held without interruption since 1950. If the Liberal Democrats have a future, it’s in securing a big result here and using that to kick on and retake the seat in 2020.

Hyndburn (Labour nationally and locally) and Milton Keynes (Labour minority administration locally, Conservative in both Westminster seats) are the marginals to look out for. A great result for David Cameron would see them chip away at Labour’s majority in Hyndburn and take back Milton Keynes. A good result for Jeremy Corbyn would be a majority in Milton Keynes and advances in Hyndburn. Both elect in thirds.

12:30: Calderdale declares. Calderdale is made up of two marginals – Halifax, held by Labour’s Hollie Lynch, and Calder Valley, held by the Conservative Craig Whittaker. It’s currently run by a Labour minority administration. A good result for the Conservatives would be to tip the balance of power their way, a good result for Labour would be full control. The status quo would indicate that the 2020 election will look pretty much the same as the 2015 one.

13:00: Gloucester declares. Gloucester sent a Labour MP to Westminster until 2010 but is Conservative at a local and national level. Though the thirds model makes it difficult for Labour to take full control, knocking it into no overall control would indicate that Corbyn is on his way to becoming Prime Minister in 2020. Also declaring is Stroud, Conservative in Westminster but Labour locally. Defeat here would indicate Corbyn is on his way to Milibandtown in 2020.

13:30: Blackburn with Darwen. This is a weird unitary authority, combining solid Labour territory in Blackburn (though watch out for how Ukip do!) with more marginal areas in Darwen. And it elects in thirds. So, basically, if Labour do very well here, we’ll be able to tell. Otherwise, ¯\_(ツ)_/¯.

14:00: Pendle, currently no overall control but run by the Conservatives in coalition with the Liberal Democrats – hey sounds familiar! – has had a Tory MP since 2010. A good night here – Pendle uses the thirds model – would be good news for Labour’s chances in 2020.

15:00: Another unicorn aka Liberal Democrat-run Three Rivers, which has stayed orange despite no record of success at a Westminster level for that party since 1906. It’s up in thirds, so the Liberal Democrats are aiming for consolidation while the Tories are hoping for erosion.

Rossendale, which has sent a Conservative to Westminster since 2010 but is Labour run, has a third of its council seats up for election. An increased Labour presence on the council would indicate Labour was on course to take back the seat – a reduced one would suggest quite the reverse.

16:00: Get ready for the end of an era? Watford has been Liberal Democrat run since 2004 but their majority was slashed to just one in 2015. Get ready for a changing of the guard.

17:00: Rotherham elects in thirds and Ukip did spectacularly well last time on the back of a child sexual abuse scandal. Look out for their performance this time.

18:00: One last Labour-Conservative marginal fight in Warrington. A few late bloomers will declare over the weekend, but at this point you can go outside, get dinner or go to the pub.

Stephen Bush is special correspondent at the New Statesman. He usually writes about politics.