Hawk-Eye keeps watch at Wimbledon

By Sarah Holt
BBC Sport at Wimbledon

Hawk-Eye shows where Andy Roddick hit his serves

Just why is it that we do not get to hear BBC tennis expert John McEnroe bellow, "You cannot be serious," anymore?

And how come we now know for certain that Tim Henman has finally got to grips with his second serve?

The answer is Hawk-Eye - a sophisticated, virtual reality system that can tell whether a ball is in or out, as well as analyse a player's match strategy.

BBC Sport asked founder Paul Hawkins, who introduced his invention to the Wimbledon commentary team in 2002, to explain how it works.

EYE ON THE BALL

"There are five high-speed cameras high up in the roofs of Centre Court and Court One which accurately track the ball as it flies through the air," says Hawkins.

"A computer captures the image from each camera and works out where the ball is.

"By finding the ball in multiple cameras we can find out where the ball is in 3D space - where it is in the real world if you like.

"The computer then combines all this information and traces the trajectory of the ball in each rally.

"This information is then sent to the virtual reality machine which produces the graphic images that you see on the television.

"So Hawk-Eye is able to show where the ball landed in every point played."

TRIED AND TESTED

"The bounce mark of the ball that Hawk-Eye shows is accurate to 3mm," explains Hawkins.

"We also take into account the amount the ball compresses and skids on the court.

HAWK-EYE ON HENMAN What Hawk-Eye saw during Tim Henman's victory over Mark Philippoussis Henman's return of serve was excellent. He got the ball consistently low over the net to make it difficult for Philippoussis to hit that first volley Henman has become more aggressive on his second serve - his average second serve speed is up by 10mph on last year If Henman missed a second serve it was generally long which is a sign of over-confidence Henman's tactics were different from previous rounds but were spot on - his volleying was superb

"Hawk-eye aims to resolve controversial decisions so in tennis that is often line-calls.

"We also aim to give the viewer a greater understanding of the sport by putting Centre Court into the living room.

"The BBC commentators often give us the lead because we hear what they're talking about and then try and back it up with statistics.

"Hawk-Eye can really show the story of the match in a way that normal television cameras can't.

"Each match generates a database of various statistics and it is up to a member of the team who has a knowledge of tennis to work out what is relevant.

"We can analyse service patterns, for example, where the players are serving if they are using kick or slice.

"Hawk-Eye finds out if certain players target the opponent's backhand or forehand.

"We can also look at how the court is changing as the tournament progresses."

EYE ON THE FUTURE

"I think there is a strong body of opinion that Hawk-Eye should be used to help umpires make official decisions," says Hawkins.

"We did an event last November where the umpires used it if a player disputed a bad call but it was a non-ATP Tour event.

"After Wimbledon our plan is to set up a test and have the International Tennis Federation come down and evaluate it.

"Umpires already have Cyclops, so technology is already being used to help not replace them.

"You do have an obligation to make sure it's the players' ability that decides a match and not the mistakes of an umpire.

"But we do want Hawk-Eye to be used only if there is a dispute not by default.

"And often Hawk-Eye shows the umpire is correct so if anything we give the umpires credibility."