Hawk-Eye Tennis Officiating System

By Deane Barker on September 8, 2006

Love all…for instant replay at U.S. Open: The animated instant replay system has been a hit at the U.S. Open so far.

If the player chooses to consult the replay (each player is allowed two challenges per set), an animated image of the ball hitting the court zooms into focus on giant screens around the stadium.

The effect is so entertaining that tennis officials have actually asked the Hawk-Eye technicians to delay showing instant replays for a few extra seconds to allow suspense and excitement to build.

Alas, tennis has been sullied by technology. Here’s a more detailed narrative. of how it actually works within a game.

And, of course, there’s a Wikipedia page.

Hawk-Eye uses six or more television cameras situated around the ground, linked to a computer system. The computer reads in the video in real time, and tracks the path of the ball on each camera. These six separate views are then combined together to produce an accurate 3D representation of the path of the ball, which can be viewed in a virtual reality simulation.

Why don’t they just use a camera in slow motion?



  1. My guess to why slow motion isn’t good enough is that, even with slow mo the compression and path of the ball from a single viewpoint doesn’t show enough. The combined view and elongated path with the balls compression spread shows exactly where the ball did or did not touch. I’m on vacation and watched a few reviews, it is neat. But it doesn’t allow any McEnroe types to develop and make the game actually interesting… these guys hit the ball so fast it’s almost like watching ping pong, no fun!

  2. So how does Hawkeye account for the different spins that the ball is hit with. The reason I bring this up is because the different spins would cause a different compression of the ball upon impact. Since so many of these balls are so close to the line the system must be accurate to the milimeter. Which brings me to my next question. What is the variance for the system?

  3. The hawkeye is wrong. A tennis ball is a sphere, not a disc or hockey puck. When a replay shows the edge of the ball just over a line, the ball is out by just under the radius of the ball. The center of the ball is always the first part of the ball to touch the court. No matter how the ball is distorted by spin, the edge can never be the first part of the ball to contact the court regardless of what direction the ball is coming from. Please explain why no one seems to recognize this obvious fact.

  4. Sorry to tell you Jack Howard but as you said the ball is A SPHERE meaning the ball does not have an an edge anyway

  5. Jack howard totally agree with you. Hawkeye works by an overhead camera covering the whole court.

    So the overhead graphic of the ball does show an edge to the ball. If the graphic was a 3D from court level with the grass then the touching surface on the court would be seen.

    Commentators kept saying oh it clipped the line by millemeters, well no it did’nt because the graphic is overhead of the ball and that mm that is on the line would not be touching the line at all because the part of the ball touching would be outside the line.

    I cannot believe this is being used on Grand slam tournaments worth millions of pounds when it is a completely useless gadget.

    that is all

  6. The line judges are looking at a straight on “profile” view to see where the bottom of the ball touches the ground and line,

    And Hawk-eye looks at a “plan” view from up above which will look like it is touching the line but in fact is not.

  7. Have any of you ever held a tennis ball? You can squeeze them in your hand!! With the force that these players are actually hitting the ball, and the speed with which it contacts the ground, the profile of the ball in contact with the ground changes. The Hawk-eye system calculated this (amongst its many millions of calculations per rally) and projects this onto the graphical representation of the court.

    You should all note that this system is NOT a “video replay” but a computer constructed and calculated model from the data collected by multiple cameras around the court which track the ball in 4 dimensions in real time.

    Therefore, the trailing “edge” (formed by compression of the ball on impact with the court) can indeed spread to be in contact with the line by millimetres.

  8. What the virtual reality shows is the part of the ball that contacts the ground It would help to avoid confusion if they also simulated over this image the rest of the ball which of course is larger than the contact part. This would avoid the confusion some people posting seem to have.

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