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# Tennis rules- in or out

Wed 4 Jul, 2012 01:33 pm
At Wimbledon the Hawkeye system judges a ball in, if its diameter, seen from above, touches the line. Is that the official ruling? All I can find in the rules I've seen is 'If the ball touches the line it is in.' Although the diameter from above touches, the actual contact may be outside the line surely? have the Hawkeye setters interpreted their own version of this rule?
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Type: Question • Score: 4 • Views: 4,359 • Replies: 8
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ossobuco

1
Wed 4 Jul, 2012 01:59 pm
I don't know the answer, but see why you ask it.

Maybe others here know..
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aspvenom

2
Wed 4 Jul, 2012 02:07 pm
http://www.topendsports.com/sport/tennis/hawkeye.htm
Quote:
Of the player challenges that have been made, subsequent rulings by Hawkeye have shown that they are only correct about 46% of the time.

Quote:
Anyone who has watched a match on TV where they have used this system may have noticed that the ball seems to be elongated when projected on the court surface. This may be explained by imagining the ball hitting the ground with a lot of topspin, that it actually spun forward on the ground and deformed so much as to flatten on the ground. The mark doesn't have to have the exact surface area of the cross-section of the ball to accurately represent the impact point of the ball.

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aspvenom

2
Wed 4 Jul, 2012 03:48 pm
Disclaimer: I don't know anything about tennis, sorry
Being a physics geek, and thinking this through, I can give you a few suggestions.

The Hawkeye-system will track the real world path of the ball, and then this data goes into the system in order to predict the path of the ball.

The first part tracking the real world path of the ball, and once the positions of image of the ball are registered in the detection process, the next step is triangulating the point of ball in a 3 dimensional coordinate system.
In a simple theoretical world we can ignore air drags, and spins (fluid mechanics), and the the ball will follow a parabolic path as per Newton's laws of motion and gravitation.

I don't know if the Hawkeye system used in tennis would use equations to take into account fluid mechanics, as I mentioned above such as, drag and spin.
If not, Hawkeye's predictive powers are somewhat limited, because It can predict where a ball will go, by extrapolating the existing trajectory of the ball. So it has the ability to make the measurement non-intrusively from long distances for high speed projectiles, therefore the accuracy of the prediction of the ball maybe some small percent off.

That said, due to speed of the projectile (tennis ball) which moves faster at times that our eyes can't judge its exact trajectory, the Hawkeye system is on average more accurate than our perception.

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rosborne979

1
Wed 4 Jul, 2012 08:16 pm
I don't know exactly how the Hawkeye system works, but it seems to be far more accurate than the human eye, and it's always consistent within its own parameters.

I suspect that the system is programmed to take into account the "squash" of the ball as it bounces, so even though a single point impacts the surface initially, a much larger surface area of the ball eventually mashes down onto the surface (probably almost the diameter of the ball). So the original calibration you suggested in your post may be logical.
Val Killmore

0
Wed 4 Jul, 2012 09:08 pm
@rosborne979,
Wikipedia wrote:
In 2008, an article in a peer-reviewed journal[29] consolidated many of these doubts. The authors acknowledged the value of the system, but noted that it was probably fallible to some extent, and that its failure to depict a margin of error gave a spurious depiction of events. The authors also argued that the probable limits to its accuracy were not acknowledged by players, officials, commentators or spectators. They hypothesised that Hawk-Eye may struggle with predicting the trajectory of a cricket ball after bouncing: the time between a ball bouncing and striking the batsman may be too short to generate the three frames (at least) needed to plot a curve accurately. However, the paper did not attempt to establish the accuracy of the system, and the only technical information presented was taken from an article on the Cricinfo website.

The article also argued that Hawk-Eye's depiction of line decisions in tennis ignored such factors as the distortion of the ball on bouncing and the less-than-complete precision with which the lines on the court are drawn. The makers of Hawk-Eye strongly attacked many of these claims, but the authors have not withdrawn them.
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engineer

2
Thu 5 Jul, 2012 05:14 am
@rosborne979,
rosborne979 wrote:

I don't know exactly how the Hawkeye system works, but it seems to be far more accurate than the human eye, and it's always consistent within its own parameters.

Any that is the key point - all players get the same results because it is internally consistent. We will never have again the blatantly biased line calling of the 2004 US Open. If the hawkeye system gets one of 10,000 calls wrong, it will still be the fairest system we can devise.
rosborne979

1
Thu 5 Jul, 2012 12:48 pm
@engineer,
engineer wrote:

Any that is the key point - all players get the same results because it is internally consistent.
And that was my main point. Consistency, not micro millimeters, is the primary value of the system.

Although, as an academic exercise it's interesting to see just how precise they can be. Could the algorithm be modified to include the "fuzziness" of the ball and a few stray fibers which might hit the line?
brenden99

-1
Fri 13 Jul, 2012 02:15 am
@rosborne979,
I think that rule is very simple if that is gona change then it would be difficult for judgement so they make rules easier for all and for players as well.
You know even a smaller edge is touched with the line then it is called in the court.
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