Vision and Sport- incredibly interesting and a lot of additional reading and analysis provided here
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Course
Active Vision
Institution
Cardiff University (CF)
This lecture is very interesting especially for a football fan!
It explores why there is such a great difficulty in detecting whether a player is offside or not, due to an error in our vision (flag error or no flag error).
It explores motion extrapolation, apparent ball size, and why goalkeepers ...
The Referee:
The problem of making an offside judgement is very important in football.
Offside: striker cannot stand in between the opposing teams goal and defenders
whilst the ball is in play.
Oudejans et al (2000): argue that what matters is that when people make
judgements about offside, that they don’t make judgements of where people are
in the world, but where they are in relative position in the retinal image.
So there is an influence of position of assistant referee.
Ideas:
Flag error: if attacker is behind the defender so not between the goal and
defender, but the referee has to make a judgement as to whether the attacker is
offside. In the retinal image, it looks like the attacker is offside, because of the
position of the referee. They should be able to judeg the relative positions of the
people with respect to the pitch, but they are judging the relative positions based
on what they can see. So therefoer this could lead the AR to make an offside
judgement when they arent – this is a flag error (say they're offside when they're
not).
No Flag error: position of referee can also affect them from seeing when the
attacker actually is offside. So this is a no flag error.
Exp to test this:
Set up a camera on top of a building and film a few games
So they can work out when there is a real offside/not offside situation
Identified 200 potential offside situations
And 179 where the referre is beyond the defender (closer to the goal than the
defender)
Found that 40 errors were made.
Conclusions: allows them to make predictions about the number of flag errors
that will be made about the different locations of the players.
Players on the outside of the defender: when on the far side of the pitch from the
AR, there will be more FEs than NFEs, whereas on the near side to the AR,
players on the outside of the defender will get more NFEs than FEs.
When the attacker goes inside the defender: on the far side of the pitch more
NFEs than FE’s should occur, and more Fes than NFEs should occur on the near
side.
Errors made by ARs in judging offside may often be the result of the relative
optical projections of the players on the ARs retina. This means that, regardless
of the quality of the AR, judgement errors are inevitable owing to the apparent
limitations of our perceptual system. Suggest that should use a better technique
such as a video.
**Mallo et al (2012): found that top class international referees experienced a
14% error rate when judging foul play incidents whereas assistant referees
presented a 13% error rate.
found that more errors are made within the second half of a game than the first
half, particularly in the last 15 minutes of a game. They suggest that this may be
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