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Comment by johndhi | Hacker News Reader

Hmm -- call me crazy, but I feel like the positioning of the camera might have wrongly decided the race for Lyles. The first torso to cross the line wins.

If you look at the still image in the article, Lyles' right shoulder is leaning forward and visible to the camera, positioned to his right.

But Thompson's left shoulder seem to be leaning forward, but is hidden in the camera by his head and neck. It's possible Thompson's left shoulder is ahead of Lyles' right shoulder, but the image doesn't seem sufficient evidence to conclude on that.

What do other think?

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According to this Reddit thread, the camera actually is the finish line:

> According to UCI regulations, the camera is the finish line.

> The painted line on the road or track is placed there as a visual reference for riders and spectators, and obviously organizers try to align the painted line with the photo finish camera as best as possible. But that's all it is - a visual reference. The finish line is officially defined as the plane of the photo finish camera, not the painted finish line.

https://www.reddit.com/r/bicycling/comments/1emivk1/dont_if_...

>> UCI regulations, the camera is the finish line

UCI is Union Cycliste Internationale, i.e. the biggest international governing body of cycling events. Not athletics (i.e. track and field). I checked out the C1.1 & C2.1 rulebook from the IAAF and I'm not seeing an equivalent rule. Just a lot of rules for how to place the camera and mark the lane lines and finish line in 19.13

index of all IAAF rulebooks https://worldathletics.org/about-iaaf/documents/book-of-rule...

direct PDF link to the English version of the 17 JAN 2024 C1.1 & C2.1 - Competition Rules & Technical Rules rules (2.5 MB PDF) https://worldathletics.org/download/download?filename=675a00...

Good find! While it doesn’t say it in so many words, this text seems to say a that the camera’s finish line is the official finish line (especially given the implied requirement that the finish camera be a line camera):

> Book C 19.22: Times from the Photo Finish System shall be regarded as official unless for any reason the appropriate official decides that they obviously must be inaccurate.

Woah! Helpful. I guess Thompson should learn to dive forward with his right shoulder next time!

commentators tangentially referenced this when they mentioned that lyles had "learned" how to make a good finishing lunge, but it was also heavily implied that they were talking about the timing of the lunge and not the mechanics.

Yeah, keep in mind at athletics competition, a "false start" is deemed to be anything within 100m of the actual firing gun - because that is deemed to be below the level of human perception, and therefore someone "bet" or "guessed".

So I can't imagine a human can take a conscious step to get a FIVE millisecond advantage over another.

Your comment just made me realize something. The 5 milliseconds which Lyles won by is shorter than the time it takes sound to travel between his lane and Thompson's. If the starting gun were on the outside of the track (it's not), then Thompson would have actually run the race faster, if measured from the time he perceived the sound.

In reality the gun is usually on the inside of the track, so it would be Lyles overcoming this (negligible) advantage.

There's a speaker behind each runner in the starting blocks to avoid that being a factor.

True, but each speaker is positioned slightly differently, because it's immediately behind the blocks but each athlete sets the blocks slightly differently (to accomodate their legs). So in theory...

Tbh, it's all just bullshit to me. Less than 20 years ago, this would have been an ex-aequo, and glorifying someone who happened to dive 5-milliseconds-better is just sad. The obsession with "having a winner", for the benefit of sponsors and image contracts, has taken sports in some ridiculous places.

That's somewhat the nature of sports: the actual results always have some amount of variance. The differences between athletes are often minute enough that with slightly different circumstances the result would have been different. Yet the pressure of a smaller number of contests with outsized prizes does make for dramatic highs when winning for the competitors as well as drama for the spectators.

Of course you can. A good drummer will not deviate from beat by that much.

This doesn’t really answer the question. The camera can only see the non-occluded portions of the plane. Since Thompson’s left shoulder is not visible in the image, we know that his shoulder crossed the image plane at a time at which it was occluded by his head. But without extrapolation, it’s not clear to me that we know when his shoulder crossed the line.

Good point. I guess if you're occluded to the camera, I was assuming the presumption is you haven't crossed the line. But it could still be arguable that he did cross the camera's finish line, it was just occluded.

It doesn't matter when Thompson's shoulder crossed the finish line, since the shoulder is not part of the torso.

The torso was chosen as the body part for determining when a runner crosses the finish line precisely because torsos were easy to identify/distinguish and there is no ambiguity as to a runner's torso.

you don't think shoulder is part of torso?

The exact location of the border line between the upper arm / shoulder and the “torso” would vary depending on the development of the upper body of an individual athlete and would not therefore be totally consistent. Based on anatomy, we can say that the endpoint of the torso is the outer end / articulation of the collarbone (clavicle).

Although the pelvic area is anatomically part of the torso, for consistency in photo finish judging, it is more practical to define the lower end of the torso as the horizontal cross section of the body through the hip line . . .

IAAF Photo Finish Guidelines (June 2015): https://worldathletics.org/download/download?filename=4423f7...

In Olympic track and field at least two cameras, mounted on opposite sides of the finish line, are required to be used. So the judges had available for their use both perspectives.

My knee-jerk internet reaction was "YOU ARE CRAZY" but then I took a breath and looked at the photo and I can see your argument. There is no point in a runner learning with their left shoulder forward since it will be difficult to place the exact spot behind their heads.

Thanks! Usually nutty conspiracy theorists online don't preface their statements with "call me crazy" but I was worried about that, ha.

I think it might be more fair if the camera was above the participants.

That sounds fine for the Olympics but rather awkward for a lower profile race at which someone just wants to roll a camera out to the track.

The same problem could also be addressed by having two cameras, one on each side of the track, synchronized and recording the same plane.

One could align the cameras into the same plane by putting a vertical array of distinctive marks (e.g. rapidly blinking LEDs) on each camera, above and below the optics and in line with it, such that each camera would see the other’s marks when correctly aligned.

> a vertical array of distinctive marks (e.g. rapidly blinking LEDs)

This doesn't work, as light beams diverge. Even taking a high-quality laser beam with a divergence of 0.1 milliradian (for comparison, a typical laser pointer is about 1-2 mrad), after crossing the 11 meters width of a 9-lane athletics track, you end up with a beam diameter of 2.2 millimeters. At the 10 m/s speed of the athletes and a 40000 fps framerate, they travel 250 micrometers between each frame.

I'm not sure what the issue you're describing is. If I have two devices, each with a camera and a line of marks, if they can each see each other's marks, then they are aligned to within the horizontal spread of the camera pixels. There are no lasers involved -- the marks can be paint, stickers, blinking wide-angle LEDs, etc. -- my suggestion to use blinking LEDs is just so that's it's more obvious when one is in the field of view of the camera.

You don't just need the cameras to see each other, you need them to be perfectly parallel to each other as well, as otherwise they're photographing along a different plane, which may give conflicting results.

Suppose camera A has line L_A on the camera. A’s optics and marks are both on L_A, so A’s image plane contains L_A and camera B’s image plane also contains L_A (you know the latter because you’ve aligned the cameras so camera B sees L_A). And vice versa: camera A sees L_B. In 3D Euclidean space, two distinct lines define a plane, and both camera’s are photographing planes that contain L_A and L_B, so both cameras are photographing the same plane.

More concretely, if the cameras are photographing along different but parallel planes, then they won’t see each other.

Your solution works in a geometric world, where light propagates in a perfect straight line of infinitesimally small width. That's not true in reality, where light propagates in an ever-expanding cone.

More concretely, you can have two cameras photographing along different but parallel planes that do see each other.

I'm pretty sure the arbiters at the most important race at the most important sport event know what they are doing :)

Not to mention there was no controversy afterwards.

it's a line scan camera so there is no angle. that picture is a composite.

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