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Who won the Amstel Gold Race? Human error in photo-finishes

504 points by tomglynch 5y ago

tomglynch 5y ago
OP here. I think the spoke movement is probably the most likely to be able to work out who reached the actual finish first. That is based on the spoke patterns in this image: http://tglyn.ch/blog/images/amstel_Finishphoto_AGR21.png http://tglyn.ch/blog/images/amstel_Finishphoto_AGR21.png The curve of the spokes should mean we can determine the distance the rider has traveled after the photo-finish camera. I cover my other ideas in the 'Further research required section' about 75% of the way down the article. If you have any further suggestions please let me know. Tom
- jhgb 5y ago
  > having it in the wrong spot means we may never know if Tom Pidcock's extra speed would have allowed him to make up the small distance in the final 26.86cm. Isn't it possible to extrapolate the movement from the last few frames of the image sequence?
  - tomglynch 5y ago
    Potentially - do you mean via the video or the photo-finish image? I've suggested in the article looking at when the wheel reaches 98% of the full height which I think is along the lines of what you're saying.
    - jhgb 5y ago
      I meant the photo-finish cameras, but nevermind, I forgot how these things worked. But I would expect high-speed 2D cameras being available today at the finish line as well.
- masswerk 5y ago
  I think, the spokes are a good approach, since these are actually objects recorded in time. However, I think @gorgoiler [1] has made a valid point regarding the intersection of the "finish plane" and the plane recorded by the camera. (On the photo shown on your blog, the camera appears to be mounted slightly behind the finish line, thus, intersecting the "finish plane" at the ideal height, should point to just before the finish line at ground level. But there isn’t sufficient information in the photo to measure such a minimal angle, or to confirm, if there's any at all.) [1] https://news.ycombinator.com/item?id=26977975 https://news.ycombinator.com/item?id=26977975
- eCa 5y ago
  Very nice write-up, it was a fun race to watch. On your future research, alternative 1: Instead of only looking at the width of the wheel, what about looking at the height/width ratio? The quicker wheel ought to be relatively more ”squished” horizontally. On the other hand, with the tight margins involved, it might be that the ratios are not comparable due to the fact that they are not the same distance from the camera.
- mnw21cam 5y ago
  The shape of the curves of the spokes doesn't depend on the speed. If you take the picture of the wheel, and fix the aspect ratio so that it is circular, then the spokes will have a curve independent of the speed of the wheel. Speed determination is purely based on the aspect ratio of the entire wheel. To reason on why this might be true - consider that the bottom of the wheel is stationary, and the top of the wheel is moving at twice the speed. This is the case regardless of the speed of the wheel. If you rolled the wheel past the camera really slowly, the entire wheel would be stretched out horizontally, but the spokes would all be in the same arrangement. The reason for this is that the camera is a fixed position line scan where the variable is time only. If we switch to thinking about standard video cameras with a rolling shutter, then these have a line scan where the variable is time and space - that is, the camera samples a scan that is moving at a known speed. If you have a video with a camera like this of helicopter blades, for instance, then you can determine the blade rotation speed from a single frame. But with this finish camera, that doesn't work. So, to determine speed, the best possible action is to pick two points on the rigid body that is moving, and time how long it takes to pass the recording line. The further apart these points are, the more accurate the average speed determination will be. The trade-off for this is that the speed measurement will be the average between the time the first point and the second point passes the recording line, and we are only interested in the average speed at the point the front of the bike passes the line. What we can show however, as pointed out elsewhere[0], is that one bike was in front of the other when the front of the wheel, the hub of the wheel, and the back of the wheel passed the recording point. When the back of the wheel passed the recording point, the front of the wheel definitely passed the actual finish line, so assuming the two wheels are the same size then the front of that wheel passed the finish line before the other one. [0] https://news.ycombinator.com/item?id=26978621 https://news.ycombinator.com/item?id=26978621
  - tomglynch 5y ago
    Great comment! Super informative and something I had not properly thought about. But you're totally right, curvature of the spokes is based only on the fact it's rolling past the camera, and two wheels rolling at different speeds will result in the same spoke pattern.
tgtweak 5y ago
Taking "Internet Detective" to new and exotic levels.
- tomglynch 5y ago
  Haha thank you - which part stood out to you?
  - disillusioned 5y ago
    Bro, literally all of it. What a great piece. Down to guesstimating the tire sizes, tracking down the line width, accounting for road camber, etc. Really enjoyed this.
    - tomglynch 5y ago
      Haha cheers! Enjoyed every moment of it (though I did spend quite a while on it all!)
deanpea 5y ago
Very interesting write up. Given the price of photo-finish cameras, I wonder if there’s a solution with slow motion cameras which could provide some margin for error as well as a better spectacle for viewers?
- tomglynch 5y ago
  Yeah true - it would be interesting if one of the super slow mo cameras they use in sports would be as good at determining the winner.
  - comex 5y ago
    Well, there are slow mo cameras that go well over the 2,000 or 3,500 FPS mentioned in the article. If oriented the same way, they would provide a strict superset of the information of a strip photography camera, since you could recover the strip photo by just extracting one column from successive frames of the video. It doesn’t seem like the price is even particularly different. I’m not an expert, though, just judging based on Google results. Maybe there is some obstacle I’m not thinking of.
- rocqua 5y ago
  Slow mo camera's produce too much data to run continuously. These camera's are used to determine the entire finishing order. They need to be running constantly.
  - ska 5y ago
    You could filter a lot of it out automatically - might be doable these days.
jrudolph 5y ago
Awesome research. I have similar quibbles about photo finish cameras in sports and written about them [0]. There are usually tons of rules in sport about the equipment, the Race course etc . but how exactly the finish needs to be set up is often vague. In this case it was an alignment issue at fault. But the next problem is the arbitrary resolution finish cameras work at. How wide is the pixel slot? This can be the difference between calling a tie or a small margin. [0] https://www.rowinginmotion.com/thoughts-fairness-rowing/ https://www.rowinginmotion.com/thoughts-fairness-rowing/
- tomglynch 5y ago
  Yeah the UCI rules for photo finish seem very vague, and also don't seem enforced. I haven't used a photo-finish camera myself but it seems to me the tech behind these is quite dated, the shots from the 1960s are almost as good except for the frame rate and number of pixels. Perhaps there is a better way.
xmprt 5y ago
This was a really good writeup. I thought for sure there would be no way to salvage it after you mentioned how they messed up but then you talked about using the curvature of the spokes and the width of the wheels in the photo finish to figure out how the wheels were spinning and it blew my mind.
abel_ 5y ago
I think the distortion of the video-finish camera should be considered when making these estimates. There's quite a lot of it happening in the shot. Narrowing down the specific camera intrinsic parameters may be a challenge. The EXIF data of the original footage might be fruitful. It might also be possible to undistort using some assumptions on colinear points in the video (i.e., the finish line and signs should have straight lines).
- tomglynch 5y ago
  Exif data is a good suggestion - I'll see what I've got EDIT: nah nothing interesting there. It may have been stripped when they emailed it to me?
- lostlogin 5y ago
  > It might also be possible to undistort. It might be possible to res it right up using that new photoshop feature. A joke obviously...
gorgoiler 5y ago
The “finish line” could be thought of as a two dimensional plane. The winner is the first person to touch or pass through the plane. If you’re painting a line then the “finish line” is where that plane touches the ground. For other races it might be a piece of tape held at chest height — the part of the body that usually goes through the plane first. When the competitors are bicycles then they all the same height — the middles of the front wheels are all the same height off the ground, something on the order of 400mm. The finish line is floating about a foot off the ground. The specialist streak camera photographs objects passing through a 2D plane. Ideally you would have that plane aligned vertically so that the finish plane and the camera plane were the same. If for some reason you couldn’t do that — let’s say the camera could only be placed a few feet in front of the finish line so as to see around an object — then you would have to arbitrarily angle the camera plane to intersect the finish plane. The intersection of these two planes will give you the “finish line”. For a bicycle race, do you set it up so that the finish line is on the ground, or floating 400mm above the ground? If you do the latter then the projection of the camera plane into the road will indeed give a line that stops short of the finish plane, but that’s irrelevant — the actual finish line at the middle of the front wheel is in the correct place. I think the article assumes the former when the organisers did the latter?
- tomglynch 5y ago
  Ah this is an interesting thought though I don't think this is what the organisers were trying to do. Or if they are, it does not match up with what they are meant to do as per the UCI specs (the UCI is the international cycling governing body). In another comment I was discussing the tech being somewhat outdated - perhaps your suggestion is part of the solution. Would two cameras on different planes result in more accurate results?
  - gorgoiler 5y ago
    It’s probably quite hard to make an orthographic streak camera that is pointing vertically down in the same plane as the finish, but that seems like the optimal solution. Moreover, if the camera is used to identify the times and finish positions of all the riders, it’s probably quite hard to identify them from above. Perhaps a streak video synchronised with TV footage would be convincing? How about a prismatic laser and fog machine at the finish? It’ll look like an 80s rave but the streak camera will clearly show where the finish is.
runningmike 5y ago
Great research! But van Aart is the right winner. The photo finish picture is stated s the official result. Every athlete knows that, despite alignment errors of the equipment.
- djmips 5y ago
  Exactly. It's a bit arbitrary but it's the final call.
  - viraptor 5y ago
    The idea of the race, bikes, and how we measure the whole thing is arbitrary to begin with :-)
- tomglynch 5y ago
  True, though if Wout won by the rules but Tom crossed the finish line first that is not a great outcome.
  - hiroprot 5y ago
    Given that they are not necessarily the same, perhaps more accurate to say "So who crossed the finish line first?" in your article? We know who won. As someone who has both won and lost bike races determined by photo finish, I enjoyed this article a lot. Well done sir!
sachkris 5y ago
Nice write-up. Instead of these photo-finish cameras, would a piezoelectric sensor strip on the road (plus perhaps a regular camera) be a better solution to judge the winner in such cases?
- martyvis 5y ago
  That would only work if the wheels were exactly the same diameter (assuming that the actual line is where the most forward part of the wheel crosses )
- Luc 5y ago
  But van Aert's front wheel was not even touching the road as he crossed the finish line...
- mod 5y ago
  No, because as I understand it we don't judge the winner from the base of the wheel, but rather the front of it.
- Workaccount2 5y ago
  I was thinking about this problem too, and realized that the photo-finish also provides placings for all the other contestants. Some other type of sensor might be able to more accurately place who was first, but could struggle greatly differentiating the pack of contestants behind them.
toast0 5y ago
Some thoughts from looking at amstel_Finishphoto_AGR21.png. a) in the horizontal axis, everything changes at 6 pixel intervals, I'm going to call those samples b) I count ten samples as the narrowest of the front tire at both the early samples and the later samples of both riders. (including the fringing). c) there's a two sample gap between the front of the front tire of the top rider and the bottom rider (pixels 835 - 840 for the top rider, and 823 - 828) d) there's also a two sample gap at the back of the front tire (pixels 355 - 361 for the top rider and pixels 343 - 348 for the bottom rider) I'm not invested enough to try to figure out other points of reference to compare, but it seems likely that if the riders were separated by two samples when their front tires entered the line of sampling, and also separated by two samples when their front tires left the line of sampling, that they were separated by two samples throughout that time. Since they would have crossed the (marked) finish line while their tires were being sampled, I'm comfyish saying the bottom rider was 2 samples behind the top at the finish line. If my calculation is right, each front tire took 80 samples to clear the line of sampling; and if it was 2000 samples per second, that's 0.04 seconds for the bikes to clear the camera; might that be enough time for the second bike to have been pushed forward and pulled back such that it may have won; I dunno. also e) now I've used up my evening time I had meant to do something else with :P
- tomglynch 5y ago
  Very good analysis. I'm just wondering if a 'bike throw' could cause a sudden acceleration and then deceleration both within the time the front wheel travelled over the line. Which could mean the rider in 2nd may have crossed the real finish line first. Though it's true that this does seem unlikely and therefore i'd also be comfy-ish with what you are suggestion.
  - toast0 5y ago
    If I hadn't forgotten where I put my physics hat, maybe we could figure out what sort of acceleration would be needed to get the bottom bike ahead of the top bike, assuming the top bike was traveling at constant velocity. If the front hubs were easier to distinguish, I'd have liked to compare those, but it didn't seem clear like the tires.
scotty79 5y ago
Or you could just change the rules and declare that the finish line is wherever the camera is pointed at and what's painted on the ground is just a rough indicator of where the finish line actually is. Or maybe rules are already exactly that?
- throwaway744678 5y ago
  Wouldn't it be a bit unfair for the competitors? They wouldn't have any way of knowing where the actual finish line would stand. Perhaps they could include some margin of error; if the photo is in that margin, the result would be a tie?
- adamjb 5y ago
  That is in fact what the UCI regulations say.
  - sverhagen 5y ago
    It's been maybe fifteen years since I read up on those rules, I assume some things changed, but there weren't much details on this then. Do you have some relevant quotes?
    - tomglynch 5y ago
      This is also what I thought when reading the rules. It does say the race if you can't tell by the eye is decided by the photo-finish. But from what I read at no point does it say, the finish is where the photo-finish points and the paint is just arbitrary.
helsinkiandrew 5y ago
I'd say that was a draw.
cycomanic 5y ago
I see on issue with this analysis, the use of the TV camera picture a the reference datum. However, that camera has likely many more issues than the finish line camera. While it looks like the red advertisement is aligned with the camera from that image I don't think this is necessarily the case. It depends on the height of the camera, the angle and possible distortions.
- tomglynch 5y ago
  While I've only inCluded that single image in my analysis, having a look at the video of the full race where they pass the finish line many times it is clear the red sign is aligned with the finish line.
  - cycomanic 5y ago
    That's not what I mean. You assume that the TV camera is perfectly aligned with the finish line, because that's how you determine the position of the advertisement relative to the line. However, if the TV camera is offset from the finish line, depending on height/focal length/orientation and aberrations of the camera, the line would appear offset relative to the advertisement. Therefore you determine the wrong position of the line compared to the advertisement. That would always be the same for the full video of the race, so watching the race will not change this.
    - cycomanic 5y ago
      I should say that it might not make a difference, but mainly to point out that one needs to be careful as to what exactly we use as our datum.
tsjq 5y ago
Too much work, IMO. Just give them both Gold medals.
- mariusor 5y ago
  For this particular race you get beer, not medals. I don't remember seeing medals in cycling outside of the Olympics.
FearNotDaniel 5y ago
As a child I was taught that sport should be "sportsmanlike". Perhaps in a situation like this, the real solution should be "I say, it's a draw, well done chaps, you have both proved to be at the top of your field! How remarkable that the result is so close that our best technology cannot even distinguish between the two of you. Well done everyone, what a great race, now let's all go to the pub and celebrate."
- cesis 5y ago
  That happens in Olympic Games https://www.olympic.org/news/double-gold-medal-joy-as-oleksiak-and-manuel-finish-in-dead-heat https://www.olympic.org/news/double-gold-medal-joy-as-oleksi...
  - doikor 5y ago
    This happens in swimming because of the tolerance of making an olympic spec pool. A good swimmer goes a bit over 2mm every 0.001s. The pools have 3cm tolerance meaning the lanes are not the exact same length (it would be crazy expensive to make pools to smaller tolerances) So to solve this they just don't measure beyond hundreds (no human can swim fast enough that the distance they travel within 0.01s could make a difference). And thus can not use photo finish either as again the lanes are not guaranteed to be the same length. https://interestingengineering.com/significant-digits-and-pool-tolerances-are-why-there-are-so-many-ties-in-swimming https://interestingengineering.com/significant-digits-and-po... edit: In other sports like running it is easy to have accurate track length as you just paint the lines after building the track so you can have it as accurate as you want (+photo finish). In swimming it just does not work like that.
    - xxs 5y ago
      Swimming is worse than that as the inner lanes have inherent advantage of less water drag as the waves bounce off the walls. Of course inner lanes are seeded with the fastest timings from the previous heat.
      - 5y ago
jrnvs 5y ago
Here's an interview with the photo operator, in Dutch: https://nos.nl/artikel/2377417-fotofinish-operator-amstel-gold-race-twijfelt-niet-je-ziet-dat-pidcock-te-laat-is https://nos.nl/artikel/2377417-fotofinish-operator-amstel-go... Interviewer: Is it possible that the photo was taken a wee bit before the black line? Photo operator: I doubt it... I doubt it because we really took a good look if it's all been set up correctly.
- tinus_hn 5y ago
  That’s obviously wrong because if they had pointed at the black line, the background of the picture wouldn’t have been the white part of the bar.
- sverhagen 5y ago
  I operated the photo finish at the Amstel Gold Race for a few years, in the early 2000s, as well as at many other races in the Netherlands, Belgium and Germany. We weren't a constant presence at that event, as the association liked it better to either bring in their own people, or rather full-time professionals like the company that does La Tour de France. My boss at that time later sold his timing business to the guy who operated the photo finish this year (the one being interviewed). While all folks involved here take great pride in their work, the alignment of the camera just never got the attention it clearly deserved. No one ever did the math and they just assumed the difference wasn't significant. Also, people just liked it better to align the camera on the white part of the finish line, since it greatly improves the contrast of the capture. I am sure the equipment has improved, but for a long time, the only thing you were concerned about was contrast, a sudden change in weather (lighting) was known to, at times, render the entire operation useless. Particularly since we were a small operation with only one (photo-finish) camera. Plenty of times I had to climb up ladders and vans to make eleventh hour adjustments to the equipment, with the contestants already in sight. I feel super bad for the guy. To his defense, the responsibility lies with the UCI officials. To their defense, they do not check up on details like this. Until now, that is. I remember at least one other time where the broadcast camera (they also tend to have one exactly on the finish line) seemed in disagreement with our "official" photo finish results. That time, a simple shrug did the trick: "hey, photo finish, you know".
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ernesth 5y ago
I assume the finish line should correspond to the scaffolding above the road that sports "Finish". https://www.tglyn.ch/blog/images/amstel_photofinish_camera_position.png https://www.tglyn.ch/blog/images/amstel_photofinish_camera_p... The computation by the author of the article indeed confirms this: https://www.tglyn.ch/blog/images/amstel_approx_line.png https://www.tglyn.ch/blog/images/amstel_approx_line.png My point is that it is the painted line that was not correctly placed rather than the camera.
- tomglynch 5y ago
  This would be a great question for the operator. Thanks for your input :)
mvanaltvorst 5y ago
Is it just me, or is it really obvious that Wout won? https://i.imgur.com/g78YNla.png https://i.imgur.com/g78YNla.png Each pixel column is a specific point in time. I added a few landmarks: when the front of the wheel passes the camera view, when the axis of the wheel passes the camera view, and when the end of the wheel passes the camera view. Blue for the top biker (Wout) and green for the bottom biker (Tom). Every single event happened earlier for Wout. Both wheels are the same diameter. Therefore, the entire period where the wheel intersected the camera view, Wout's wheel was ahead. Including the exact period where Wout passed the actual finish line. If Tom would have passed Wout, you would expect that the bottom wheel would be more "squeezed" such that the end of Tom's wheel would have passed the camera line earlier than Wout. Same for the other landmark (centre of wheel). You can add more landmarks if you want (e.g. approximate when the wheel passes for 25% and for 75%), but it should be clear by pure margin that Wout had the lead for the whole duration where the front wheels passed the camera view. Pretty much all the computation in this article was unnecessary. Amstel gold made the good call, though I agree that it was probably more luck.
- rockdoe 5y ago
  This analysis assumes the camera was aligned perfectly parallel to the finish line, but offset from it. Unfortunately, there's no reason to assume this was true. Almost the opposite! If the operator did set up the camera correctly initially, and we know the far end ended up pointing to the wrong panel (got a knock?), this makes it more likely it was skewed so as to advantage the most distant rider. And that was Van Aert.
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  - mannykannot 5y ago
    Supporting evidence for your point comes, I think, from the fact that, for each bicycle, the left end of the handlebars appears ahead of the right one - meaning that it crossed the plane of the camera view first. I don't think the wheels could have been noticably misaligned from straight ahead here, could they? - in which case, this would imply that the camera plane is skewed as you suggest. If this is correct, then it suggests a way to estimate, and correct for, the skew, as we have other photos and videos showing approxinately how far the riders were from each other and from the camera, as well as their trajectories as they crossed the line.
mhandley 5y ago
One other possibility is that the camera was positioned in the correct place, but was angled slightly to the left with respect to the line, rather than being exactly parallel with the line. I don't know how they set up these cameras to ensure they're parallel with the line, but this seems at least as likely as aligning the camera parallel but in the wrong place. I'm not sure how you'd be able to tell from the images though, but it would make a much bigger difference to the actual result.
Havoc 5y ago
Somewhat amazing that this can’t be determined reliably. As far as physics problems go it seems reasonably tame compared to other challenges out there
MR4D 5y ago
Fascinating article, and great to see a problem solver at work. However, I question humanity’s sanity when we declare a winner in a 216.75km long race by someone who (possibly) won by 0.016 seconds (and poorly declared either way from the article). At what point do races become a tie instead of 1st/2nd ? Just because we can doesn’t mean we should. I mean, if we had a camera that could take 350,000 photos per second does that mean we should use it to declare the winner? I remember this issue came up in swimming a few years ago, and people were arguing that the timing measurement was finer than the tolerance for error of the measurement of pressure on the pad. We still talk about that race venue today: https://www.theringer.com/2020/7/29/21345181/milorad-cavic-michael-phelps-2008-olympics-beijing-100-butterfly-conspiracy https://www.theringer.com/2020/7/29/21345181/milorad-cavic-m... This article seems to make the argument quite well: https://olympics.time.com/2012/07/27/technologys-touch-how-a-photo-finish-in-the-olympic-pool-gets-resolved/ https://olympics.time.com/2012/07/27/technologys-touch-how-a...
- sverhagen 5y ago
  I don't think the competition really is: who's the fastest in a 216km race? Rather: who's strong enough to endure a 200km tour, and then still have the energy for a 16km race? I say this half jokingly only.
  - vbsteven 5y ago
    That's the beauty of cycling isn't it? Sometimes the race-winning move is decided in a team car 150km from the line, and the next day it comes down to millimeters. This unpredictability is what keeps most viewers hooked to their TV sets for 6 hours on big race days.
    - usrusr 5y ago
      Sometimes, as in when it happens, people might still be talking about it decades later (I'm only slightly exaggerating) But all spectator sports seem to gain much their appeal from the imperfections that make them special. In road cycling, it's the imbalance of many hours of what computer gamers would call mostly cooperative PvE serving as a buildup for the few seconds of the finish (unless it's a solo, which is super attractive for the audience because it's rare, but would be rather boring if it wasn't).
getlawgdon 5y ago
I'm deeply familiar with FAT andamera systems in track and field. I often wonder if they are a relic but in track the timing can be trickier due to location of the torso. Wouldn't a transponder on a each headtube in the race potentially work better? They could talk communicate with sensors all around and in the finish line.
kingosticks 5y ago
There's a arguably better, higher level writeup at https://cyclingtips.com/2021/04/making-sense-of-the-controversial-photo-finish-at-amstel-gold/ https://cyclingtips.com/2021/04/making-sense-of-the-controve... which concludes: > The black line is a visual approximation of the placement of the finish, but the image from the photo finish camera is the true arbiter of the result – not the other way around. It’s technical and it’s a bit confusing, but it’s clear-cut and the riders and officials are playing the same game with the same known set of rules. > According to UCI regulations, the photo finish verdict is final, because the finish line is what the photo finish says it is. Which makes most of the detective work here sadly pointless. Pidcock probably didn't need to tweet his take, in the same way he didn't need to post that ridiculous bogus 5k time! https://www.rouleur.cc/blogs/the-rouleur-journal/the-column-tom-pidcock-5k-time-proves-he-ll-win-the-tour-de-france https://www.rouleur.cc/blogs/the-rouleur-journal/the-column-...
- Invictus0 5y ago
  If there are supposed to be two photo finish cameras, how can the photo finish be the true arbiter? The two cameras cannot possibly be perfectly aligned.
  - kingosticks 5y ago
    I'm not an expert but the UCI document labels it as "1 main camera, 1 opposite". So I would guess the "main" camera is the source of truth and the other is a backup? Either way, presumably both cameras ideally need to be aligned to the line as stated. That should be possible and perfect alignment between the two cameras isn't required. I can't see anywhere that it states the two cameras actually need to agree, isn't it fine providing one of them is used consistently.
    - deleted 5y ago
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- bagacrap 5y ago
  this. Also the camera is intentionally not aligned to the black strip on the tarmac as tires are black and this would make it hard to see them.
PaulHoule 5y ago
I've wondered what you'd get if you put a "photo finish" camera on the side of a car. The perspective would be out of whack (e.g. a 10 m long object 20 m away looks the same length as a 10 m long object 2000 m away) but it would be a much cheaper sensor than what Google uses for street view.
- HALtheWise 5y ago
  I would be excited to see someone try that, since it would produce an image that is effectively a parallel viewpoint in one axis and a pinhole camera in the other. I doubt it would be cheaper than Google's street view cameras, though, since standard cameras and lenses are commodity equipment.
  - PaulHoule 5y ago
    I think I will. An ordinary camera would work if mounted rigidly to the car, you could shoot a video and then take out the center line after the fact. 55 miles/hour is about 80 ft/sec so the horizontal resolution is a little bit more than a foot with a 60 fps video, you could make out houses but not read house numbers. I think most webcams have a low-level interface that would let you read out part of the display without reading the rest so getting a better frame rate could be done at low cost too. I think I'm going to try taking pictures of clouds first...
    - tomglynch 5y ago
      Come to think of it, what you're describing is pretty similar to a panorama photo
      - PaulHoule 5y ago
        There is a whole family of "algorithms" for putting together a sequence of images, for instance, if a camera at the side of the road took a slice of pixels at a 45 degree angle you would get a picture of any car (esp license plate) or person who went by, but you would not get a video showing what they did in any detail. Panorama mode is trying to make something that looks like "a good image", you would want to keep "tack sharp" if the source material is "tack sharp." If you have 1000s of photographs of a scene you can reference them to each other and build a 3-d model and then synthesize many images you might want to see but it won't be "tack sharp" it will be a video game.
dekhn 5y ago
Time differences like this are insignificant.
fotta 5y ago
I used to work with these line-scan photo finish camera systems (we used FinishLynx) timing track meets. This error is pretty comical to me because aligning the camera is the first thing we do after putting the camera up and looking at their images, it's pretty clear it wasn't aligned properly. The cameras can auto-align, but we didn't trust it and manually aligned it, but I'm wondering if maybe the event organizers auto-aligned and didn't bother to check? The cameras are mounted on a motorized base that can move in 3 dimensions with very fine precision [0]. In the OP, you can see the event organizers have a black line across the finish on a white base. In order to manually align it you just have someone run back and forth across the line and move the camera with the computer until you pick up the very left edge of the black line, which is very clear because you can see the ground change from black to white in the image (or vice versa depending on where you start). We also used to always put a white piece of wood behind the line so that the images would always have a white background. This makes it so much easier to detect the edge of a torso when clicking on a person to indicate their time. In the OP, if their camera was aligned correctly, red would've been a tough background color. Also a black line is questionable. I would've had a white line on black base for the same reasons. [0] https://www.finishlynx.com/product/accessories/camera-mountings/remote-camera-positioner/ https://www.finishlynx.com/product/accessories/camera-mounti...
xpe 5y ago
In addition to the technological factors here (optics), think about the biological timing of the riders. Wout van Aert picked the right time to accelerate and win -- from the front! He won even with a significant aerodynamic disadvantage. Wout!!! > According to UCI regulations, the photo finish verdict is final, because the finish line is what the photo finish says it is. https://cyclingtips.com/2021/04/making-sense-of-the-controversial-photo-finish-at-amstel-gold/ https://cyclingtips.com/2021/04/making-sense-of-the-controve...
Rastonbury 5y ago
Any reason why the single pixel wide capture approach is used? Seems very prone to operator setup error. It has to be exact at the finish line and exactly parallel to the line and there's no easy way of knowing if it was setup correctly after the face. Wouldn't it be better to set up multiple high speed cameras at different angles
- Doxin 5y ago
  High speed cameras produce significantly more output data, which makes them more expensive I'd have to imagine. Not to mention a high speed camera misaligned on the finish is going to produce similarly skewed results. Anything not happening exactly along the optical axis is getting distorted by perspective. At least a line camera doesn't pretend to have accurate information on anything except the line you aim it at.

504 points by tomglynch 5y ago

OP here. I think the spoke movement is probably the most likely to be able to work out who reached the actual finish first. That is based on the spoke patterns in this image: http://tglyn.ch/blog/images/amstel_Finishphoto_AGR21.png http://tglyn.ch/blog/images/amstel_Finishphoto_AGR21.png The curve of the spokes should mean we can determine the distance the rider has traveled after the photo-finish camera. I cover my other ideas in the 'Further research required section' about 75% of the way down the article. If you have any further suggestions please let me know. Tom

jhgb 5y ago
> having it in the wrong spot means we may never know if Tom Pidcock's extra speed would have allowed him to make up the small distance in the final 26.86cm. Isn't it possible to extrapolate the movement from the last few frames of the image sequence?
- tomglynch 5y ago
  Potentially - do you mean via the video or the photo-finish image? I've suggested in the article looking at when the wheel reaches 98% of the full height which I think is along the lines of what you're saying.
  - jhgb 5y ago
    I meant the photo-finish cameras, but nevermind, I forgot how these things worked. But I would expect high-speed 2D cameras being available today at the finish line as well.
masswerk 5y ago
I think, the spokes are a good approach, since these are actually objects recorded in time. However, I think @gorgoiler [1] has made a valid point regarding the intersection of the "finish plane" and the plane recorded by the camera. (On the photo shown on your blog, the camera appears to be mounted slightly behind the finish line, thus, intersecting the "finish plane" at the ideal height, should point to just before the finish line at ground level. But there isn’t sufficient information in the photo to measure such a minimal angle, or to confirm, if there's any at all.) [1] https://news.ycombinator.com/item?id=26977975 https://news.ycombinator.com/item?id=26977975
eCa 5y ago
Very nice write-up, it was a fun race to watch. On your future research, alternative 1: Instead of only looking at the width of the wheel, what about looking at the height/width ratio? The quicker wheel ought to be relatively more ”squished” horizontally. On the other hand, with the tight margins involved, it might be that the ratios are not comparable due to the fact that they are not the same distance from the camera.
mnw21cam 5y ago
The shape of the curves of the spokes doesn't depend on the speed. If you take the picture of the wheel, and fix the aspect ratio so that it is circular, then the spokes will have a curve independent of the speed of the wheel. Speed determination is purely based on the aspect ratio of the entire wheel. To reason on why this might be true - consider that the bottom of the wheel is stationary, and the top of the wheel is moving at twice the speed. This is the case regardless of the speed of the wheel. If you rolled the wheel past the camera really slowly, the entire wheel would be stretched out horizontally, but the spokes would all be in the same arrangement. The reason for this is that the camera is a fixed position line scan where the variable is time only. If we switch to thinking about standard video cameras with a rolling shutter, then these have a line scan where the variable is time and space - that is, the camera samples a scan that is moving at a known speed. If you have a video with a camera like this of helicopter blades, for instance, then you can determine the blade rotation speed from a single frame. But with this finish camera, that doesn't work. So, to determine speed, the best possible action is to pick two points on the rigid body that is moving, and time how long it takes to pass the recording line. The further apart these points are, the more accurate the average speed determination will be. The trade-off for this is that the speed measurement will be the average between the time the first point and the second point passes the recording line, and we are only interested in the average speed at the point the front of the bike passes the line. What we can show however, as pointed out elsewhere[0], is that one bike was in front of the other when the front of the wheel, the hub of the wheel, and the back of the wheel passed the recording point. When the back of the wheel passed the recording point, the front of the wheel definitely passed the actual finish line, so assuming the two wheels are the same size then the front of that wheel passed the finish line before the other one. [0] https://news.ycombinator.com/item?id=26978621 https://news.ycombinator.com/item?id=26978621
- tomglynch 5y ago
  Great comment! Super informative and something I had not properly thought about. But you're totally right, curvature of the spokes is based only on the fact it's rolling past the camera, and two wheels rolling at different speeds will result in the same spoke pattern.

tgtweak 5y ago

Taking "Internet Detective" to new and exotic levels.

tomglynch 5y ago
Haha thank you - which part stood out to you?
- disillusioned 5y ago
  Bro, literally all of it. What a great piece. Down to guesstimating the tire sizes, tracking down the line width, accounting for road camber, etc. Really enjoyed this.
  - tomglynch 5y ago
    Haha cheers! Enjoyed every moment of it (though I did spend quite a while on it all!)

deanpea 5y ago

Very interesting write up. Given the price of photo-finish cameras, I wonder if there’s a solution with slow motion cameras which could provide some margin for error as well as a better spectacle for viewers?

tomglynch 5y ago
Yeah true - it would be interesting if one of the super slow mo cameras they use in sports would be as good at determining the winner.
- comex 5y ago
  Well, there are slow mo cameras that go well over the 2,000 or 3,500 FPS mentioned in the article. If oriented the same way, they would provide a strict superset of the information of a strip photography camera, since you could recover the strip photo by just extracting one column from successive frames of the video. It doesn’t seem like the price is even particularly different. I’m not an expert, though, just judging based on Google results. Maybe there is some obstacle I’m not thinking of.
rocqua 5y ago
Slow mo camera's produce too much data to run continuously. These camera's are used to determine the entire finishing order. They need to be running constantly.
- ska 5y ago
  You could filter a lot of it out automatically - might be doable these days.

jrudolph 5y ago

Awesome research. I have similar quibbles about photo finish cameras in sports and written about them [0]. There are usually tons of rules in sport about the equipment, the Race course etc . but how exactly the finish needs to be set up is often vague. In this case it was an alignment issue at fault. But the next problem is the arbitrary resolution finish cameras work at. How wide is the pixel slot? This can be the difference between calling a tie or a small margin. [0] https://www.rowinginmotion.com/thoughts-fairness-rowing/ https://www.rowinginmotion.com/thoughts-fairness-rowing/

tomglynch 5y ago
Yeah the UCI rules for photo finish seem very vague, and also don't seem enforced. I haven't used a photo-finish camera myself but it seems to me the tech behind these is quite dated, the shots from the 1960s are almost as good except for the frame rate and number of pixels. Perhaps there is a better way.

xmprt 5y ago

This was a really good writeup. I thought for sure there would be no way to salvage it after you mentioned how they messed up but then you talked about using the curvature of the spokes and the width of the wheels in the photo finish to figure out how the wheels were spinning and it blew my mind.

abel_ 5y ago

I think the distortion of the video-finish camera should be considered when making these estimates. There's quite a lot of it happening in the shot. Narrowing down the specific camera intrinsic parameters may be a challenge. The EXIF data of the original footage might be fruitful. It might also be possible to undistort using some assumptions on colinear points in the video (i.e., the finish line and signs should have straight lines).

tomglynch 5y ago
Exif data is a good suggestion - I'll see what I've got EDIT: nah nothing interesting there. It may have been stripped when they emailed it to me?
lostlogin 5y ago
> It might also be possible to undistort. It might be possible to res it right up using that new photoshop feature. A joke obviously...

gorgoiler 5y ago

The “finish line” could be thought of as a two dimensional plane. The winner is the first person to touch or pass through the plane. If you’re painting a line then the “finish line” is where that plane touches the ground. For other races it might be a piece of tape held at chest height — the part of the body that usually goes through the plane first. When the competitors are bicycles then they all the same height — the middles of the front wheels are all the same height off the ground, something on the order of 400mm. The finish line is floating about a foot off the ground. The specialist streak camera photographs objects passing through a 2D plane. Ideally you would have that plane aligned vertically so that the finish plane and the camera plane were the same. If for some reason you couldn’t do that — let’s say the camera could only be placed a few feet in front of the finish line so as to see around an object — then you would have to arbitrarily angle the camera plane to intersect the finish plane. The intersection of these two planes will give you the “finish line”. For a bicycle race, do you set it up so that the finish line is on the ground, or floating 400mm above the ground? If you do the latter then the projection of the camera plane into the road will indeed give a line that stops short of the finish plane, but that’s irrelevant — the actual finish line at the middle of the front wheel is in the correct place. I think the article assumes the former when the organisers did the latter?

tomglynch 5y ago
Ah this is an interesting thought though I don't think this is what the organisers were trying to do. Or if they are, it does not match up with what they are meant to do as per the UCI specs (the UCI is the international cycling governing body). In another comment I was discussing the tech being somewhat outdated - perhaps your suggestion is part of the solution. Would two cameras on different planes result in more accurate results?
- gorgoiler 5y ago
  It’s probably quite hard to make an orthographic streak camera that is pointing vertically down in the same plane as the finish, but that seems like the optimal solution. Moreover, if the camera is used to identify the times and finish positions of all the riders, it’s probably quite hard to identify them from above. Perhaps a streak video synchronised with TV footage would be convincing? How about a prismatic laser and fog machine at the finish? It’ll look like an 80s rave but the streak camera will clearly show where the finish is.

runningmike 5y ago

Great research! But van Aart is the right winner. The photo finish picture is stated s the official result. Every athlete knows that, despite alignment errors of the equipment.

djmips 5y ago
Exactly. It's a bit arbitrary but it's the final call.
- viraptor 5y ago
  The idea of the race, bikes, and how we measure the whole thing is arbitrary to begin with :-)
tomglynch 5y ago
True, though if Wout won by the rules but Tom crossed the finish line first that is not a great outcome.
- hiroprot 5y ago
  Given that they are not necessarily the same, perhaps more accurate to say "So who crossed the finish line first?" in your article? We know who won. As someone who has both won and lost bike races determined by photo finish, I enjoyed this article a lot. Well done sir!

sachkris 5y ago

Nice write-up. Instead of these photo-finish cameras, would a piezoelectric sensor strip on the road (plus perhaps a regular camera) be a better solution to judge the winner in such cases?

martyvis 5y ago
That would only work if the wheels were exactly the same diameter (assuming that the actual line is where the most forward part of the wheel crosses )
Luc 5y ago
But van Aert's front wheel was not even touching the road as he crossed the finish line...
mod 5y ago
No, because as I understand it we don't judge the winner from the base of the wheel, but rather the front of it.
Workaccount2 5y ago
I was thinking about this problem too, and realized that the photo-finish also provides placings for all the other contestants. Some other type of sensor might be able to more accurately place who was first, but could struggle greatly differentiating the pack of contestants behind them.

toast0 5y ago

Some thoughts from looking at amstel_Finishphoto_AGR21.png. a) in the horizontal axis, everything changes at 6 pixel intervals, I'm going to call those samples b) I count ten samples as the narrowest of the front tire at both the early samples and the later samples of both riders. (including the fringing). c) there's a two sample gap between the front of the front tire of the top rider and the bottom rider (pixels 835 - 840 for the top rider, and 823 - 828) d) there's also a two sample gap at the back of the front tire (pixels 355 - 361 for the top rider and pixels 343 - 348 for the bottom rider) I'm not invested enough to try to figure out other points of reference to compare, but it seems likely that if the riders were separated by two samples when their front tires entered the line of sampling, and also separated by two samples when their front tires left the line of sampling, that they were separated by two samples throughout that time. Since they would have crossed the (marked) finish line while their tires were being sampled, I'm comfyish saying the bottom rider was 2 samples behind the top at the finish line. If my calculation is right, each front tire took 80 samples to clear the line of sampling; and if it was 2000 samples per second, that's 0.04 seconds for the bikes to clear the camera; might that be enough time for the second bike to have been pushed forward and pulled back such that it may have won; I dunno. also e) now I've used up my evening time I had meant to do something else with :P

tomglynch 5y ago
Very good analysis. I'm just wondering if a 'bike throw' could cause a sudden acceleration and then deceleration both within the time the front wheel travelled over the line. Which could mean the rider in 2nd may have crossed the real finish line first. Though it's true that this does seem unlikely and therefore i'd also be comfy-ish with what you are suggestion.
- toast0 5y ago
  If I hadn't forgotten where I put my physics hat, maybe we could figure out what sort of acceleration would be needed to get the bottom bike ahead of the top bike, assuming the top bike was traveling at constant velocity. If the front hubs were easier to distinguish, I'd have liked to compare those, but it didn't seem clear like the tires.

scotty79 5y ago

Or you could just change the rules and declare that the finish line is wherever the camera is pointed at and what's painted on the ground is just a rough indicator of where the finish line actually is. Or maybe rules are already exactly that?

throwaway744678 5y ago
Wouldn't it be a bit unfair for the competitors? They wouldn't have any way of knowing where the actual finish line would stand. Perhaps they could include some margin of error; if the photo is in that margin, the result would be a tie?
adamjb 5y ago
That is in fact what the UCI regulations say.
- sverhagen 5y ago
  It's been maybe fifteen years since I read up on those rules, I assume some things changed, but there weren't much details on this then. Do you have some relevant quotes?
  - tomglynch 5y ago
    This is also what I thought when reading the rules. It does say the race if you can't tell by the eye is decided by the photo-finish. But from what I read at no point does it say, the finish is where the photo-finish points and the paint is just arbitrary.

helsinkiandrew 5y ago

I'd say that was a draw.

cycomanic 5y ago

I see on issue with this analysis, the use of the TV camera picture a the reference datum. However, that camera has likely many more issues than the finish line camera. While it looks like the red advertisement is aligned with the camera from that image I don't think this is necessarily the case. It depends on the height of the camera, the angle and possible distortions.

tomglynch 5y ago
While I've only inCluded that single image in my analysis, having a look at the video of the full race where they pass the finish line many times it is clear the red sign is aligned with the finish line.
- cycomanic 5y ago
  That's not what I mean. You assume that the TV camera is perfectly aligned with the finish line, because that's how you determine the position of the advertisement relative to the line. However, if the TV camera is offset from the finish line, depending on height/focal length/orientation and aberrations of the camera, the line would appear offset relative to the advertisement. Therefore you determine the wrong position of the line compared to the advertisement. That would always be the same for the full video of the race, so watching the race will not change this.
  - cycomanic 5y ago
    I should say that it might not make a difference, but mainly to point out that one needs to be careful as to what exactly we use as our datum.

tsjq 5y ago

Too much work, IMO. Just give them both Gold medals.

mariusor 5y ago
For this particular race you get beer, not medals. I don't remember seeing medals in cycling outside of the Olympics.

FearNotDaniel 5y ago

As a child I was taught that sport should be "sportsmanlike". Perhaps in a situation like this, the real solution should be "I say, it's a draw, well done chaps, you have both proved to be at the top of your field! How remarkable that the result is so close that our best technology cannot even distinguish between the two of you. Well done everyone, what a great race, now let's all go to the pub and celebrate."

cesis 5y ago
That happens in Olympic Games https://www.olympic.org/news/double-gold-medal-joy-as-oleksiak-and-manuel-finish-in-dead-heat https://www.olympic.org/news/double-gold-medal-joy-as-oleksi...
- doikor 5y ago
  This happens in swimming because of the tolerance of making an olympic spec pool. A good swimmer goes a bit over 2mm every 0.001s. The pools have 3cm tolerance meaning the lanes are not the exact same length (it would be crazy expensive to make pools to smaller tolerances) So to solve this they just don't measure beyond hundreds (no human can swim fast enough that the distance they travel within 0.01s could make a difference). And thus can not use photo finish either as again the lanes are not guaranteed to be the same length. https://interestingengineering.com/significant-digits-and-pool-tolerances-are-why-there-are-so-many-ties-in-swimming https://interestingengineering.com/significant-digits-and-po... edit: In other sports like running it is easy to have accurate track length as you just paint the lines after building the track so you can have it as accurate as you want (+photo finish). In swimming it just does not work like that.
  - xxs 5y ago
    Swimming is worse than that as the inner lanes have inherent advantage of less water drag as the waves bounce off the walls. Of course inner lanes are seeded with the fastest timings from the previous heat.
    - 5y ago

jrnvs 5y ago

Here's an interview with the photo operator, in Dutch: https://nos.nl/artikel/2377417-fotofinish-operator-amstel-gold-race-twijfelt-niet-je-ziet-dat-pidcock-te-laat-is https://nos.nl/artikel/2377417-fotofinish-operator-amstel-go... Interviewer: Is it possible that the photo was taken a wee bit before the black line? Photo operator: I doubt it... I doubt it because we really took a good look if it's all been set up correctly.

tinus_hn 5y ago
That’s obviously wrong because if they had pointed at the black line, the background of the picture wouldn’t have been the white part of the bar.
sverhagen 5y ago
I operated the photo finish at the Amstel Gold Race for a few years, in the early 2000s, as well as at many other races in the Netherlands, Belgium and Germany. We weren't a constant presence at that event, as the association liked it better to either bring in their own people, or rather full-time professionals like the company that does La Tour de France. My boss at that time later sold his timing business to the guy who operated the photo finish this year (the one being interviewed). While all folks involved here take great pride in their work, the alignment of the camera just never got the attention it clearly deserved. No one ever did the math and they just assumed the difference wasn't significant. Also, people just liked it better to align the camera on the white part of the finish line, since it greatly improves the contrast of the capture. I am sure the equipment has improved, but for a long time, the only thing you were concerned about was contrast, a sudden change in weather (lighting) was known to, at times, render the entire operation useless. Particularly since we were a small operation with only one (photo-finish) camera. Plenty of times I had to climb up ladders and vans to make eleventh hour adjustments to the equipment, with the contestants already in sight. I feel super bad for the guy. To his defense, the responsibility lies with the UCI officials. To their defense, they do not check up on details like this. Until now, that is. I remember at least one other time where the broadcast camera (they also tend to have one exactly on the finish line) seemed in disagreement with our "official" photo finish results. That time, a simple shrug did the trick: "hey, photo finish, you know".

deleted 5y ago

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ernesth 5y ago

I assume the finish line should correspond to the scaffolding above the road that sports "Finish". https://www.tglyn.ch/blog/images/amstel_photofinish_camera_position.png https://www.tglyn.ch/blog/images/amstel_photofinish_camera_p... The computation by the author of the article indeed confirms this: https://www.tglyn.ch/blog/images/amstel_approx_line.png https://www.tglyn.ch/blog/images/amstel_approx_line.png My point is that it is the painted line that was not correctly placed rather than the camera.

tomglynch 5y ago
This would be a great question for the operator. Thanks for your input :)

mvanaltvorst 5y ago

Is it just me, or is it really obvious that Wout won? https://i.imgur.com/g78YNla.png https://i.imgur.com/g78YNla.png Each pixel column is a specific point in time. I added a few landmarks: when the front of the wheel passes the camera view, when the axis of the wheel passes the camera view, and when the end of the wheel passes the camera view. Blue for the top biker (Wout) and green for the bottom biker (Tom). Every single event happened earlier for Wout. Both wheels are the same diameter. Therefore, the entire period where the wheel intersected the camera view, Wout's wheel was ahead. Including the exact period where Wout passed the actual finish line. If Tom would have passed Wout, you would expect that the bottom wheel would be more "squeezed" such that the end of Tom's wheel would have passed the camera line earlier than Wout. Same for the other landmark (centre of wheel). You can add more landmarks if you want (e.g. approximate when the wheel passes for 25% and for 75%), but it should be clear by pure margin that Wout had the lead for the whole duration where the front wheels passed the camera view. Pretty much all the computation in this article was unnecessary. Amstel gold made the good call, though I agree that it was probably more luck.

rockdoe 5y ago
This analysis assumes the camera was aligned perfectly parallel to the finish line, but offset from it. Unfortunately, there's no reason to assume this was true. Almost the opposite! If the operator did set up the camera correctly initially, and we know the far end ended up pointing to the wrong panel (got a knock?), this makes it more likely it was skewed so as to advantage the most distant rider. And that was Van Aert.
- deleted 5y ago
  [deleted]
- mannykannot 5y ago
  Supporting evidence for your point comes, I think, from the fact that, for each bicycle, the left end of the handlebars appears ahead of the right one - meaning that it crossed the plane of the camera view first. I don't think the wheels could have been noticably misaligned from straight ahead here, could they? - in which case, this would imply that the camera plane is skewed as you suggest. If this is correct, then it suggests a way to estimate, and correct for, the skew, as we have other photos and videos showing approxinately how far the riders were from each other and from the camera, as well as their trajectories as they crossed the line.

mhandley 5y ago

One other possibility is that the camera was positioned in the correct place, but was angled slightly to the left with respect to the line, rather than being exactly parallel with the line. I don't know how they set up these cameras to ensure they're parallel with the line, but this seems at least as likely as aligning the camera parallel but in the wrong place. I'm not sure how you'd be able to tell from the images though, but it would make a much bigger difference to the actual result.

Havoc 5y ago

Somewhat amazing that this can’t be determined reliably. As far as physics problems go it seems reasonably tame compared to other challenges out there

MR4D 5y ago

Fascinating article, and great to see a problem solver at work. However, I question humanity’s sanity when we declare a winner in a 216.75km long race by someone who (possibly) won by 0.016 seconds (and poorly declared either way from the article). At what point do races become a tie instead of 1st/2nd ? Just because we can doesn’t mean we should. I mean, if we had a camera that could take 350,000 photos per second does that mean we should use it to declare the winner? I remember this issue came up in swimming a few years ago, and people were arguing that the timing measurement was finer than the tolerance for error of the measurement of pressure on the pad. We still talk about that race venue today: https://www.theringer.com/2020/7/29/21345181/milorad-cavic-michael-phelps-2008-olympics-beijing-100-butterfly-conspiracy https://www.theringer.com/2020/7/29/21345181/milorad-cavic-m... This article seems to make the argument quite well: https://olympics.time.com/2012/07/27/technologys-touch-how-a-photo-finish-in-the-olympic-pool-gets-resolved/ https://olympics.time.com/2012/07/27/technologys-touch-how-a...

sverhagen 5y ago
I don't think the competition really is: who's the fastest in a 216km race? Rather: who's strong enough to endure a 200km tour, and then still have the energy for a 16km race? I say this half jokingly only.
- vbsteven 5y ago
  That's the beauty of cycling isn't it? Sometimes the race-winning move is decided in a team car 150km from the line, and the next day it comes down to millimeters. This unpredictability is what keeps most viewers hooked to their TV sets for 6 hours on big race days.
  - usrusr 5y ago
    Sometimes, as in when it happens, people might still be talking about it decades later (I'm only slightly exaggerating) But all spectator sports seem to gain much their appeal from the imperfections that make them special. In road cycling, it's the imbalance of many hours of what computer gamers would call mostly cooperative PvE serving as a buildup for the few seconds of the finish (unless it's a solo, which is super attractive for the audience because it's rare, but would be rather boring if it wasn't).

getlawgdon 5y ago

I'm deeply familiar with FAT andamera systems in track and field. I often wonder if they are a relic but in track the timing can be trickier due to location of the torso. Wouldn't a transponder on a each headtube in the race potentially work better? They could talk communicate with sensors all around and in the finish line.

kingosticks 5y ago

There's a arguably better, higher level writeup at https://cyclingtips.com/2021/04/making-sense-of-the-controversial-photo-finish-at-amstel-gold/ https://cyclingtips.com/2021/04/making-sense-of-the-controve... which concludes: > The black line is a visual approximation of the placement of the finish, but the image from the photo finish camera is the true arbiter of the result – not the other way around. It’s technical and it’s a bit confusing, but it’s clear-cut and the riders and officials are playing the same game with the same known set of rules. > According to UCI regulations, the photo finish verdict is final, because the finish line is what the photo finish says it is. Which makes most of the detective work here sadly pointless. Pidcock probably didn't need to tweet his take, in the same way he didn't need to post that ridiculous bogus 5k time! https://www.rouleur.cc/blogs/the-rouleur-journal/the-column-tom-pidcock-5k-time-proves-he-ll-win-the-tour-de-france https://www.rouleur.cc/blogs/the-rouleur-journal/the-column-...

Invictus0 5y ago
If there are supposed to be two photo finish cameras, how can the photo finish be the true arbiter? The two cameras cannot possibly be perfectly aligned.
- kingosticks 5y ago
  I'm not an expert but the UCI document labels it as "1 main camera, 1 opposite". So I would guess the "main" camera is the source of truth and the other is a backup? Either way, presumably both cameras ideally need to be aligned to the line as stated. That should be possible and perfect alignment between the two cameras isn't required. I can't see anywhere that it states the two cameras actually need to agree, isn't it fine providing one of them is used consistently.
  - deleted 5y ago
    [deleted]
bagacrap 5y ago
this. Also the camera is intentionally not aligned to the black strip on the tarmac as tires are black and this would make it hard to see them.

PaulHoule 5y ago

I've wondered what you'd get if you put a "photo finish" camera on the side of a car. The perspective would be out of whack (e.g. a 10 m long object 20 m away looks the same length as a 10 m long object 2000 m away) but it would be a much cheaper sensor than what Google uses for street view.

HALtheWise 5y ago
I would be excited to see someone try that, since it would produce an image that is effectively a parallel viewpoint in one axis and a pinhole camera in the other. I doubt it would be cheaper than Google's street view cameras, though, since standard cameras and lenses are commodity equipment.
- PaulHoule 5y ago
  I think I will. An ordinary camera would work if mounted rigidly to the car, you could shoot a video and then take out the center line after the fact. 55 miles/hour is about 80 ft/sec so the horizontal resolution is a little bit more than a foot with a 60 fps video, you could make out houses but not read house numbers. I think most webcams have a low-level interface that would let you read out part of the display without reading the rest so getting a better frame rate could be done at low cost too. I think I'm going to try taking pictures of clouds first...
  - tomglynch 5y ago
    Come to think of it, what you're describing is pretty similar to a panorama photo
    - PaulHoule 5y ago
      There is a whole family of "algorithms" for putting together a sequence of images, for instance, if a camera at the side of the road took a slice of pixels at a 45 degree angle you would get a picture of any car (esp license plate) or person who went by, but you would not get a video showing what they did in any detail. Panorama mode is trying to make something that looks like "a good image", you would want to keep "tack sharp" if the source material is "tack sharp." If you have 1000s of photographs of a scene you can reference them to each other and build a 3-d model and then synthesize many images you might want to see but it won't be "tack sharp" it will be a video game.

dekhn 5y ago

Time differences like this are insignificant.

fotta 5y ago

I used to work with these line-scan photo finish camera systems (we used FinishLynx) timing track meets. This error is pretty comical to me because aligning the camera is the first thing we do after putting the camera up and looking at their images, it's pretty clear it wasn't aligned properly. The cameras can auto-align, but we didn't trust it and manually aligned it, but I'm wondering if maybe the event organizers auto-aligned and didn't bother to check? The cameras are mounted on a motorized base that can move in 3 dimensions with very fine precision [0]. In the OP, you can see the event organizers have a black line across the finish on a white base. In order to manually align it you just have someone run back and forth across the line and move the camera with the computer until you pick up the very left edge of the black line, which is very clear because you can see the ground change from black to white in the image (or vice versa depending on where you start). We also used to always put a white piece of wood behind the line so that the images would always have a white background. This makes it so much easier to detect the edge of a torso when clicking on a person to indicate their time. In the OP, if their camera was aligned correctly, red would've been a tough background color. Also a black line is questionable. I would've had a white line on black base for the same reasons. [0] https://www.finishlynx.com/product/accessories/camera-mountings/remote-camera-positioner/ https://www.finishlynx.com/product/accessories/camera-mounti...

xpe 5y ago

In addition to the technological factors here (optics), think about the biological timing of the riders. Wout van Aert picked the right time to accelerate and win -- from the front! He won even with a significant aerodynamic disadvantage. Wout!!! > According to UCI regulations, the photo finish verdict is final, because the finish line is what the photo finish says it is. https://cyclingtips.com/2021/04/making-sense-of-the-controversial-photo-finish-at-amstel-gold/ https://cyclingtips.com/2021/04/making-sense-of-the-controve...

Rastonbury 5y ago

Any reason why the single pixel wide capture approach is used? Seems very prone to operator setup error. It has to be exact at the finish line and exactly parallel to the line and there's no easy way of knowing if it was setup correctly after the face. Wouldn't it be better to set up multiple high speed cameras at different angles

Doxin 5y ago
High speed cameras produce significantly more output data, which makes them more expensive I'd have to imagine. Not to mention a high speed camera misaligned on the finish is going to produce similarly skewed results. Anything not happening exactly along the optical axis is getting distorted by perspective. At least a line camera doesn't pretend to have accurate information on anything except the line you aim it at.