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

504 点作者 tomglynch大约 4 年前

28 条评论

mvanaltvorst大约 4 年前
Is it just me, or is it really obvious that Wout won?<p><a href="https:&#x2F;&#x2F;i.imgur.com&#x2F;g78YNla.png" rel="nofollow">https:&#x2F;&#x2F;i.imgur.com&#x2F;g78YNla.png</a><p>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).<p>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&#x27;s wheel was ahead. Including the exact period where Wout passed the actual finish line.<p>If Tom would have passed Wout, you would expect that the bottom wheel would be more &quot;squeezed&quot; such that the end of Tom&#x27;s wheel would have passed the camera line earlier than Wout. Same for the other landmark (centre of wheel).<p>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.<p>Amstel gold made the good call, though I agree that it was probably more luck.
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nsteel大约 4 年前
There&#x27;s a arguably better, higher level writeup at <a href="https:&#x2F;&#x2F;cyclingtips.com&#x2F;2021&#x2F;04&#x2F;making-sense-of-the-controversial-photo-finish-at-amstel-gold&#x2F;" rel="nofollow">https:&#x2F;&#x2F;cyclingtips.com&#x2F;2021&#x2F;04&#x2F;making-sense-of-the-controve...</a> which concludes:<p>&gt; 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.<p>&gt; According to UCI regulations, the photo finish verdict is final, because the finish line is what the photo finish says it is.<p>Which makes most of the detective work here sadly pointless.<p>Pidcock probably didn&#x27;t need to tweet his take, in the same way he didn&#x27;t need to post that ridiculous bogus 5k time! <a href="https:&#x2F;&#x2F;www.rouleur.cc&#x2F;blogs&#x2F;the-rouleur-journal&#x2F;the-column-tom-pidcock-5k-time-proves-he-ll-win-the-tour-de-france" rel="nofollow">https:&#x2F;&#x2F;www.rouleur.cc&#x2F;blogs&#x2F;the-rouleur-journal&#x2F;the-column-...</a>
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gorgoiler大约 4 年前
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.<p>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.<p>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.<p>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.<p>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 <i>arbitrarily</i> angle the camera plane to intersect the finish plane.<p>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.<p>I think the article assumes the former when the organisers did the latter?
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fotta大约 4 年前
I used to work with these line-scan photo finish camera systems (we used FinishLynx) timing track meets.<p>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&#x27;s pretty clear it wasn&#x27;t aligned properly. The cameras can auto-align, but we didn&#x27;t trust it and manually aligned it, but I&#x27;m wondering if maybe the event organizers auto-aligned and didn&#x27;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).<p>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&#x27;ve been a tough background color. Also a black line is questionable. I would&#x27;ve had a white line on black base for the same reasons.<p>[0] <a href="https:&#x2F;&#x2F;www.finishlynx.com&#x2F;product&#x2F;accessories&#x2F;camera-mountings&#x2F;remote-camera-positioner&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.finishlynx.com&#x2F;product&#x2F;accessories&#x2F;camera-mounti...</a>
toast0大约 4 年前
Some thoughts from looking at amstel_Finishphoto_AGR21.png.<p>a) in the horizontal axis, everything changes at 6 pixel intervals, I&#x27;m going to call those samples<p>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).<p>c) there&#x27;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)<p>d) there&#x27;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)<p>I&#x27;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&#x27;m comfyish saying the bottom rider was 2 samples behind the top at the finish line.<p>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&#x27;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.<p>also e) now I&#x27;ve used up my evening time I had meant to do something else with :P
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MR4D大约 4 年前
Fascinating article, and great to see a problem solver at work.<p>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).<p>At what point do races become a tie instead of 1st&#x2F;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?<p>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: <a href="https:&#x2F;&#x2F;www.theringer.com&#x2F;2020&#x2F;7&#x2F;29&#x2F;21345181&#x2F;milorad-cavic-michael-phelps-2008-olympics-beijing-100-butterfly-conspiracy" rel="nofollow">https:&#x2F;&#x2F;www.theringer.com&#x2F;2020&#x2F;7&#x2F;29&#x2F;21345181&#x2F;milorad-cavic-m...</a><p>This article seems to make the argument quite well: <a href="https:&#x2F;&#x2F;olympics.time.com&#x2F;2012&#x2F;07&#x2F;27&#x2F;technologys-touch-how-a-photo-finish-in-the-olympic-pool-gets-resolved&#x2F;" rel="nofollow">https:&#x2F;&#x2F;olympics.time.com&#x2F;2012&#x2F;07&#x2F;27&#x2F;technologys-touch-how-a...</a>
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tomglynch大约 4 年前
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: <a href="http:&#x2F;&#x2F;tglyn.ch&#x2F;blog&#x2F;images&#x2F;amstel_Finishphoto_AGR21.png" rel="nofollow">http:&#x2F;&#x2F;tglyn.ch&#x2F;blog&#x2F;images&#x2F;amstel_Finishphoto_AGR21.png</a><p>The curve of the spokes should mean we can determine the distance the rider has traveled after the photo-finish camera.<p>I cover my other ideas in the &#x27;Further research required section&#x27; about 75% of the way down the article. If you have any further suggestions please let me know. Tom
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FearNotDaniel大约 4 年前
As a child I was taught that sport should be &quot;sportsmanlike&quot;. Perhaps in a situation like this, the real solution should be &quot;I say, it&#x27;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&#x27;s all go to the pub and celebrate.&quot;
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mhandley大约 4 年前
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&#x27;t know how they set up these cameras to ensure they&#x27;re parallel with the line, but this seems at least as likely as aligning the camera parallel but in the wrong place. I&#x27;m not sure how you&#x27;d be able to tell from the images though, but it would make a much bigger difference to the actual result.
jrnvs大约 4 年前
Here&#x27;s an interview with the photo operator, in Dutch: <a href="https:&#x2F;&#x2F;nos.nl&#x2F;artikel&#x2F;2377417-fotofinish-operator-amstel-gold-race-twijfelt-niet-je-ziet-dat-pidcock-te-laat-is" rel="nofollow">https:&#x2F;&#x2F;nos.nl&#x2F;artikel&#x2F;2377417-fotofinish-operator-amstel-go...</a><p>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&#x27;s all been set up correctly.
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runningmike大约 4 年前
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.
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deanpea大约 4 年前
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?
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tgtweak大约 4 年前
Taking &quot;Internet Detective&quot; to new and exotic levels.
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abel_大约 4 年前
I think the distortion of the video-finish camera should be considered when making these estimates. There&#x27;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.<p>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).
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cycomanic大约 4 年前
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&#x27;t think this is necessarily the case. It depends on the height of the camera, the angle and possible distortions.
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getlawgdon大约 4 年前
I&#x27;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&#x27;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.
PaulHoule大约 4 年前
I&#x27;ve wondered what you&#x27;d get if you put a &quot;photo finish&quot; 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.
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xmprt大约 4 年前
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.
ernesth大约 4 年前
I assume the finish line should correspond to the scaffolding above the road that sports &quot;Finish&quot;. <a href="https:&#x2F;&#x2F;www.tglyn.ch&#x2F;blog&#x2F;images&#x2F;amstel_photofinish_camera_position.png" rel="nofollow">https:&#x2F;&#x2F;www.tglyn.ch&#x2F;blog&#x2F;images&#x2F;amstel_photofinish_camera_p...</a><p>The computation by the author of the article indeed confirms this: <a href="https:&#x2F;&#x2F;www.tglyn.ch&#x2F;blog&#x2F;images&#x2F;amstel_approx_line.png" rel="nofollow">https:&#x2F;&#x2F;www.tglyn.ch&#x2F;blog&#x2F;images&#x2F;amstel_approx_line.png</a><p>My point is that it is the painted line that was not correctly placed rather than the camera.
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jrudolph大约 4 年前
Awesome research. I have similar quibbles about photo finish cameras in sports and written about them [0].<p>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.<p>[0] <a href="https:&#x2F;&#x2F;www.rowinginmotion.com&#x2F;thoughts-fairness-rowing&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.rowinginmotion.com&#x2F;thoughts-fairness-rowing&#x2F;</a>
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xpe大约 4 年前
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.<p>Wout!!!<p>&gt; According to UCI regulations, the photo finish verdict is final, because the finish line is what the photo finish says it is.<p><a href="https:&#x2F;&#x2F;cyclingtips.com&#x2F;2021&#x2F;04&#x2F;making-sense-of-the-controversial-photo-finish-at-amstel-gold&#x2F;" rel="nofollow">https:&#x2F;&#x2F;cyclingtips.com&#x2F;2021&#x2F;04&#x2F;making-sense-of-the-controve...</a>
sachkris大约 4 年前
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?
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Havoc大约 4 年前
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
Rastonbury大约 4 年前
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&#x27;s no easy way of knowing if it was setup correctly after the face.<p>Wouldn&#x27;t it be better to set up multiple high speed cameras at different angles
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scotty79大约 4 年前
Or you could just change the rules and declare that the finish line is wherever the camera is pointed at and what&#x27;s painted on the ground is just a rough indicator of where the finish line actually is.<p>Or maybe rules are already exactly that?
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tsjq大约 4 年前
Too much work, IMO. Just give them both Gold medals.
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dekhn大约 4 年前
Time differences like this are insignificant.
helsinkiandrew大约 4 年前
I&#x27;d say that was a draw.