3 ms·
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
by gorgoiler 6y 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 6y agoAh 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 In another comment I was discussing the tech being somewhat outdated - perhaps your suggestion is part of the solution.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 6y agoIt’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.
- dmurray 6y ago> Would two cameras on different planes result in more accurate results? A man with one watch knows what time it is. A man with two is never sure.
- reedf1 6y agoDoesn't the difficulty here become the limitations of the sensor? And perhaps lens distortion?
- falcolas 6y agoIt's my understanding (and confirmed by other comments on HN to this article) that the rules define the camera's sensing plane as the finish plane. So, regardless of the paint on the ground (which can not and will not ever form a perfect line), it's the camera that matters.