The Nascar Camera Tech Behind a Historic 0.001s Photo Finish

Well, camera placement matters in the obvious way: it has to be on the finish "line". Where "line" is really a plane extending vertically from the line drawn on the surface.

I vaguely remember an article about a bike race photo finish that showed that this is not a given and reverse engineered where the camera was pointing (based on background) and who the likely winner was.

edit: found it https://www.tglyn.ch/blog/amstel_gold/

> a foot is roughly equal to a nanosecond

I used to work with a company who insisted on timestamping their sensor data with nanosecond accuracy. Mind you they were not working on anything high speed, or explosive in nature. Just robots moving around at best with highway speeds.

I asked them if they care so much about the accuracy will they also adjust their data for time-of-flight delays. Since by the time the light bouncing from an object hits your lidar/camera meters away what you are sensing is several nanoseconds the past.

To top it off they stored the nanoseconds elapsed since the unix epoch as a float double. So floating point weirdness immediately destroyed all the precision they worked so hard on.

I do appreciate that lightspeed is "about a billion feet per second" and it's also a number that's known exactly, since the foot is defined in terms of the speed of light in a vacuum.

As Grace Hopper so elegantly pointed out. She gave me one of her many nanoseconds, which were lengths of scrap telephone wire cut to a little under a foot long.

https://americanhistory.si.edu/collections/nmah_692464

This is brilliant, thanks for posting. Things like this make me miss my deceased father. I would love to discuss this with him. He was the only person I knew of that genuinely loved thoroughbred horse racing for the beauty of the animals and for the sport. We would camp out right on the finish line at Belmont park (and often on random weekends when the place was mostly empty) and stay put for hours waiting for the Belmont Stakes. He was an amateur photographer and once got a press pass to photograph from the trench along the outside of the track. I noticed the tall narrow mirror mounted to the finish line pole, and he said it was for the photo finish camera but, not much elaboration beyond that.

Another interesting takeaway is that because you are taking a single line capture the pixel distance equates to time not to distance like a normal image.

What that means is that if you pick two points on the car, you can measure that distance in pixels and multiply by the frequency to get change in time. Divide the actual physical distance of those two points by that result and you know how fast the car was traveling.

That’s mitigated a bit by the airflow implications of longer splitters, where a few extra cm might cost you more in drag or downforce reduction than you’d gain in a photo finish like this.

Would be difficult to use the hood. The front edge of it sits farther back than the front of the car and the seam could be difficult to find.

I don't think the teams are allowed to change the splitter size.

My beef is that NASCAR uses a rolling start. This isn't a horse race or Olympic 50m dash where all racers start in the same place under a starters pistol.

Buescher started 4 rows behind Larson. Doesn't that mean he raced the 400 miles faster than Larson?

Splitter length is very strictly regulated, as is every part of the stock car. There have been big penalties for much more subtle infractions, especially in the last few seasons with the current car design.

> You would expect teams to game the system and use longer splitters if photo finishes happen often enough. Tried taking a look at the regulations and it seems that they're not publicly available.

NASCAR cars are standardized and measured before and after every race. Failing a race inspection severely penalizes the team (loss of points, driver or crew chief suspensions, fines). Failing a pre-race inspection means the car doesn't race until it passes inspection. Teams aren't allowed to install splitters with different lengths than their competitors.

NASCAR, however, will mandate different splitter measurements for different racetracks. Still, all cars at each racetrack must use splitters that match NASCAR's requirements.

NASCAR fan here. Over the years the measurements of the car have gone from metal templates laying over the car to using lasers, with 1/32 of an inch making a difference.