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Maybe ten years ago, I read a blog post by, I think, a French company called snips, that explained how their app used the pressure sensor to detect when the tra
by rossant 2y ago
Maybe ten years ago, I read a blog post by, I think, a French company called snips, that explained how their app used the pressure sensor to detect when the train entered or leaved a station. It turned out there was a very clear signal due to the sudden pressure increase or decrease when the train entered or left the tunnel between the stations.
Edit: found it. https://medium.com/snips-ai/underground-location-tracking-3ea56803dddc https://medium.com/snips-ai/underground-location-tracking-3e...
- panick21_ 2y agoThe Berlin Airport was ventilated by the train. But because the building was finished but not operational, for almost a decade the local train company had to drive trains in and out of the building.
- LukaszWiktor 2y agoVery few Android phones have a pressure sensor.
- maven29 2y agoJust like the heart rate monitor, this was also moved into smartwatches for optimizing revenue from those who truly need it.
- resoluteteeth 2y agoAre you saying that smartphones used to have heart rate monitors but they were removed to force people to buy smart watches?
- astrange 2y agoAny phone that can record 120fps video has a heart rate monitor, if you can calibrate it.
- connicpu 2y agoI forget which generation it was now, but many years ago I had a Samsung Galaxy phone that had a sensor that could measure your heart rate if you put your finger over it
- superhuzza 2y agoThe Galaxy S7 definitely had this feature. The problem is, it was basically useless. The main use case for heart rate monitoring is continuously throughout the day/night, or during exercise. A watch is very good at this. An optical sensor on the back of your phone is not. Periodically checking your heart rate by holding your phone in a specific way is not a useful feature for that many people.
- 6510 2y agoFor me, just having something that you can check 1 time per year is much better than nothing. The anecdote: I was working two heavy manual labor jobs 7 days per week and felt absolutely fantastic, glowing with power. Turned out the heart rate at rest was 180 lmao. Like a rabbit. Took a few days off, it dropped below 70.
- idiot900 2y agoIf your heart rate at rest is truly 180, you have an arrhythmia and need to see a doctor.
- 6510 2y agoIt should decline some 60 sec after physical activity. I think I measured after 10-15 minutes. Fatigue, dehydration, lack of sleep, a diet with lots of coffee. I just added those to the todo list. I went home to sleep (and confiscated the heart rate meter), the next morning it was around 100 bpm which is still terrible shape. Over the day it sunk to 80, over the 2nd day to 70, 3rd a bit lower. Back at work it would barely elevate. The moral of the story: Don't work out 11 hours per day for 6 months straight.
- 2y ago
- varelse 2y agoThe heart rate monitors in Google and Fitbit devices are insanely inaccurate during exercise. I had suspected as much already. Whenever a brisk walk indicated my pulse was 150 or so. But first, I could not reproduce this wearing a halter device and later I could not reproduce this wearing a polar heart rate monitor or a Frontier X2 ECG. Conclusion, Fitbit and Google heart rate monitors on those wearables are hot garbage. Cue some snooty googler insisting I'm doing it wrong somehow.
- rossant 2y agoMaybe premium Android smartphones do? My Galaxy S24+ seems to have one. Edit: at least the excellent Physics Toolbox Sensor Suite gives me a barometer signal indicating 102570 Pa right now.
- LukaszWiktor 2y agoTrue. Flagship smartphones, and some rugged models do have a pressure sensor.
- sliken 2y agoI was pleasantly surprised to note my pixel 9 has a barometer, 81,500 or so right now, I'm at 6,000 feet of elevation.
- plantain 2y agoVery many do - https://m.gsmarena.com/results.php3?chkBarometer=selected https://m.gsmarena.com/results.php3?chkBarometer=selected
- LukaszWiktor 2y ago> Your search returned 653 results. When you remove the filter, it returns 12177 results. So only ~5% of phone models include a barometer.
- yccs27 2y agoThat's all phones ever, not current/popular models. When you restrict it to the last 10 years, you get about 12%, and of the 70 most popular models almost a quarter are equipped with a barometer.
- antonkochubey 2y agoHuh? I restricted it to 2023-now, and got 146 results. 80 for 2024 only.
- lolinder 2y ago
- fragmede 2y agoyou wouldn't need all of them to have it, just enough so that wifi beacons in-between train stations could get added to the bssid - gps coordinate map. Though if the vendors wanted work with you, you could just tell them wifi bssid and the gps coordinates of them and the rest of it would just work.
- Normal_gaussian 2y agoThere are unlikely to be wifi basestations detectable in between stations, because these are underground trains.
- fragmede 2y agounless installed by the system operator, which is why they'd know the gps coordinates for them I'd have to have missed the title of the post, not read the post itself, not read GP's comment, not thought about why there'd be a pressure change, to have missed that particular detail. I appreciate you trying to be helpful though. :)
- _kb 2y agoYou don’t need fixed base stations. Just infra on the train that rolls bassid based on location data the train already has. This would silently hook into native location services already on devices without additional sensing or models trained on other sensor data.
- ssl-3 2y agoThat's... actually pretty brilliant. I wonder if it'll Just Work [eventually, given enough repetitions], or if the crowd-sourced network location algorithms will filter it because it is dynamic.
- bluGill 2y agoThere should be - everyone on the train wants connectivity. Even if there is wifi on the train, that wifi needs something to connect to.
- oniony 2y agoI believe many do because it's used to fix GPS data when at different elevations, if I remember correctly. https://nextnav.com/why-phones-have-barometers/ https://nextnav.com/why-phones-have-barometers/
- telgareith 2y agoMaybe it'll help achieve a lock faster- but theres nothing else needed for GPS besides GPS. The military really doesn't like dependencies.
- traverseda 2y agoNot a faster lock, air pressure is actually more accurate on the z axis for the most part. GPS is not great at height, and including an extremely accurate barometer is a big help.
- umeshunni 2y agoWhy is GPS not great at height? If you know your location is x,y and you have an elevation map, you can map x,y to an altitude z, right?
- Wowfunhappy 2y agoI know nothing about this, but I imagine two people at the same latitude and longitude could be at different altitudes. A trivial example would be people on different floors of a skyscraper—although I suppose gps works poorly indoors anyway. Still, even outdoors there are peaks and crevices, and on a steep slope a very trivial change in lat/lon could lead to a major change in altitude.
- ScottEvtuch 2y agoI would imagine it's because your distance to the satellites changes more when you move along the ground than when you move up and down the same amount.
- adastra22 2y agoI’m pretty sure every Android phone does. It’s called a microphone. It doesn’t give absolute pressure values, but that is not needed for this use case.
- coumbaya 2y agoAnother tidbit: on high speed trains (maybe on regular trains too idk) the 'door flange' which is actually a hollow pneumatic tube (it can detect spike in pressure that's how the train know it's trying to close the door on somebody's hand) get's pressurized higher before entering the tunnel, to mitigate the "slam" effect due to the difference in pressure.
- the-rc 2y agoEven before that, there was a Google Maps experiment using the compass (magnetometer) to infer train movement, but IIRC the accuracy of that depended on the network's current (DC vs AC) and even the vintage of the cars.
- mapt 2y agoThing about training sensor fusion algorithms - more sensors, more better. Often adding a terribly inaccurate sensor whose failures are uncorrelated with the ones you're currently using, because it operates on an unrelated principle, is the thing that makes the solution highly accurate.
- 30blay 2y agoHi! Having worked on this project, I can provide some details on why we didn't end up using the pressure sensor. As others have stated, not all phones have pressure sensors, and the quality of the readings also varies a lot between different models. For example, we had one device where the readings would spike when squeezing the phone. Transit also doesn't have permission to read the pressure sensor, and our use case wouldn't justify asking for it.
- WhyNotHugo 2y agoHave you considered publishing the data gathered and/or the generated models? For others wanting to implement similar functionality, it would be great if they didn't need to re-do the entire work from scratch.
- cosmojg 2y agoEh, I wouldn't count on it. Transit's trying to compete with the behemoths, and this seems to be their latest shot at securing a competitive advantage. I, too, hope they open-source their work eventually, but I also want to see them succeed in disrupting the transportation navigation space! (Not that those things are mutually exclusive, of course.)