That'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.
For an app as popular as Transit this is a purely academic exercise—25% of the most popular models is way too low to be worth building their detection around, even if they could assume that all of their customers use the most popular models (which they obviously can't).
25% of popular models doesn't mean 25% of phones currently in circulation. If the iPhone has a barometer (which it does), that's already a huge share of phones out there.
It may be too low, but I'd imagine the app could also look for other Transit users nearby and as long as one of them has the appropriate sensor, this might be sufficient. Probably still not something you want to rely on since it would be pretty annoying to have a feature not work when you're alone on a train.
> the app could also look for other Transit users nearby
That seems unlikely in an environment with no cellular / wifi signal. Theoretically possible, but expensive for battery and probably disallowed by the OS.
Does the current version of their app run on 25% of the most popular models? This update runs a classifier on your phone. I imagine that would be no less restrictive than the barometer requirement.
Most classifiers are nowhere near as heavy as the LLMs that are trending right now. The article doesn't specify, but I would be surprised if the resource requirements are especially onerous.
Inexpensive barometric sensors are _remarkably_ sensitive too. Like enough precision to detect less than 10cm or 4" changes in height/altitude.
Note that's "sensitive", not "precise". The atmosphere changes pressure with the weather, so you don't get accurate absolute altitude - at least not without knowing the local "pressure altitude". Barometric pressure can vary in a way that represents plus or minus 300 or 400m of altitude, and can swing between high and low fairly rapidly in extreme weather events.
But over short timeframe the change in barometric altitude can be very useful. Glider pilots (including paragliders and even RC gliders) often use very sensitive barometric pressure sensors to detect when they're in rising to sinking air, down at the few meters per minute range of sensitivity.
Not 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.
Because the SATs only give you a pseudorange distance between you and the sat, so each say is most accurate solving for distance to/from that sat, and much less helpful resolving angle to the sat.
With a clear SkyView, around just under half of the sats are hidden by the earth.
This means that you get a full 360 degrees of data that can be near the horizon helping resolve lat/long.
But only about half of that sky is helpful for altitude. The birds you can't hear directly below the earth would be the most helpful for improving the altitude fix if you could hear them.
Baro is handy because you can take the absolute altitude from GPS as a low frequency baseline and use the baro for high frequency changes. Then when GPS says we teleported +200 feet when a new sat comes into view, we can temper that that with baro information.
I 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.
I 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.
Sure, assuming you are not in a building, balloon, helicopter, plane, drone, etc. Not to mention interesting topology like a cliff where an error in long/last of even a single foot could mean your altitude would vary by 1000 feet.
One problem is that using position to get altitude would require a detailed elevation map and that would use a lot of storage space or require internet.
But elevation maps are not detailed enough and position is not accurate enough to get accurate elevation. Think about standing on trail along steep slope. The position not being that accurate is fine since you know you are on trail. But altitude could vary wildly going up or down slope, or even up or down trail. It is probably similar to GPS vertical accuracy, but were going for more accuracy that barometer provides.
The maps are only used when resolving a 3 bird fix. As soon as you lock a fourth bird you can solve 3D directly rather than leveraging an onboard spheroid. Many receivers refer to a three bird fix as a 2D fix for that reason.
It's one factor in estimating altitude you feed into an extended kalman filter. If the GPS altitude is holding steady but there's a sudden jump in pressure that's probably a storm front not indicative of motion.
you 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.
You 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.
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.
unless 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. :)
I’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.
I 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
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.
+1. If a phone has a stopwatch, you can get your bpm at a given moment with a finger and a multiplication (or patience). Given the limited real estate on a mobile phone it's crazy to devote any space for something so trivial.
For 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.
It 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.
The 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.
