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No GPS required: our app can now locate underground trains
- mdergosits 2y agoSome cities will put BLE beacons in tunnels that transmit the location and then you can find your location via the strongest beacon signal. This seems like a nice way to figure that out without installing hardware!
- IshKebab 2y agoSome trains even have modern technology called "screens" that display their current location, next stop, route and so on! (Although in fairness they so often get this laughably wrong, and cycle through useless "remember your luggage" style messages so you have to wait like 20s to see the information you want - critically bad on a train.)
- the_mitsuhiko 2y agoI really don’t understand why not every subway shows the next station on the screen instead of warning messages and other stuff. (And a marker for side the doors will open)
- dietr1ch 2y agoI don't get why ads are prioritised over travel information.
- eythian 2y agoFor at least months in my city, the screens in buses have been showing a "broken image" icon as part of their ad cycle. I'd much rather know about the next stop.
- kdmccormick 2y agoIt's very simple: Transit in many places is underfunded. Travel info screens cost money to install and maintain. Ads, on the other hand, make money.
- bluGill 2y agoAds make money, but not that much. I'm not convinced they are enough to be worth the bother. To have ads you need to pay people in sales to sell them, people to install them (now that this is electronic it is easier than the old paper days, but you need a more expensive tech person to keep them working). At best they are 5% of your gross budget, so not very significant and they often hard harmful to your riders.
- rtkwe 2y agoTransit in the US seems to be constantly on a starvation diet budgetarily speaking so I'm not shocked small sums of money get chosen over options that would be better for their users.
- rangestransform 2y agoStarvation diet? You should see how much NYC MTA spends, it’s a feast compared to even the rest of the anglosphere
- rtkwe 2y agoThe MTA is a huge outlier but still gets less money for upgrades and upkeep than they need. They limped along for years on extremely outdated train tracking infrastructure and are just getting around to doing updates that needed to be started two decades ago.
- rangestransform 2y agoThey get way more than they need, it’s just burnt on unions, pensions, and consultants I will literally volunteer my time to canvass for anyone who runs on busting NYC public sector unions
- faggotbreath 2y ago[dead]
- IshKebab 2y agoI assume it's because the person deciding what goes on the screens is some manager somewhere. They probably just don't really thing about it.
- IncreasePosts 2y agoAlso doesn't help travelers who aren't too familiar with English - I always wonder how many NY-bound tourists have stepped off the train at "Newark Penn Station".
- SoftTalker 2y agoEven better, they have a thing called a "window" which is transparent and you can look out on the platform and see the sign posting the station name.
- brewdad 2y agoThis assumes you aren’t riding a packed train with people standing wall to wall in front of seated passengers. Being a shorter than average person also can make this a challenge.
- spaceywilly 2y agoI take the train every day in NYC. Around half the time the train is brand new and has nice displays that even show you where the stairs are located in each station as you pull up. The other half the train is from the 1960s and has no information whatsoever. So yeah this app will definitely be an upgrade over peering out the window to read the station names. Even the trains with displays are occasionally wrong/not working.
- fennecbutt 2y agoLondon tube is slowly getting mobile signal on lines, but every platform has station WiFi so it'd definitely be possible just to use that.
- scottbez1 2y agoThis is super cool! As a regular BART commuter I always thought it'd be fun to try and build a location classifier based on the screeches in different tunnel locations, but using accelerometer data is probably much more practical.
- sitkack 2y agoTune the screeches so they make a different chord for each stop.
- Lance_ET_Compte 2y agoI have no hearing in any of the frequencies BART trains emit. Burned away... I do love this "Transit" app though.
- sitkack 2y agoI am sorry for your loss, but does this explain dubstep?
- ant6n 2y agoUsing the microphone as a sensor is a bit of a no-go a transit app. You could just record the noise of the train rolling to find out the movement, but your users will suspect you are listening to them.
- isaacfrond 2y agoAnybody know what model architectures they used? The motion detection might be a convolutional network or an svm. The mixer model perhaps a classic neural network.
- iAkashPaul 2y agoCould be that or an RNN/LSTM as well
- mjamesaustin 2y agoThis is one of the best apps I've ever used, and I'm excited to see it's only getting better!
- fullofstack 2y agoIs GPS spoofing an option, underground? Would instantly work on all phones.
- dietr1ch 2y agoIs it spoofing if you are telling the truth? Just pretend to be a GPS satellite during its morning commute.
- szszrk 2y agoWell, you are not a GPS satellite, so you are indeed spoofing military equipment. On a serious note, I recall that smartphone location in metro in my city started to "just work" as soon as all stations and tunnels had indoor cell towers. Suddenly all apps worked fine and I forgot that problem ever existed. Modern location detection is as scary as it is amazing.
- bluGill 2y agoCell towers also transmit location data
- _flux 2y agoYou'd need to spoof at least three satellites to get a fix, right? And then you'd need to spoof different signals for different regions of the subway, because your signal sources aren't really in the orbit. Sounds to me this could be very complicated and expensive. I wonder if it would even be possible because you'd need to have the same signal spoof the correct positions to everyone who hears that signal.
- dietr1ch 2y agoNo, you need 3 satellites because they are far enough that their position and time gives you too much uncertainty. If the entire sphere where I could be fits within 5m I guess I don't need other satellites and their time to start intersecting spheres.
- dietr1ch 2y agoThis is really cool. Sort of related, what I find kind of silly, is that my car probably knows really well where I am, but can't help my phone figure out where my car is pointing to despite being connected to it.
- MaxikCZ 2y agoThats still surprisingly unsolved problem. I was daydreaming about pulling my laptop out somewhere without known wifi and it automatically using my phone as a hotspot, without going trough manual process of enabling said hotspot. Somehow we connected the world but forgot to connect out devices..
- vineyardmike 2y agoThis has almost been a feature for Macs+iPhones for like a decade. You need to manually "pick a wifi network" but it'll turn on your phone's hotspot if you pick it from the list.
- pjerem 2y agoNever tried on my Mac, but on iPad, it’s totally automatic : the iPad automatically tells the iPhone to enable the hotspot (over Bluetooth I presume) then connects to it.
- wisenull 2y agoIs the hotspot truly off? I am asking because it was really common to see Whoever's iPhone whenever you were picking a wifi network.
- astrange 2y agoThe hotspot uses a lot of power, so it really is off when it's not being used.
- klausa 2y agoMy understanding of CarPlay is that it does offload GPS to the car (when available, not all units/manufacturers might support it).
- __MatrixMan__ 2y agoOh thank goodness. I knew I buried a train somewhere around here but I just can't find it.
- aziaziazi 2y agoLets be the bad guy today: https://news.ycombinator.com/item?id=7695956 https://news.ycombinator.com/item?id=7695956
- ThePowerOfFuet 2y agoThat says "Please don't post substanceless one-liners here." The joke was _two_ sentences, and I, for one, appreciated it. If you're going to quote regulations, make sure to bring a gun to a gun fight!
- aziaziazi 2y agoWell I think "one-liner" here adds more weight to "substanceless" and was not indented to be taken literally: - it has no useful meaning in a media you can resize. - adding dots (.) does not noticeably change the meaning, you could replace with a comma : "Oh thanks goodness, I new…", allowing cheating on the fight rules. I don’t think that’s desirable way we want to interact as a HN-user-community (personal opinion) - taking the literal read anyway, I see one line and two sentences right now. It’s a one liner. (not English native, may I missed a secondary meaning?) Dang clarify it bellow the post in linked and cite scott_s, none of which talking about the length of the joke but both referring to noise. I personally also found it funny BUT I also saw like 10 substanceless not-so-funny jokes today on HN. INHM problem is not the joke itself but the emptiness of the post if you take the joke aside.
- maronato 2y agoWell, seeing as GP is still visible 20h later, I’d say not enough people share this view. Which is good, IMO, since one important property of a social system is flexibility.
- aeternum 2y agoWhy does the acceleration graph not take direction into account? Seems like you could get much cleaner data if you looked only at the directions orthogonal to gravity.
- kaonwarb 2y agoThey're using Fourier transforms to focus on frequencies of acceleration associated with subway travel; gravity should mostly fall out as an independent factor.
- nickmooney 2y agoIs there always a great reference for which way down is, given that the phone can be in various orientations? You might have to do some other heuristics / build some other model for that to figure out which axis to subtract your 9.8 m/s^2 from - maybe it's easier not to worry about it.
- zokier 2y agoIsn't merging gyro data with accelerometer data pretty standard approach?
- nickmooney 2y agoI forgot phones have gyroscopes :)
- grav 2y agoVery impressive. Also interesting that the motion type prediction ("is this a moving train?") generalizes to underground trains in other cities. I see they support the the largest cities in Sweden and Norway, wonder if there are any plans for Copenhagen, Denmark?
- dotcoma 2y agoLet them know you’d like CPH ! Especially if you know someone at the transit agency or can help them even in a very small way.
- O-stevns 2y agoWhile I understand your question is about the Transit app in general, I'd just like to mention in correlation to the article that my team and I worked with one of the public transport operators in Denmark, to utilize the motion predictability feature found in Android and iOS SDK's, so I can enlighten you with some details regarding that. Our conclusion was that the feature didn't work in the danish metros for reasons we never got to deep dive into. It's most likely related to the fact that many of the metro stations are built in concrete, as such there's no GPS data in most of them unless you're very close to or on the surface and no motion data. I'd be surprised if they got this particular feature working but who knows... maybe if we had looked into the raw sensor output we might have been able to work something out. In the end we made a solution to help determine when you're moving or not by utilizing beacons.
- grav 2y ago> no motion data How come there's no motion data?
- modeless 2y agoSeems like you could do a better job of tracking progress between stations by detecting the specific acceleration signature of each segment of track. At least for tracks that are not completely straight and level. Somewhat similar to the first primitive in-car navigation systems before GPS, that worked on dead reckoning with drift correction by matching the shape of the measured path to map data.
- fire_lake 2y agoShazam for train tracks
- modeless 2y agoNow accepting funding offers at $10m post-money valuation cap
- blitzar 2y agoAi Powered Shazam for train tracks. Now accepting funding offers at $500m post-money valuation cap.
- rvnx 2y agoThen in 5 years: "Turns out this was marketing for investors and that our classifier was using 99% of the time last location and itinerary as primary factor to determine location" The magic formula: "if is_train_moving, countdown to next station"
- nuccy 2y agoAcceleration signature depends on: - human driver - train capacity and current load - train model (or any powertrain variations) More reliable might be to check rail track features from accelerometer: tilt, turns, bumps, or a combinations of everything. Even sounds on turns, changes of backround during merging tunnels, etc. Integrated acceleration gives train speed, which is also useful along with other inputs.
- eps 2y agoThere are metro systems where trains sometimes stop in the tunnels or go at slower speeds. I'm guessing this app won't work that well there. In fact it would probably generate false positives when labeling stations... ?
- wffurr 2y agoI was just wondering how well this would do on a system in poor repair with mixed generation trains that stop mid tunnel, i.e. Boston.
- DrNosferatu 2y agoNice! dead reckoning to another level (Y) ML level - for some reason, made me think of ITER / fusion research trying to predict plasma behavior with ML also. Any specific connections people in the know care to point out?
- daghamm 2y agoCorrect me if I am wrong, but this looks like something that Google would buy for 3.14B and quietly roll out to anything including your smart toaster. My point is, I see only one real business case for this.
- froddd 2y agoIt’s a strong business case for the founders
- araes 2y agoSimilar thought, and Google acquire does seem like a plausible route. However, checking over on Play [1] they've apparently got In-App purchasing at $3-50 and 300+ cities and 1000+ transits that let you buy fare and passes. Seems like they're already making money anyway. Teams pretty extensive though, so it does look like a lot of annual money's probably necessary to float. [2] [1] https://play.google.com/store/apps/details?id=com.thetransitapp.droid&referrer=utm_source%3Dtransit%26utm_medium%3Dwebsite-homepage%26utm_campaign%3Dwebsite-homepage&pli=1 https://play.google.com/store/apps/details?id=com.thetransit... [2] https://transitapp.com/team https://transitapp.com/team
- xav0989 2y agoThey also partner with transit agencies where the transit agencies pays them to upgrade everyone in the region/system to the premium offering, and the transit app becomes the official app for that transit agency.
- RobotToaster 2y agoYeah, I downloaded the app out of curiosity, but uninstalled it once I saw it had the usual freemium subscription nonsense.
- kccqzy 2y agoI never paid a single cent in this app and yet the app is perfectly enjoyable. I've used it since 2019. What's wrong with freemium? I don't need extra features and the free features are good enough for me.
- exabyte 2y agohttps://youtu.be/bFM9HHB9JXI https://youtu.be/bFM9HHB9JXI I found this to be a really well-done video on using quantum physics to track location integrating upon acceleration
- mattlondon 2y agoJust tried installing it on my commute in London. Didn't work - in fact it thought I was at the stop before the one I got on at (when I did have GPS) even when I was 5 or 6 stations further along on my journey. Then it spent the whole rest of the journey spamming me with notifications about the next departure time at the station I didn't get on at. Wildly inaccurate even with GPS it seems. Instant uninstall. Sorry.
- wtk 2y agoTheir website doesn't include London in the UK section (https://TRANSITAPP.COM/REGION https://TRANSITAPP.COM/REGION).
- andylynch 2y agoPretty sure that’s a mistake, they do elsewhere (https://transitapp.com/en/region/london/tfl https://transitapp.com/en/region/london/tfl ), and I’m using it ,right now. Not doing so would be astonishing given how many people use public transport here, and that TFL’s data is really, really open + easy to use.
- wtk 2y agoI checked twice in disbelief, but amongst many many places - London (UK) not being listed was surprising to me. I thought it's maybe some extra challenge of the oldest subway system.
- itsgrimetime 2y agoThat’s a bummer, I use it daily in SF and the tracker it has for upcoming buses/trains has always been super accurate, and the stop countdown is always dead on. It even tells me when I need to speed up my walking to make it to the next bus in case it’s running a little early.
- beejiu 2y agoCityMapper is probably the best app for London, although I can't recall how it behaves in deep tunnels. I think it may just use a timer to alert you when to get off.
- rossant 2y agoMaybe 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?
- voidUpdate 2y agoI'm still a little confused as to how this shows where a train actually is, it seems like this is only a solution to know when you're on a train or not. Does it just guess based on what trains should be moving at that time?
- rdsubhas 2y agoI'd assume it's the length (in time) of the vibration since the last stop. There may be edge cases where if the train is moving slowly, but overall it's a smart technique.
- voidUpdate 2y agoIf there's a delay that will really confuse it though, either if your train isn't going at the speed the app expects or it stops at a point outside of a station
- bluGill 2y agoIt probably would, but if someone has the app running, then the app knows what train they are trying to get on, and so if the data is all consistent with being on a train they are probably on that train. The app also knows where the train is, so it knows where you are as well. It won't know which train car you are on, but that normally doesn't matter. This probably is wrong if trains for both directions stop at the same time from opposite sides of the same platform and you get on the wrong train. However this is a rare enough case that we can ignore it - but very annoying if you are that person (this case happens to most transit riders once or twice in their life). Even when this happens there often is other location data scattered around so you would likely only ride a stop or two before the app realizes you are on the wrong train and can reroute you.
- svag 2y agoThis is a very interesting article. I suppose something similar can be made for vehicles entering a tunnel, where eventually will lose the GNSS signal. I have noticed that a year ago or so, Google Maps app would lose the GNSS signal and stop updating the position while there was no signal. But now I have noticed that the position is updated, although is not accurate. I wonder if something similar has been implemented...
- michaelt 2y ago15 years ago, sat nav systems built into cars would sometimes be fitted with a rate gyro and get a wheel speed signal from the car - to make them work better in tunnels and other areas with poor GPS signals. (Of course, that one area of superior performance couldn't make up for the awful GUIs, the awful resistive touchscreens, the $100 map updates, and suchlike)
- Cthulhu_ 2y agoI can't see inside Maps, but it does look like they use accellerometer data or just assumptions to continue animating your position on the map. Assumption being for example that you will follow the route through the tunnel at your current average speed. Close and good enough for most tunnels I suppose.
- sitkack 2y agoApple maps does this.
- maxehmookau 2y agoThis is so freaking cool. What a fantastic idea and a great write-up.
- h1fra 2y agoOh they so going to get bought by Google
- deleted 2y ago[deleted]
- tdiff 2y agoI believe Yandex does smth. similar in their navigation in Moscow, because GPS is heavily jammed in some areas.
- elromulous 2y agoCitymapper has been able to tell you what stop you're at for many years (at least on the NYC subway). How does their solution work?
- aitchnyu 2y agoTangential, why dont phones use accelerometer+gravity to figure out the path travelled and the "plane" its on when gps is out? Somehow my running app knows my stride length but may refuse to count the distance travelled when gps was out.
- killingtime74 2y ago(guessing) Stride length is a scalar, path is a vector? Inertial navigation systems suffer from a build up of the error. Perhaps it's not practical even if it's possible to calculate position based on those sensors alone
- sorenjan 2y agoTo get position from accelerometer data you have to integrate it twice. Accelerometer data is noisy, and integrating noise quickly leads to large deviations. That's why you need some kind of absolute position reference, like GPS, to not get bigger and bigger errors. Here, they seem to estimate which stations they are at or between, and use that as absolute references. Your running app is using accelerometer data to recognize when you're taking a step, and combining that with GPS data to measure how far you're running. So if it measures 100 meter using GPS and counts 100 steps during that time, your step length is 1 m. Garmin watches uses this to measure your running distance on treadmills, but they want you to calibrate it by running with GPS on a flat surface outdoor first. I don't know if any watches or apps use this in combination with GPS to make better position estimates when the GPS reception is poor, my guess is no because it's really only useful for distance, not position, and generally when running outdoors you're not running in completely straight lines. But it should be possible to estimate distance and combining it with their routing software to guess which way you took for short parts of the course.
- Woeps 2y agoUhm, Don't most underground trains already show you where you are? Or at worst, the sign of the station shows you your location?
- yaky 2y agoI think it's one of the "pointless but cool" projects, but yes, I don't get it either. Any decent underground system would already have audio and visual announcements; I don't think I have ever cared to know where between stations the train is.
- makeworld 2y agoSupporting it in the app allows connection info (bus, other train, etc) to be updated and to warn the user if they'll be late.
- aucisson_masque 2y agoSide note, that's why I don't like that the Google plays services in Android have a permanent access to Physical Activity that can't be disabled. Even without gps data, just having access to your phone accelerometer is enough to give a lot of data about your life. Cumulated with Google insanely big amount of data about wifi access point location, it means that they know where you are even without gps activated and how you got there.
- sourcepluck 2y agoAny good links for reading more about Play Services access to the phone's accelerometer?
- deleted 2y ago[deleted]
- alkonaut 2y agoI visited London this weekend and found even many underground _stations_ were without mobile service, 15 years after I got used to having spotless end-to-end mobile coverage even in deepest tunnels. I don't know why the London Underground lags that of other cities? Knowing the next station is usually a solved problem that doesn't need a smartphone, because that's displayed in the train itself and called out on speakers. But once you are on the platform and you need to ask the route planner what the fastest route is to a specific station (It could be walking to the surface and taking a bus, so it's not as simple as looking at the subway map) - then you are out of luck if platforms don't have 4/5G coverage!
- vinay427 2y agoThe usual answer that will be thrown around to justify this is that London has the oldest underground metro system, whether that’s relevant or not. It doesn’t seem very relevant when even the deepest stations in Prague (which are newer but much deeper than most of London) have later added 5G throughout tunnels with download speeds of ~200 Mbps between stations. I suspect the UK just doesn’t have modern standards for mobile internet service, as it isn’t limited to TfL services in London. There isn’t even reliable mobile coverage on stretches of the West Coast Main Line rail corridor in England, which is outdoors and connects the UK’s most populous cities. Much of London isn’t particularly reliable either on most mobile networks, in my experience. Meanwhile, in cities like Prague or Washington I can often get mobile download speeds outdoors of 400 Mbps - 1-2 Gbps.
- beejiu 2y agoAlmost all tunnel sections now have 4G/5G and everything should be done by the end of this year according to Tfl.
- lol768 2y agoThey've given "targets" and deadlines before and failed to meet them. I would take whatever they say with a large portion of salt.
- DrBazza 2y ago
- dmazin 2y agoThis is SO cool. I am actually currently working on a project to record the sound of the London Underground passing under me. We can very clearly hear the Northern Line under us. It's < 30 meters below us. I have become obsessed with getting high-quality, low frequency recordings of it passing under us. Why? I don't know. I just can't take my mind off it. For example, there are two tunnels (north and south bound). By correlating it with actual TfL data, can I figure out the sound signature of each? More intriguingly, I know that there are maintenance vehicles that operate under us in off hours. Can I "catch" them? I'm not sure what else I might do with this project, but the idea of capturing the sound of this semi-ephemeral creature that operates below me has captivated me.
- dmos62 2y agoThat's awesome. What sensors have you considered? I'm interested in extremely weak, high-frequency vibrations of everyday things while in resting state (which is sort of the opposite of what you're after, as I understand), but have not gotten far in acquiring the sensors. I'd love to get a laser doppler vibrometer, but they're pricey.
- dmazin 2y agoWell, I was just going to put a contact mic in my cellar. My understanding is that this is the best way to pick up low-frequency vibrations. I know very little about audio engineering. I wonder what else I might be able to use to pick up the vibration signature? I completely understand your drive to pick up those high-frequency vibrations! There's a whole secret world of vibrations out there, and we can analyze it!
- jbl0ndie 2y agoYou might struggle using microphones if it's very low frequency because most human audio microphones intentionally filter frequencies that are below (and above) human hearing range. Perhaps fixing to he contact mic to the right resonant object might serve to translate the low frequency to a higher frequency? Could you use the accelerometer on a smart phone to 'hear' the vibrations?
- snodnipper 2y agoI worked for signalbox.io and they had this for the London Underground ~8 years ago. There was some impressive maths / approaches behind all of the "magic".
- bambax 2y agoDead reckoning is... hard. https://en.wikipedia.org/wiki/Dead_reckoning https://en.wikipedia.org/wiki/Dead_reckoning The first car navigator, the Etak, came out in 1985 and used dead reckoning and quantization to tell where the car was on the map; see this excellent article from 2017: https://www.fastcompany.com/3047828/who-needs-gps-the-forgotten-story-of-etaks-amazing-1985-car-navigation-system https://www.fastcompany.com/3047828/who-needs-gps-the-forgot... Today dead reckoning is used in aerial navigation, and commercial planes (and others) are equipped with Inertial Navigation systems to supplement GPS information; they are getting more and more precise but can still go wrong and need frequent re-calibration. The next step is "Quantum Positioning System" that promises to detect infinitely small movements and produce perfect dead reckoning at all times, with a precision of the order of one centimeter. It has already been tested successfully. For now the machines are heavy and extremely expensive, but it's imaginable that in some not-so-distant future the technology will be much more available. https://newatlas.com/aircraft/quantum-navigation-infleqtion-test-flight/ https://newatlas.com/aircraft/quantum-navigation-infleqtion-...
- jackdh 2y agoThere is a very good set of podcasts[0] by Cautionary Tales about the German V2 rockets in WW2 which tried to use this. It was so hard the Allies allowed them to continue wasting money on it during the war. Well worth a listen to if you're into that. [0] https://timharford.com/2023/07/cautionary-tales-the-v2-trilogy/ https://timharford.com/2023/07/cautionary-tales-the-v2-trilo...
- zokier 2y agoGeneral dead reckoning is hard. But dead reckoning for train travel should be massively easier. Train movement is constrained to tracks so you only need to resolve how far along track train has moved + possible junctions, which should already make the problem much simpler than e.g. airplane ins where you are resolving full 3d position. To make things even more easier, you only need to reckon between individual stops which prevents error accumulation over the whole trip. Lastly you have schedule information, so you know roughly where the train should be at any given moment.
- DrBazza 2y agoIs this the same sort of technique that Shazam uses?
- barbegal 2y agoWith this sort of tech it only achieves good usability if it is accurate a high percentage of the time. Anything less than 90% accuracy on a whole trip and I likely won't trust it. So that means getting to >99% accurate on each underground train stop. I'm still not sure if this tech reaches that sort of threshold or if this is one of those things that looks like a good idea on paper but falls apart in real world use cases.
- sitkack 2y agoOnce enough people have the app, there will be a whole time varying point cloud of data both on and off the train.
- datameta 2y agoIs that their stated goal? Are they not saying they will not use user virbation data?
- sitkack 2y agoI'd assume they would have some opt in, or allowance for either federated learning or sharing of anonymized sensor data. Google is a huge advantage here, they have both the spatio-temporal intent of the user as well as the physical flow feed. There is so much position data flowing off android phones, that they are able to see the whole topology.
- wffurr 2y ago"Classifier" how quaint. I am impressed that they wrote the whole article without mentioning "AI" one time.
- worewood 2y agoGood. Shows that engineering is on the driver seat, not marketing.
- PittleyDunkin 2y ago[flagged]
- devit 2y agoWouldn't dead reckoning with the accelerometer and gyroscope in addition to their machine learning improve this significantly? (constraining motion along the known tunnel path when in a moving train, constraining the user to be within the train stopping rectangle when detecting a train starting to move) Or is the hardware in smartphones too inaccurate even with the extra information?
- pbmonster 2y ago> Wouldn't dead reckoning with the accelerometer and gyroscope in addition to their machine learning improve this significantly? The thing that should help the most would probably be the hall sensor/magnetometer/compass. That should output decent dead reckoning. Doing this just with the gyroscope will work very well for short movements, but it will be close to useless on long, gentle curves. Unfortunately, those MEMS gyroscopes drift quite a lot over tens of seconds. Not a problem if you can do sensor fusion with the magnetometer (reckoning) and the accelerometer (where is "down"), but the latter can't be used on a fast train, acceleration/deceleration of the vehicle and forces in curves make finding gravity challenging. No idea how well a compass works inside a subway tunnel. But maybe I'm wrong, I just have experience trying an "artificial horizon" app on an aircraft - and here, the accelerometer is completely useless for "down". A single maneuver with some Gs and the horizon has no idea what the pitch angle is. Noisy magnetic environment, GPS off? It also doesn't know where it's going.
- porphyra 2y agoI wonder how well magnetometers would work inside metal trains full of electric motors.
- bluGill 2y agoThat is what they are doing. Dead reckoning is generally very inaccurate though, so by recognizing when they are on a train they can greatly increase accuracy because they know exactly where the train is.
- crazygringo 2y ago
- gregoriol 2y agoThis is way too heavy computing, battery consumption, ... while fun engineering, it's very much inefficient to perform
- 0xFEE1DEAD 2y ago@OP how can I get my city added to the app? I was excited to try it out but bummed to see my city isn't listed. It's even more disappointing considering Ulm Germany (with around 100k people) is there, but Cologne Germany (with a population of about 1.1mil) isn't. There are lots of potential users here, especially since the official apps are aweful.
- starlite-5008 2y ago[dead]
- ripe 2y agoCan we take a moment to appreciate the engaging, conversational tone of the writing? The article was a pleasure to read, even when it gets into some weeds explaining the frequency charts, etc. (I read the English-language version). Whoever wrote this did a fantastic job.
- justinko 2y agoYes, the lovely tone of a human being (not AI).
- lallysingh 2y agoI donno which humans you read, but most people I know defecate their thoughts onto a page. Actually good writing takes a lot of effort most people don't do. AI's got a decent baseline.
- justinko 2y agoSure, and I’m not saying we shouldn’t use AI for writing, just that the AI needs to improve.
- vaughnegut 2y agoTheir product release posts and their engineering posts are usually really well written. Transit App is a gem
- yonatan8070 2y agoThis is the first time I'm hearing about it I downloaded it pretty much as soon as I finished reading the blog post, only to discover it's not available in my region :-(
- tgtweak 2y agoI think you can "spoof" gps satellite timestamp transmissions with single transmitter inside the train. This would require on-train equipment but typically the trains know where they are and could translate that into the required gps satellites and timestamp signatures to allow any devices onboard to acquire a "gps" signal and decode the location using timestamp variation. I don't believe any of those are encrypted and transmit ~1000-10000 time per second on 1500-1600mhz spectrum which is fairly simple to reproduce using even a cheap SDR kit. It could also work with 0 input from the train's telemetry - in much the same way as the app - the device would get a reference gps signal (or wifi/BLE when it knows it's in the station), then with a built-in accelerometer (which it has the luxury of direction + stability if it's mounted in the train car) it can determine with greater accuracy where the train is and how far it's moved.
- Aurornis 2y ago> I think you can "spoof" gps satellite timestamp transmissions with single transmitter inside the train. Spoofing GPS as a commercial operation is a quick way to get your company crushed by regulatory agencies.
- bluGill 2y agoI think there should be regulations that allow sending real GPS from low power ground based system. Sending incorrect GPS is a major problem, but a lot of location issues would become much easier if the owners of buildings would just install cheap GPS transmitters.
- acc_297 2y agoIt seems like this functionality could be tacked on to "MSA" which I just learned is an FCC mandatory technology for most cell phones https://en.wikipedia.org/wiki/Assisted_GNSS https://en.wikipedia.org/wiki/Assisted_GNSS
- cruffle_duffle 2y agoI mean obviously you’d set it up through the proper channels. I’m sure there is a regulatory framework for doing exactly this sort of thing already.
- ingen0s 2y agoThis is why I open this site everyday several times a day
- zephyreon 2y agoAs a user of Transit (thank you for such a great app!) this was always one of my biggest annoyances. Not just transit though — with any app that supports navigation on public transit (looking at you Apple Maps). I figured someone was working on this but it’s so refreshing to read about the thought and level of detail that went into your design. What an effort too! Congratulations transit team, you all should be so proud for solving what I’d imagine is one of transit’s largest small gripes.
- bsimpson 2y agoI live between stations. One is a nicer walk; the other is a shorter walk. I check the next train when I leave to see which station to walk to. Would be useful if I could teach this to your app.
- mateobelanger 2y agoTest
- 333c 2y agoI used this feature in the New York subway last week. I didn't know it was new. It's a cool idea, but it didn't work for me. The app said that the train was several stops behind its actual location.
- yonran 2y ago> It now makes the right location prediction 90% of the time. I’m curious about the failure cases. Are they caused by exceptional circumstances, such as the train moving more slowly than normal or skipping a station? Or when you unexpectedly catch an express train or go the opposite direction? Does the algorithm know that it doesn’t know where you are, or does it confidently tell you the wrong station until the GPS is acquired?
- Lance_ET_Compte 2y agoFor the express vs. local, sometimes it will ASK me what train I am on. When there are delays that cause trains to be closer together, it does this. I presume they are crowd-sourcing some data instead of trying to only use an algorithm. I do love this "Transit" app though.
- 30blay 2y agoGreat question! I'm one of the developers behind this project and your guesses are good. Other difficult cases include trains stopping between two stations (doesn't happen everywhere, but it's frequent in NYC), or a user walking fast onboard a moving train, which can be mistaken for the user having gotten off the train. Taking a train in the opposite directions will break the assumptions we make and we won't know until the next GPS location
- clarkmoody 2y agoAlternative title idea: "Instead of Reaching for AI, we used Good Old-Fashioned Engineering to Solve a Tough Problem"
- alanbernstein 2y agoIs machine learning old-fashioned already?
- ant6n 2y agoMachine learning is part of AI.
- riffic 2y agowould love to use collective sensor data to shame operators who accelerate or brake too harshly. that's kind of my transit annoyance these days.
- admax88qqq 2y agoI find the bus tracking of this app in my city is pretty poor unfortunately. Probably not the apps fault probably an issue of the municipality but still annoying. That being said, if this app could convince cities to also be used for payment that would be a game changer. Uber for public transit would really remove so much friction from using transit.
- 43920 2y agoThey do support payment in some cities (mine included), and it works pretty well. A bunch of the larger / better-funded systems are also moving to just accepting credit cards directly on the readers, which is even easier.
- jer0me 2y agoSome cities let you pay with contactless credit cards (at least London and New York have it; Boston and San Francisco are working on it) which seems like the most elegant solution to this, at least from a commuter’s point of view.
- ladams 2y agoYou can pay in the app on the Denver RTD system!
- admax88qqq 2y agoAwesome!
- lacoolj 2y agoThe timing of this post is nuts. I was thinking about a post-apocalyptic future last night (as one does) and wondered if using the gyro on your phone would suffice if the initial location and full map was already available. I think the answer is still unclear since they are using pre-determined routes (easier to track east -> west or east -> southwest than it is east -> north -> south -> north -> east again). But this is very cool that they have so much of the work done already. Maybe even all of it? I don't have the code to look at so ¯\_(ツ)_/¯ Either way, still freaked out they read my mind lol
- showerst 2y agoThis is called inertial navigation, and it works over short distances but then breaks down due to cumulative error. This is a pretty cool use case though since as you said it would be much easier over a fixed route.
- nycerrrrrrrrrr 2y agoGreat article, I'll have to try it out next time I'm on the subway. One correction though - there is no subway line that goes across the Queensboro.
- sailfast 2y agoI appreciate that this is not a mass surveillance play and all of the data stays on your phone. Well done!
- ipython 2y agoSo true. This is the sort of thing that is so exciting from a usability and engineering standpoint. Until some marketer gets their hands on it and decide that they can increase the ROI on microtargeting advertisements by 0.1% if they use this data. Suddenly, we continue to slide into the advertising and propaganda driven attention economy dystopia. Here's to the future!
- jacooper 2y agoGoogle maps(wuth google location service) is alao crazy accurate underground somehow.
- armada651 2y agoWhy all the complicated detection? The user already knows whether or not they are on a train, you don't need to tell them. Just show the predicted location of the train they should be on separately from their last known GPS position. Of course it would be difficult to market that alone as a novel innovative AI feature.
- patrickmcnamara 2y agoTrains at my U-Bahn station are as frequent as every two/three mins sometimes. There is no "the train they should be on".
- armada651 2y agoRight, but the vibration detection isn't used to detect which train they're on according to the article.
- IIAOPSW 2y agoA few thoughts come to mind. Some said others not. 1. Seems a bit weird to be looking at the accelerometer data yet miss the obvious approach of summing up the acceleration to get the velocity and then summing that up to get position. Yes I know about drift but even then I'd assume the fairly constant several-second g force of pulling in or out of a station or taking a curve would be a strong signal easy to distinguish from short lived jostling. 2. The "train moving" frequency you discovered via fourier analysis was most likely the hunting oscillation. This has to do with how the wheels of the train are designed to force it to turn opposite to any deviation from the direction of the track. Thus there is a back and forth "hunting" for the center that is completely determined by the geometry of the track and the wheels, and therefore the length of track per complete back-and-forth cycle (aka the wavelength) is constant. The frequency of the oscillation (aka back-and-forth cycles per second) is just this constant length divided by the velocity of the train. This fact could be leveraged to estimate the actual train speed rather than just moving/not moving. 3. Combining 1 and 2, a combination of integrating acceleration and confirming / correcting estimated velocity with the expected hunting oscillation would likely be the most powerful / reliable model. 4. Using a classifier seems overkill here. But I'm sure at some point it was easier to just raw-data it than work out a theory driven model which accounted for all the practical confounding factors.
- ezfe 2y agoYou still need to know when they are on a train, because you need to know what time they got on the train and started moving. You also have to assume that GPS has already been lost at this point, so you have to do it from the departure location of the train at the right time.
- cenamus 2y agoThat's just an inertial nav systems, quite useful for missiles before/without usable GNSS, but also probably quite inaccurate with the MEMS accelerometers in phones. https://en.m.wikipedia.org/wiki/Inertial_navigation_system https://en.m.wikipedia.org/wiki/Inertial_navigation_system Semi-related but just as fascinating: https://en.m.wikipedia.org/wiki/Terrain-following_radar https://en.m.wikipedia.org/wiki/Terrain-following_radar
- 2y ago
- CarVac 2y agoI'm trying this out literally right now and it got fooled by an unscheduled stop due to train traffic. It thought we were already at the next stop and took a bit to get its bearings again. At least in NYC it should listen for door beeps.
- ekzy 2y agoCould you also pick up the audio announcements? Could be weird for the app to request microphone permission though, but I think lots of lines have them and should be doable to transcribe them locally on the phone. I think your approach is better and simpler, but as I was reading the edge cases (like someone changing train and going back in the other direction), the audio could maybe help getting from 90% accuracy to 98%. Sounds a bit more involved to implement though.
- brirec 2y agoThis was really exciting to read, but after trying it on four NYC MTA commutes (with one transfer on each commute, so a total of 8 different train rides) over the past couple of days I’ve given up on Transit App for now… Yesterday night and this morning it kept telling me to get off the train either two early or too late, and this evening it didn’t even think I got on the L in the first place. The app even lightly scolded me for “missing” my train!
- brewdad 2y agoI’ve given Transit App a few tries on various visits to New York. I always end up back at Citymapper. For me, it works so much better.
- MagicMoonlight 2y agoI thought it was just going to count the stops to figure out where you are. If it has stopped 12 times then you would assume the next stop will be the 13th stop. Then you’re not reliant on schedules.
- barnabee 2y agoTrains often stop between Stops, at signals
- Avlin67 2y agothis is dope. my chinese GF loves it so much. so impressive.