How can you track your location on the subway, where GPS isn't available?
The development team behind the route guidance app Transit posted a blog about how they worked to properly display your current location on the subway when GPS isn't available.
Transit | No GPS required: our app can now locate underground trains
https://blog.transitapp.com/go-underground/
Since subways cannot receive GPS satellite signals, you cannot use GPS to find your current location. In the case of route guidance apps, the current location will jump, as shown in the video below.
If you're familiar with the area, it's fine if your location jumps around a bit, but if you're new to the area, you have to desperately look out the window for the station sign every time you get close to a station. To address this issue, the Transit team began looking for a way to get around without relying on GPS.
The development team focused on 'acceleration.' Modern smartphones come equipped with an acceleration sensor as standard, and acceleration data can be used by apps. The team created an app that reports the 'current state' as shown in the figure below, and collected acceleration data with state labels such as 'walking,' 'using the stairs,' and 'riding the train.'
The collected acceleration data looks like this.
By training an AI model based on the collected acceleration data, it is possible to determine whether a person is on a moving train or whether their smartphone is simply vibrating.
Now that they could determine the user's current state, the team prepared another AI model that could determine the current location based on the user's state, as well as the last GPS location and elapsed time, and train timetable data.
As shown in the figure below, there are places on the subway where GPS signals can reach, so by appropriately correcting the location and displaying it, the accuracy of the predictions has reached 90%.
Both of the models developed by the team can be run on smartphones, so there is no problem even if the Internet is not available. The following movie shows the actual accuracy, with the real position being the 'X' mark, and the predicted results of the AI model being displayed in 'Mixer v1', 'Mixer v2', and 'Mixer v3'.
The blog said to 'try it out using the app,' but unfortunately, at the time of writing, it seemed that it was not available anywhere in Japan.
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