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.

That'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.

There should be - everyone on the train wants connectivity. Even if there is wifi on the train, that wifi needs something to connect to.

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. :)