Summary: my smartphone can't do public transport journey planning in underground metro and subway stations because it doesn't know where it is.
Is there a description for cities and public transport agencies how to enable smartphone positioning in underground public transport stations?
My simplest idea is to use Wifi routers. There might be already WIFI routers underground and adding cheap 20 USD routers for the sole purpose of positioning might be suitable. But how do we tell Apple and Google where they are (and in which underground level)?
This question is not about a private indoor positioning system that works only with one app. The smartphone itself should know where it is, including all apps running on the smartphone.
I did not notice this problem in my own city where I memorized the public transport network before smartphones were invented. But testing my own mobility app for tourists in foreign cities, I found that this is a common problem (including in my own city).