Comment by esafak

It's very easy since there is limited ability for trains to change tracks, so the location history of the train is a strong indicator of which track it is on. Even Google Maps can tell you which lane you are in since god knows when, and cars can freely change lanes. And that's just consumer software. For something commercial like a train they could trivially solve this problem with something more robust. But I'm not familiar with the Spanish system; how much of the engineering did they do?