How is the position of a train modeled in a computer control system?
I can think of two basic approaches but I am not sure which (if any) are used in the real world.
Ex: (-42, 23)
The position of the train is modeled by its real world position. The only issue I could see with this is extra work would have to be done at some stage to determine what track the train is on.
Ex: (20m, Track 34-B)
The position of the train would be modeled by its distance from the start of the track, and the track it was on. This isn't exactly as intuitive right off the bat but I think it makes more sense.
I only ask because earlier I was reading some about PTC and as I was reading this popped into my head.
As brought up by ratchet freak it most likely depends on the sensors on a track.
I was wondering if there is anyone out there who is or currently was part of the development of such a PTC system who could speak to which method is used.
Or if there is a link to a detailed specification of a PTC system (May exist because the conversion of railways is partially managed by the government).
My guess is probably something similar to (Distance, Track) for data gathered by on track sensors and then GPS is used as a fallback which can be converted into (Distance, Track).