How the live map places trains
Also: map, anchor, positions
No train sends its GPS. Trainiac works out where each one is from the signalling, then keeps it moving smoothly.
Example
Berth step
1A23 steps out of the berth at Reading’s platform
Anchor
So it’s just departed Reading, seconds ago
Glide
Along the track towards the next timing point, at timetable pace
An illustration of how anchoring works.
The open feeds don’t include GPS. What they do include is the Train Describer: every time a train moves between signals, its headcode steps into the next berth. Some berths are tied to a station, so a step there means the train just arrived or left.
Trainiac uses these as anchors, best first: a berth step tied to a station, then a berth whose place we learned from watching thousands of trains pass it, then a TRUST report from a timing point.
Between anchors, a train glides along the real track at the pace its timetable expects. It’s always drawn as “this far along the stretch between two of its timing points”, so it stays on the rails and never jumps.
In Trainiac
The live map on traini.ac.