GPS technology - or is it?
 

For those who are aware of what's going on in London re public transport, Crossrail is about to set it's TBM's burrowing away (all 8 of them I think) under the capital.
What mystified me is the BBC report which says:
GigaHertz satellite transmissions are not exactly acclaimed for their reception underground. :Confused:

Obviously the GPS is tracking the location of the Control room, not the TBM... :D

I now have visions of a "war of the worlds" style control room stalking across London on very long legs. :ROFL:

hmm possible with the right equipment, theres a special system called gps underground - title says it all really,

but ive been in the control rooom of the special undeground which runs beneath the normal system and is used by the PO to transfer money and mail across the city and they could track trains without gps on a huge wall monitor.

Depends on how sensetive the aerial is too I suppose. But it's probably more to do with initial GPS readings and sensitive gyroscopes I'd have thought.

Maybe I'm not up on the technology, but I thought Lasers were the main means of measurement/alignment in such projects.
Though I imagine you could have some sort of system based on "GPS technology" with purely local transmitters & receivers I guess.

I'll ask my daughter when I see her this weekend, she's a Civil Engineer and does this sort of thing for a living. (though she may not be too "compos mentis" as she has an all-day corporate event at Twickenham on Saturday where she's an "honoured guest" of some sort :ROFL: )

The train location is easy.....

The running rails (train wheels on them) carry a low voltage current for signalling, they are in insulated lengths & the train axle completes the circuit, thus showing where it is on the schematic. (taken back by the trackside wiring....

primitive but effective..