On Fri, 11 Apr 2008, Mr Thant wrote:

On 11 Apr, 19:04, Tom Anderson wrote:

Provided that the bus can get good GPS and GPRS signals. GPS is
notoriously inaccurate in built-up areas, as buildings block lines of
sight to the satellites, and introduce reflections which confuse the
receiver (like ghosting on the telly). I wonder what they're doing to deal
with this?

I've read a TfL paper that I can't find right now that found it to be
surprisingly accurate, something like dead on 98% of the time.
Presumably to do with being aerial mounting a large antenna on the bus
roof where it has a good view of the sky, rather than the tiny
internal one in consumer gear that gets blocked by the car roof.

Sounds plausible. Also, you don't need an accurate fix all the time: even
if you can only get one every fifty metres, it might do; you could fill in
with dead reckoning in between.

tom

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