In message , charles writes
Of course they have a way to find themselves - it's called GPS :-)
Phones have an advantage over standalone GPS/satnav units in that they already know roughly where they are (I assume down to the 100's of metres at least) from the cell towers they are connected to, so the using GPS it can located itself quickly.
My handheld GPS unit does take noticeably longer to locate itself if it has moved a long distance switched off, however, it does locate itself fine.
Inside a metal box in a pocket or bag is not a good place for reception of the very weak GPS signals...
GPS units can work out where they are from cold but it can take a several minutes even with the receiver stationary and with a clear view of a lot of sky (thus satelites).
I suspect the aquisition time varies from receiver to receiver. It would be reasonable to assume that one on a car is powered all the time, thus aquisition time isn't a issue. A handheld walkers one on the other hand needs to aquire quickly, when taken out of the rucksack and switched on from cold in a carpark miles from where it was last used the previous weekend.
They can also use GPS-A to download the satellite almanac over the phone or wifi network so they know which satellites should be overhead, rather than having to find out from the satellites themselves.
When I use the channel tunnel, my sat nav has usually worked out where it is before I get to the top of the ramp leading up from the platform.
Our one was switched off for maybe ten minutes. The only reason it was lost must have been too much building surrounding the car, but it should surely have remembered where it was.
In message , Davey writes
Yes, it should have performed better than it did
AFAICR mine normally locates itself quickly on the otherside.
Taking it a ew hundred miles truned off and it takes a while longer
It should but if the cars mapping/route finding bit expects the GPS module to be always powered up or have a very rapid aquistion time when it gets switched on the mapping bit has no reason to remember last location.
Things that extend the aquistion time are poor signals (urban canyons, foliage), only a small number of satellites visible, a "long" time since last good fix, moving the Rx when it's trying to aquire a fix, moving the Rx powered off.
But once the GPS module has got a fix (might take 5 or ten minutes if driving through urban canyons) the mapping side ought to sort itself out.
The problem for us was that we wanted to know how to get from where we were back to the M25! We had followed it faithfully going round and round the one-way system to the destination, which was next to a tallish building, and we had no idea how to get out, as the road we had followed was one-way. Eventually, we went back to the Avis office and asked, and in fact got bad information from the girl there! Eventually, after following our internal brain-maps (it must be that way), we saw some road signs to the M25, at about the time that the GPS finally got its brain unscrambled. Yes, it did sort itself out, but it failed its initial function of sending us in the right direction to start with (as did the girl).
you mean the one on the motorway services?
Nice there innit!
tim
No, right in the town centre. Walk to about fifty different restaurants/bars.
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