The GPS satellites carry only enough propellant for small corrections and orbit at about 12,500 miles. Spy satellites used to (probably, in the main, still do) carry much more fuel (to sustain height and to change orbit to cover different areas) and orbit at a few hundred miles, for detail of pictures obtained.
While it is certainly possible that GPS satellites also carry spy cameras, it seems unlikely, being high up and stuck on fixed orbits.
Just don't drive near an airport:
GPS worked flawlessly today. Sigh.
I heard they can deliberately degrade them, to prevent the enemy making use of them, for missile delivery. Perhaps that's what they did?
And how many people apart from Turnip are complaining of degraded access right now in this bit of the UK?
since only tim lamb is even close, no one else on uk-d.i.y would be affected. it's fine today...
They used to have "Selective Availability", they declared they won't use that again, and newer replacement satellites are supposedly incapable of using it ...
The problem was people managed to work out where they were to a meter or so even with the 'civilian degradation...'
You can get GPS RTK modules for about £300 that give you 1cm precision relative to either your own base-station, or to a commercial network of base-stations.
er. I call that 50 miles or so:-)
>
I have never had similar experiences with my satnav. Probably because it's better than your unnamed one.
My journey finished well south of Royston....
It's TOM Tom go on a Samsung smart phone. Streets ahead of anybody elses expensive s*it.
It has worked perfectly for 6 years
Yes, but charles was talking about TV signal and a local earth plane is even less relevant to satellite signals.
But the samsung smartphone gps reciever may well be dying.
All you need is to know the exact position of somewhere and compare it with what the GPS is saying.
The US used to switch GPS between 10 and 100 metre accuracy. I vaguely remember it was Clinton that stopped it (not personally).
Differential GPS. You calculate the difference between the GPS provided location of a fixed reference point and your GPS provided location. You usually transmit the fixed to the mobile with a radio link.
Simple in principle. But both receivers need to be seeing exactly the same satellites, which is tricky/impossible to do with COTS equipment. Hence the cost.
(Pre-GPS, we'd lug a pair of lorry batteries to remote clifftop locations to power two or more Decca Trisponders for maybe a couple of days. These used time-of-flight coded pulses picked up on the survey vessel. Lots of TTL. Later, I automated this by hooking the receiver to an HP-85 via a GPIO card and wrote HP BASIC software to plot position every second on an A3 flatbed plotter. The first time, the skipper couldn't get the hang of steering when the plotter was going 'backwards' until I made a tiny paper boat which I sat on the plotter pen and rotated as needed. Lightbulb moment for skipper.)
In message snipped-for-privacy@pvr2.lan, Rod Speed snipped-for-privacy@gmail.com writes
I'm pretty sure that there have previously occasionally been localised military trials to test the effectiveness of disruption to GPS signals - prior to which have been announcements to warn members of the public that they should temporarily not rely on their satnavs to give correct readings (or even to work at all).
But it is much more likely that the turnip's smartphone is at fault than he happened to encounter another trial like that which didnt have any warning to the general public that GPS was being deliberately compromised that day.
I think RTK takes DGPS to the next level, it's what makes those aerial LED drone displays possible
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