GPS had been in operation for many years before they turned off encryption so civils could get full res from it. Up to that time the civil one had degraded resolution and only US military had access to the full resolution. That's how the system was designed. Presumably they could go back to encrypting the signal again if they wanted.
I think they only dropped the encryption because the commercial products were getting good resolution anyway. They had come up with various ways to improve accuracy before the encryption went.
There were local services which transmitted the error, coining the term Differential GPS:
Very rough due to multipath timing errors...
In article , dennis@home scribeth thus
Why did U use one when a boy scout then ?..
Yep Den!, you'll just have to have the law's of physic re writ;)...
No!, Really?...
>
I thought they worked by measuring the relative field strengths from whatever they could pick up, and triangulating from that. As you say, a
*very* rough guess. Better than nothing, though....
Thats verging on the impossible in Urban areas and not that simple either in rural ones...
Well we do use "Followus" which on Vodafone can track a mobile phone within some 300 to 400 metres depending on location and the number of base stations in range..
Which won't be that many in rural areas!..
Which are?..
But your still depending on Satellite transmissions which in urban areas can be very difficult to receive..
Humm;!...
Inmarsat:- System Specifications:
GPS:-
1575.42 MHz (10.23 MHz × 154) called L1; and a second at 1227.60 MHz (10.23 MHz × 120), called L2.
Agreed, but I think the Galileo operate at a higher power than GPS, though I could be wrong....
Budget cuts, don't you know.
I'd be quite interested in doing it too, but I haven't been caught speeding.
The police like it because they get a cut of the course fees, but they don't get anything from the speeding fines. This has caused them to allow significantly more leeway before fining, and to use the cut from the course fees to help keep some speeding cameras running after local authorities removed funding.
When I started working in North London in 1983, there used to be a pair of variable message boards on the A414 approaching the Park Street M10 roundabout. I recall seeing two messages capable of being displayed, "QUEUE AHEAD" (there is a brow of a hill which hides any queue for the roundabout), and "TOO CLOSE" which flashed up when it detected tailgating. Not long afterwards, the signs stopped working, but remained there for several years non-functional. (Checked on google streetview, and they've been replaced now by permanent Queue Ahead warning signs.)
That was nearly 30 years ago, so it's clearly possible to do it.
There was a system to detect tailgating on the approach to Windsor Great Park going back for a similar time.
Chris
Right well thats still trying to get awkward frequencies through urban obstructions..
And then if you have or need land based transmitters thats a lot of base stations to penetrate built up areas to mobile powered devices unless use if made of the GSM network...
Well it might but even say 3 dB higher isn't going make that much difference..
IME GPS technology has a variable amount of accuracy depending on several factors.
My father went on one of those courses and said he found it useful. The only problem was that he had to attend the course where the speeding offence was committed rather than a local one.
On a busy road it's probably accurate to have a permanent "too close" message because there will always be someone tailgaiting.
They can totally fail when a lorry driver with a GPS jammer goes past.
Can't have the "wrong" constabulary getting the kickbacks ...
You are supposed to be able to do it locally, *if* your police force runs them.
In article , Mark scribeth thus
Right .. examples then?...
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