Le 09/03/2011 10:29, Invisible a écrit :
> 
>>> GPS is only accurate to a few hundred yards of course,
>>
>> Uh, no. What are you smoking?
> 
> Hey, the satellites are 20,000 km up in the sky. It's astonishing that
> GPS can even figure out which city your in, never mind fixing your
> location to a few hundred yards.

GPS computation is accurate, with military access, to less than a yard.
One of its military purpose is guiding rocket/missile between buildings,
with a flight near the ground as close as possible to avoid radar detection.

Civil usage of GPS is accurate to 30 yards/meters.

Some area are covered with DGPS, an additional signal on radio which
provided the offsets measured between the GPS signal and the actual
location of reference points (so that a civil application can compensate
the delta...)

Remember that GPS is operated by the army of the USA (or whatever you
name it), and they can switch it down whenever they want. (or rather,
keeping it on only for the happy fews with the unscrambling devices...)

-- 
Software is like dirt - it costs time and money to change it and move it
around.

Just because you can't see it, it doesn't weigh anything,
and you can't drill a hole in it and stick a rivet into it doesn't mean
it's free.

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