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Ian Stirling napisał(a):
<blockquote cite="mid45F142ED.7080303@mauve.plus.com" type="cite">Bartlomiej
Zdanowski AutoGuard Ltd. wrote:
<br>
<blockquote type="cite">Hello.
<br>
<br>
Nils Faerber napisał(a):
<br>
<blockquote type="cite">
<blockquote type="cite">There is all sorts of wacky stuff - for
example, peer-peer DGPS that can
<br>
be done, where all stationary neos on charge with a GPS signal and a
<br>
free internet connection contribute to a global ionospheric model.
<br>
Then any Neo can connect to this model, download 200 bytes or so, and
<br>
get +-0.3m (or better) position for a short while.
<br>
</blockquote>
<br>
Exactly.
<br>
Also relative positioning can be made much more precise using the raw
<br>
data (AFAIK in the range of cm not m).
<br>
</blockquote>
I asked my colleagues who are GPS devices specialists and they said
that this is all wrong. Military devices can do magic but civil not.
They said that with civil GPS receiver you can get accuracy up to about
5 - 10 meters. For such precision it is required to be seen at least 8
satellites, a clear sky and good magnetic and ionosphere conditions
(also solar magnetic field's change is important).
<br>
</blockquote>
<br>
It's a little more complex than that, and not quite as bad.
<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.mauve.demon.co.uk/gps-average.gif">http://www.mauve.demon.co.uk/gps-average.gif</a> is some data I took a few
years back with a garmin GPS12.
<br>
The circles show radiuses inside which the stated number of points
fall, in a 10 second average.
<br>
For example, 99.99% of points fall within 13.8m.
<br>
10s averages are red dots,
<br>
green 100 second, magenta circles 1 hour, cyan squares 6 hours, and
<br>
black 24h.
<br>
</blockquote>
Try it while walking on streets between buildings :(<br>
Another problem can be when we put Neo out of pocket. I don't know if
it's GPC received would need some extra time to compute pos.<br>
<blockquote cite="mid45F142ED.7080303@mauve.plus.com" type="cite">If a
number of factors in the hardware all come together (that details are
not public on) position under 10cm may be possible after downloading
the few hundred bytes of correction information. (It may be possible to
optimise this down a lot)
<br>
</blockquote>
So *military* devices does it. But not civil.<br>
<br>
<br>
<div class="moz-signature">-- <br>
<b>Bartlomiej Zdanowski</b><br>
Programmer<br>
Product Research Department<br>
AutoGuard & Insurance Ltd.<br>
<br>
<small>
Omulewska 27 street<br>
04-128 Warsaw<br>
Poland<br>
phone +48 22 611 69 23<br>
<a href="http://www.autoguard.pl" style="color: rgb(68, 68, 68);">www.autoguard.pl</a><br>
</small></div>
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