"Doug Jewell" <ask@[EMAIL PROTECTED]
> wrote in message
news:48185535$0$9716$5a62ac22@[EMAIL PROTECTED]
> Atheist Chaplain wrote:
>
>> how can aGPS help you to lock on to a satellite signal any quicker ??
> It's inherent to the way GPS works. They constantly transmit a signal
that
> includes the time according to the satellite's atomic clock, and also
the
> satellite's postion. The receiver uses the time taken for the signals to
> reach it to determine the distance from the satellite. Using a bit of
> math, as long is it knows the distance to 4 or more satellites, and the
> position of those satellites, it can triangulate. But there's a catch -
> the satellite transmits this data at a fairly low bitrate, and so it
takes
> 30 seconds for the whole data packet to be transmitted. In a best-case
> scenario, it will take 30 seconds to get the position information from
the
> satellite, but if the signal is interrupted, corrupted etc during this
30
> seconds, the GPSr doesn't know where the satellite is, so it can't
compute
> the position accurately (or at all). This can cause delays in getting a
> fix of sometimes several minutes. Additionally, the satellite position
> data can be up to 2 hours old, and it takes approx 12 minutes for the
> entire catalog of satellite data to be downloaded. Until this is
received,
> the accuracy of the fix can be poor.
> To speed this process up though, and to get a more accurate fix, some
> GPSr's allow you to download predicted satellite positions. Because the
> GPSr already knows the satellite position, it only needs the timecode
from
> the satellite, not the whole packet. This allows a faster, and more
> accurate fix.
>> that's just another rort by the Telco's to extort money from the
>> gullible, I though aGPS was to download things like voice direction and
>> POI's (things that were intentionally stripped out of the Telco
supplied
>> GPS software so they could then charge you for it at exorbitant data
>> transfer fee rates)
>>
while that may be true I have yet to see a time when my Navman GPS doesn't
see at least 5 satellites and currently my Tom tom phone system is
tracking
9 sats. Admittedly I'm not in the concrete jungle of ****ney but even when
I
am, the only time I have lost signal was when I was in one of the tunnels.
to be fair I have never been driving so fast in ****ney that the GPS
couldn't keep up with my position so I fail to see any benefit from aGPS.
--
"Calling Atheism a religion is like calling bald a hair color."
Don Hirschberg
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