"Kwyjibo" <kwyjibo@[EMAIL PROTECTED]
> wrote in message
news:pI2dnc8eQMK_-oTVnZ2dnUVZ_gmdnZ2d@[EMAIL PROTECTED]
>
> "Atheist Chaplain" <abused@[EMAIL PROTECTED]
> wrote in message
> news:RF7Sj.6489$ko5.3857@[EMAIL PROTECTED]
>> "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,
>
> And your navman and tom tom have slightly better GPS antenna, and don't
> have a 3G transmitter sitting right next to them causing interference.
>
>> 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.
>
> I've turned mine off, but definitely saw quicker lock times for the
short
> period I had it active.
>
> --
> Kwyj.
>
My Tom tom is in my phone :-)
I have an N80i with the Tomtom for symbian installed and I use a $12 Holux
Bluetooth GPS receiver to get the signal, it works a treat, I tested it
out
in ****ney a while ago and the only gripe I have with it is its route
selection, the Navman ****s all over it in that regards IMHO.
--
"Calling Atheism a religion is like calling bald a hair color."
Don Hirschberg
|
