[OSM-talk] Good deal on Garmin GPS unit

[Nick Black]

On 7/5/06, J.D. Schmidt <jdsmobile at gmail.com> wrote:
>
> Nick Black wrote:
> > On 7/5/06, Andy Armstrong <andy at hexten.net> wrote:
> >>
> >> On 5 Jul 2006, at 10:24, Dan Karran wrote:
> >> > - it's rather large compared to my eTrex (though it's relatively
> >> > light)
> >>
> >> Huge, innit? :)
> >>
> >> > - it didn't manage to get a lock on 3 satellites whilst walking to
> >> > work, whereas I think my eTrex does... I should really have waited to
> >> > let it get a lock before walking, but I was late already  :)
> >>
> >> Mine took nearly half an hour to get its head together - I thought it
> >> was faulty. Eventually it worked where everything was and now it gets
> >> a fix within < 1 min from power up and gets a +/- 4m 3d fix shortly
> >> thereafter.
> >
> >
> > GPS units can't actually locate themselves anywhere on the Earth.  They
> > need
> > to know at least which quater-sphere they are in to be able to carry out
> > the
> > regression necessery to determine their position.  That's why the first
> > time
> > you use a unit (or if you turn it off, travel a significant distance and
> > turn it on again) it takes a while to sort itself out.  My Garmin GPS 60
> > took a good 15 mins to determine my position the first time I turned it
> on,
> > and I even told it I was in London.
>
> If your GPS takes 15 minutes for a first fix, something is wrong with
> it, especially if it is a newer GPS. What you might be thinking of, is
> the fact that it will take about 15 minutes to get a complete ephemeris
> and almanac down. But the GPS should be able to provide a first fix and
> be able to provide navigational data long time before that.


First fix from a totally cold start?  The last time it was turned on was in
Taiwan, then in London.  Do you have a Garmin unit?


> Units with teh Sirf Star III chip
> > shouldn't have this problem as they using GSM cells to locate themselves
> as
> > well as GPS satellites.
>
> Oh ? Thats a new one. The SiRF III chipsets are NOT GSM enabled, and do
> not contain any logic that allows it to pick up GSM cell transmissions.
> Some multifunction devices that use SiRF III chipsets for the GPS
> functions contain additional logic in order to communicate via GSM for
> updated trafficdata/use as a cellphone, and they might be using the GSM
> cells for additional locationpositioning.
> But saying that "Units with the Sirf Star III chip" are using GSM cells
> is not correct.


Thats what I thought until I someone pointed out this article to me:

http://www.sirf.com/Downloads/Collateral/GSC3(f)_6.20.05.pdf

and another that I can't find at the moment, think it was on Sirf's website.

Its about all the documentation I could find about Sirf Star III, the
mention of GSM is a *bit* flakey - the chip must at least be compatible with
GSM receivers then?


Nick

J.D. "Dutch" Schmidt
>
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