[OSM-talk] Good deal on Garmin GPS unit

[J.D. Schmidt]

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.

 > 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.

J.D. "Dutch" Schmidt