Richard B. Gilbert wrote:

> D wrote:
>> On Fri, 04 Apr 2008 21:12:28 -0400, "Richard B. Gilbert"
>> <rgilbert88@comcast.net> wrote:
>>
>>>Roger 2008 wrote:
>>>
>>>>"Gordon Burditt" <gordonb.sh6xy@burditt.org> wrote in message
>>>>news:XrOdnYKg7an-52vanZ2dnUVZ_vOlnZ2d@internetamerica...
>>>>
>>>>
>>>>>>Please do not forget who the original poster was and his questions: He
>>>>>>asked:
>>>>>>"can I display my own LAT/LON values somehow without a map application ?"
>>>>>
>>>>>For some cell phone implementation of "GPS" (this one doesn't involve
>>>>>actual satellites talking to your phone), your position coordinates
>>>>>are present at the cell towers and somewhere in the offices of Big
>>>>>Brother, but not on your cell phone. If a map application can get
>>>>>your position at all, it has to ask your cell provider to send it,
>>>>>and that may cost money.
>>>>
>>>>
>>>>Oh yeah, now that you mention it. My first camera phone called it GPS but
>>>>when you read further about it, it was just using cell phone towers.
>>>>
>>>>BTW I have met a person with an iPHONE that thinks his phone has GPS and he
>>>>even showed me "Google Maps for Mobile" on it.
>>>>
>>>>I thought he had a messed up GPS reading because it had us way across the
>>>>street and then I learned later the iPHONE uses cell phone towers for an
>>>>approximate location on "Google Maps for Mobile."
>>>>
>>>>
>>>
>>>GPS, or at least the civilian version of it, is only accurate to within
>>>about 300 feet or 100 meters. I once did a "site survey" using a
>>>Motorola M12+T GPS timing receiver. The software I used plotted
>>>something like 10,000 position readings on the map. The result was a
>>>strip about 10 meters wide and 100 meters long and oriented ENE-SSW. My
>>>antenna was more or less in the middle of this mess.
>>>
>>>The military uses a different set of signals from the same satellite and
>>>gets accurracy good enough for weapons targeting. This level of GPS is
>>>available only to the military and certain defense contractors. Us
>>>lowly civilians can't get it.
>>>
>>>As far as I know, a cell phone tower has no means of determining the
>>>direction your signal is coming from.
>>
>> Towers cannot tell what direction the signal is coming from, but can
>> tell from relative power how far away it is, and form a circle based
>> on that reading. For sake of argument, say you are 3 miles from
>> tower one, and 5 miles from tower two. there are only two places you
>> can be 3 milies and 5 miles from the towers. Add a third tower, and
>> you only have one place you can be. That is how triangulation (hence
>> the tri - three) works.
>
> I suspect that this technique would yield an uncertainty of position
> that is far greater than that inherent in GPS. For one thing, the
> relative signal strength depends on more than distance!

Yes, the single tower strength method is inherently inaccurate. It is
however better than only knowing which tower a handset is using, the
least accurate, and previously the only method of locating someone
that's lost. Modern GPS/WAAS is by far the most accurate, but the other
methods do have their place as a backup when GPS is not available for
one reason or another...

--
Dutch