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!