Richard B. Gilbert 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.

The US government dropped the "Selective Availability" accuracy
degrading function from the GPS signals in 2000. Standard civilian GPS
units are now accurate to within about 50 feet on average. Newer units
with WAAS (Wide Area Augmentation System) capability, originally
developed for air navigation, are accurate to within 10 feet or better.

http://www.ngs.noaa.gov/FGCS/info/sa...statement.html

> As far as I know, a cell phone tower has no means of determining the
> direction your signal is coming from.

By triangulating signals from three towers, the location can be
determined fairly accurately. Obviously, there must be at least three
towers within range for it to work. Other methods use one or more towers
and time based signals to determine locations with varying degrees of
accuracy.

--
Dutch