[aprssig] APRS iPhone App

[Tom Hayward]

> Does the iPhone have an ACTUAL GPS RECEIVER in it ?; or is it
> simply a Mapping Software that utilizes the CellPhone Towers/IP Service
> you subscribe to ?
> The iPod Touch has "Mapping", but you NEED to have Wireless to make it work,
> it does NOT have an actual GPS Rx.

With minimal study of the iPhone Developers Location Services API, I
believe this is how the iPhone gets a location:

Tier 1 - Assisted GPS. GPS module gets almanac data from cell tower,
then reports a GPS position.
Tier 2 - No GPS. Location triangulated between multiple cell towers.
Tier 3 - No GPS, single cell tower. Broad location area given based on
cell sector (based on which of the cell tower's antennas has the
strongest signal to the phone. I'm not sure if AT&T supports
time-delay-to-tower to determine location from tower).
Tier 4 - Wifi only. Looks up hotspot in internet location database.

iPhone 2 can do Tier 1-4.
iPhone 1 can do Tier 2-4.
iPod touch can do Tier 4 only.

Hope this helps.

Tom KD7LXL