GPS

From TreoCentral

GPS stands for Global Positioning System, which is system for determining a user's latitude and longitude, which can then be used by mapping software to aid in navigating from the user's current location to another location. All GPS systems work by tracking signals from a set of 27 orbiting satellites (24 active, with 3 on-orbit spares). At any given time at any location on earth, several of these satellites within range of the user's GPS receiver (though tree cover, tall buildings, or deep canyons may preclude adequate reception.) From the known (but changing) locations of these orbiting satellites and the time delays between signals received from different satellites, the user's position can be determined. These satellites were launched and are maintained by the US government. There is no cost to use them, other than the cost already borne by US taxpayers. There is no need for internet access or wireless phone service to use GPS devices, although all modern cell phones, Treos included, support "Assisted GPS," which use a combination of GPS satellite information and cell tower information to determine the user's position. This information is available to 911 emergency services and is used by some third-party navigation service providers such as Telenav. Detailed explanations of GPS systems are available on many websites such as Wikipedia.

Treos do not have GPS built-in (in fact even TeleNav services on Treos still require an external GPS receiver), but are able to use an external GPS receiver that communicates with the Treo via Bluetooth or a USB cable. There are many GPS accessories, such as GPS receivers, map databases and navigation programs, available for Treos and other PDAs.