Re: [apple-iphone] Directions

> So the iPad GPS radio connects directly with the satellites - makes no use of cell or wifi?

Pure GPS units are radio receivers.

Your iPhone can locate itself even in areas with no Wifi or cellular connectivity, using the GPS radio. If it had loaded map data before losing connectivity, it can even show you its location on the map.

But someone using Find My iPhone won't be able to find you, because the phone has no way of reporting its location, even though it has located itself.

<http://www.ehow.com/how-does_4564296_gps-work.html>
> What do the Satellites do?
> • The satellites send radio signals down to Earth. The signals contain information about each satellite, including the precise time. The GPS receiver receives and decodes that signal.
>
> How Does it Know Where You Are?
> • The time code included in the signal is compared to the precise time kept in the ground unit. By comparing the data contained in the transmitted signal to that stored in the unit, a location can be determined to within 10 to 20 meters. With a secondary antenna, or another receiver slaved to the first, accuracy can be reduced to inches. As long as the GPS receiver can contact at least three satellites on the GPS network, a position fix can be determined; of course the system is designed so that at least three satellites are above the horizon at any given time. The more GPS satellites that a receiver can detect, the greater the accuracy. Often, as many as 8 or 10 satellites can be detected, and the civilian units can offer near one meter accuracy.

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Jim Saklad mailto:jimdoc@icloud.com



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