[pct-l] Question about Halfdmile App

[Rob Flynn]

<<  FYI:  Apple Store Genius Bar told me that the iPhone's GPS function
needs some cell tower signal to work,  Even when the phone displays "no
signal", if apps using GPS are working, that means some signal is getting
thru from a cell tower in addition to the satellites.  >>

This is not true, but the Genius person was on the right path.  Navigating
on your smartphone (this applies to ALL smartphones: iPhones, Androids,
Windows Phones, etc) can work with or without a cell signal, but will be
much more accurate and quicker if it has a cell signal.  The cell signal
provides Assisted GPS data, which allows the GPS system to more quickly lock
on to the satellites.  This aGPS data will continue to assist your GPS for a
number of days afterwards, even if you are in airplane mode and are
receiving no data from the cell signal.  You should use your smartphone's
navigation app in town at least once a week, while you have cell or WiFi
data access, to allow it to update this aGPS data cache and provide better
GPS functionality when you get back into the boonies, where you have no data
access.  This aGPS cache lasts somewhere between 5-7 days on most phones, I
believe (would love to have some confirmation of this).

For more information, read this:

http://en.wikipedia.org/wiki/GPS_enhancement

And, more specifically, this:

http://en.wikipedia.org/wiki/Assisted_GPS

Long story short, if you take one thing away from this discussion, make sure
you use your smartphone navigation app at least once a week, in town, while
you have signal.  This will give you fasters locks later, when you have no
signal.


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