Appendix B--GPS Satellite Reception
The Global Positioning System (GPS) is a system of 24 satellites that circle the Earth
twice a day in a very precise orbit and transmit information to Earth. The StreetPilot
must continuously receive signals from at least three of these satellites to calculate your
location and track your movement. At times, additional satellites may be needed to
determine your location.
Your GPS receiver can only receive signals from satellites which are above the hori-
zon, so it needs to know what satellites to look for at any given time. In order to deter-
mine which satellites are above the horizon, your GPS needs to either be told its general
location (“initialized”) or given the opportunity to find itself. Once you initialize the
unit to a location, it will typically compute a position within a few minutes.
Initialization is only necessary under the following conditions:
•
The first time you use your StreetPilot (new from the factory).
•
After the StreetPilot has been moved more than 500 miles (with the power off)
since the last time you used it.
•
If the StreetPilot’s memory has been cleared and all internally stored data has
been lost.
Because the StreetPilot relies on satellite signals to provide you with navigation guid-
ance, the StreetPilot needs to have an unobstructed, clear view of the sky for best per-
formance. In a nutshell, the GPS receiver’s view of the sky will generally determine how
fast your location is determined—or if it is determined at all. GPS signals are relatively
weak and do not travel through rocks, buildings, people, metal, or heavy tree cover, so
remember to keep a clear view of the sky at all times for best performance.
Once the StreetPilot has calculated your location, you’ll usually have anywhere from
five to 12 satellites in view. The receiver will then continuously select the best satellites
in view to update your location.
appendix b
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Summary of Contents for StreetPilot GPS
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