Humminbird 798c, Operation Manual

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6
How GPS and Cartography Work
Your 700 Series™ Fishing System also supports GPS and chartplotting. It uses
GPS and sonar to determine your position, display it on a grid, and provide
detailed underwater information. The Global Positioning System (GPS) is a
satellite navigation system designed and maintained by the U.S. Department of
Defense. GPS was originally intended for military use; however, civilians may
also take advantage of its highly accurate position capabilities, typically within
+/- 4.5 meters, depending on conditions. This means that 95% of the time, the
GPS receiver will read a location within 4.5 meters of your actual position. Your
GPS Receiver also uses information from WAAS (the Wide Area Augmentation
System), EGNOS (the European Geostationary Navigation Overlay Service), and
MSAS (the MTSAT Satellite Augmentation System) satellites if they are
available in your area.
GPS uses a constellation of over 24 satellites that
continually send radio signals to the earth. Your
present position is determined by receiving signals
from up to 16 satellites and measuring the
distance from the satellites.
All satellites broadcast a uniquely coded signal
once per second at exactly the same time. The GPS
receiver on your boat receives signals from
satellites that are visible to it. Based on time
differences between each received signal, the GPS receiver determines its
distance to each satellite. With distances known, the GPS receiver
mathematically triangulates its own position. With once per second updates,
the GPS receiver then calculates its velocity and bearing.
How GPS and Cartography Work