How Gps And Cartography Work - Humminbird 757c Operation Manual

531528-1_A - 757c_787c2_&_787c2i_Man_Eng.qxp

How GPS and Cartography Work

Your 700 Series™ Fishing System also supports GPS and chartplotting, and
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
+/- 10 meters, depending on conditions. This means that 95% of the time, the
GPS receiver will read a location within 10 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.
The GPS Receiver included with your 700 Series™ Fishing System allows you
to cosmbine easy-to-use FishingGPS® chartplotter and navigation capabilities
with advanced fishfinding.
GPS uses a constellation of 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.
6
10/16/2006 10:41 AM Page 15