Lowrance electronic GLOBALMAP 3000 - Manual (Page 11)

7
GPS OPERATION
NOTE: A LGC-12S GPS module or an external GPS receiver with NMEA
output must be attached to this unit in order to use the position and navi-
gation features.
WARNING!
Use this product only as an aid to navigation. A careful navigator never
relies on only one method to obtain position information.
CAUTION
This GPS receiver (like all GPS navigation equipment) will show the short-
est, most direct path to a waypoint. It provides navigation data to the
waypoint, regardless of obstructions. Therefore, the prudent navigator will
not only take advantage of all available navigation tools when travelling to
a waypoint, but will also visually check to make certain a clear, safe path
to the waypoint is always available.
INTRODUCTION TO GPS
The Global Positioning System (GPS) was developed by the United States
Department of Defense as a 24-hour a day, 365 days a year global navi-
gation system for the military. Civilian availability was added (but with less
accuracy) using the same satellites. Twenty-four satellites orbit the Earth.
Three of these satellites are spares, unused until needed. The rest virtu-
ally guarantee that at least four satellites are in view nearly anywhere on
Earth at all times.
The system requires three satellites in order to determine a position. This
is called a 2D fix. It takes four satellites to determine both position and
elevation (your height above sea level - also called altitude.) This is called
a 3D fix.