Q
Q
Q
Q
Q u
u
u
u
u iiiiiccccck
kk
k
k SSSSSttttta
a
a
a
ar
r
r
r
rttttt
5
The Global Positioning System (GPS) consists of a network of 24 satellites which circle the earth
twice a day in a very precise orbit and transmit information back to Earth. The GPSMAP 295 must
continuously “see” at least three satellites to calculate your position and track your movement. At times,
additional satellites may be needed to determine a position.
By using an almanac (a timetable of satellite numbers and their orbits) stored in the receiver’s
memory, the GPSMAP 295 can determine the distance and position of any GPS satellite and use this
information to compute your position. Your GPS receiver can only see satellites above the horizon, so it
needs to know what satellites to look for at any given time. To use this almanac data, your GPS needs to
either be told its general location (be “initialized”) or given the opportunity to find itself.
The first time you use your GPSMAP 295, it may take several minutes to get a position fix. Because
the GPSMAP 295 relies on satellite signals to provide you with navigation guidance, the receiver needs
to have an unobstructed, clear view of the sky for best performance. In a nutshell, the GPS receiver’s
view of the sky will generally determine how fast you get a position fix—or if you get a fix 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 GPSMAP 295 has calculated a position fix, you’ll usually have anywhere from five to
twelve satellites in view. The receiver will then continuously select the best satellites in view to update
your position. If some of the satellites in view get blocked, or “shaded”, the receiver can simply use an
alternate satellite to maintain the position fix. Although a GPS receiver needs four satellites (or more) to
provide a three-dimensional (3D) fix, it can maintain a two-dimensional (2D) fix with only three
satellites. A three-dimensional fix includes latitude, longitude and altitude; whereas a two-dimensional
fix includes only latitude and longitude.
What is GPS?
The GPS antenna’s view of the sky will determine how fast you
get a position fix, or if you obtain a fix at all. GPS signals do
not pass through obstructions made of wood or metal.
The 24 GPS satellites are constantly moving, orbiting the
earth twice a day. In order to calculate your position, the GPS
receiver needs to continuously “see” at least three satellites.
G P S M A P 2 9 5
ENT
ER
MARK
MENU
NRS
T
ROUT
E
WPT
QUIT
PAGE
OUT
IN
