3
CHAPTER 1 – GNAV20 OVERVIEW
Figure 1. Display Unit
Home
– Pushing the
HOME button routes you
to a predefined address in
memory.
Left
– Moves the cursor to
the left.
Scroll Up/Down
–
To scroll through
menu items quickly.
Cancel
– To cancel the action
and move back one level.
Right
– Moves the cursor
to the right.
Menu
– Display Main
Menu
4
CHAPTER 2 - HOW GPS WORKS
The Global Positioning System (GPS)
is a worldwide radio-navigation system formed from a
constellation of 24 satellites and their ground stations.
GPS works in any weather conditions, anywhere in
the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth.
GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially,
the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received.
The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements
from a few more satellites, the receiver can determine the user's position and display it on the unit's
electronic map.
A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position
(latitude and longitude) and track movement. With four or more satellites in view, the receiver can
determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been
determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance,
distance to destination, sunrise and sunset time and more.
GPS works in the following simplified way:
1.
The basis of GPS is "
triangulation
" from satellites.
2.
To "triangulate," a GPS receiver measures distance using the travel time of radio signals from 3
or more satellites.
3.
To measure travel time, GPS Receiver needs very accurate timing in its circuitry.
4.
A correction must also be made for any delays the signal experiences as it travels through the
atmosphere.
5.
Along with distance, the exact locations of the satellites in space are required for the calculation.
6.
The firmware that runs the GPS Receiver takes all these inputs and calculates the co-ordinates of
the user’s location.