Setting up a GPS Unit
and Basic GPS Mapping Techniques
Manual
1
Introduction
This manual is intended to provide users with a basic understanding of a Garmin eTrex GPS receiver
and how it can help to support day to day operations. For detailed information about this receiver, refer
to the owner's manual that is included with the receiver.
1.1
What is a Global Positioning System?
The Global Positioning System is a space-based global navigation satellite system. It provides reliable
location and time information anywhere on Earth and at all times when there is an unobstructed line of
site to at least four GPS satellites. It was created by the U.S. Department of Defense in 1973.
1.2
How it works?
The Global Positioning System consists of three segments:
1. Space Segment
The space segment is composed of orbiting satellites positioned in medium Earth orbit at an altitude of
approximately 20 200 kilometers (12 550 miles). The satellites orbit around the Earth in six circular
planes broadcasting the signal from space. Each satellite makes two complete orbits each day. About
eight satellites are visible at any particular time from any point on the ground.
2. Control Segment
The Control Segment is composed of:
•
Control Stations
•
Dedicated Antennas
•
Dedicated Monitor Stations
The control segment tracks the flight paths of the satellites and regularly contacts each satellite with a
navigational updates.
3. User Segment
The user segment is composed of tens of millions of users on-the-ground, in-the-air, water etc.
