Introduction to GPS Navigation

Introduction• The Global Positioning System (GPS) is a free system available 24

hours a day, 365 days. Its an all weather outdoor system which provides users with:

– Their position on Earth– Their height above sea level– Their speed and direction of travel– The time

• How it works– There is a network of 24 satellites orbiting earth. They each orbit

earth twice a day and at any one time between 4 and 10 will be visible from your location.

– The GPS system was developed by the US military. In the year 2000 the system was made public and more accurate when the “Selective Availability” SA was turned off.

• GPS Satellites– 1st satellite was launched in 1978 with the last being placed in 1994– Have highly accurate clocks which transmit a microwave signal to

earth.– On a cloudless night with minimal backlight the satellites can be

seen orbiting the earth.

• GPS Receivers– The receivers take the information from the satellites and use

triangulation to calculate the user's exact location.– A minimum of 4 satellites are needed for an accurate 3D position.

The more satellites visible by the GPS, the greater the accuracy.– Accuracy is generally within +/- 10m, 95% of the time.– 2 main brands – Garmin or Magellan

• Many different applications (Automotive, fitness, Outdoor, Marine, Aviation)

Features, Functions &Formats

• Features– Robust– Waterproof– Colour screen– Auto routing– Compass

• Functions– Maps– Sun/moon times– Tides– Geocaching– Trip data– Games– Altimeter– Calendar/calculator

• Formats– Distance, speed – Elevation– Time– Position– Datum

GPS UsageThe most common use of the GPS receiver is to get a position fix. When your moving the gps gives you speed and direction of travel.

• Uses: Military & Civilian

Missile guidance, Target tracking, Search & Rescue

Aircraft, Vehicle, Human and Pet tracking

Map making, Robotics, Surveying, Recreation

• Cold Start– The first time you use a GPS receiver or if you’ve moved more

than 300km since you last used it.– May take up to 5 minutes to track satellites and initialise.

• Warm Start• Receiver has recent navigational messages from satellites• Up and running in less than a minute.

GPS Usage - Waypoints

GPS receivers can store positional information as waypoints. These waypoints can be given names, labels, symbols etc.

• Can be stored or entered in one of two ways.– The current location of the GPS can be saved. (Mark)– A waypoint can be manually stored by entering coordinates or

uploading them from a computer interface.

•Navigating to a waypoint– You can use the GPS to navigate to a waypoint using the “Go To”

function.– The GPS will give you the distance and bearing to the waypoint

which it continually updates as you move.

GPS Usage – Tracklogs & Routes

• Tracklogs– This is a breadcrumb trail of your travels, recorded on the GPS– The trackback function can be used to navigate back to a starting

point using the tracklog.– It can be downloaded onto a computer to show where the GPS

has been.

• Routes– It guides the user to a destination via a particular path– Similar to the “Go To” function– Many waypoints make up a route– Can create a route on mapping software and upload to GPS– GPS automatically follows the route, from one waypoint to the next

GPS’s can save many different waypoints, routes and tracklogs depending on the make and model of the GPS.

Basic setup• Main menu – Setup

– System. Put gps in demo mode or normal.

– Units. Put various “units of measure” to metric

– Time. Set time and time format

– Position format. Lat & Long or UTM/UPS

Degrees-degress

Degress-minutes-minutes

Degress-minutes-seconds

17 fig Grid Reference

– Map datum WGS 84 is a worldwide datum