Andrew McLean Kelvin Barraclough Gisborne Secondary College
What is GPS? 24 + satellites
What is GPS? 24 + satellites Several ground stations
What is GPS? 24 + satellites Several ground stations GPS receiver
Satellites Altitude ≈ km
Satellites Altitude ≈ km Period 12 hours
Satellites Altitude ≈ km Period 12 hours At least 4 visible everywhere
Satellites Altitude ≈ km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter
Satellites Altitude ≈ km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter Transmit on MHz
Satellites Altitude ≈ km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter Transmit on MHz Fitted with atomic clocks
Satellites Altitude ≈ km Period 12 hours At least 4 visible everywhere Solar powered, ≈ 50 W transmitter Transmit on MHz Fitted with atomic clocks Lifespan ≈ 10 years
Ground Stations I master station, four remote
Ground Stations I master station, four remote Monitor satellites and send back accurate orbital and time data
The Signal The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS.
The Signal The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. The “ephemeris”. Accurate data of individual satellite position.
The Signal The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. The “ephemeris”. Accurate data of individual satellite position. The “pseudo random code”. Effectively, an accurate time signal
The Signal The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. The “ephemeris”. Accurate data of individual satellite position. The “pseudo random code”. Effectively, an accurate time signal Turned off while satellite orbit is adjusted
Satellite positions km km
Signal times s s
Establishing position
If receiver had a good enough clock – Two satellites – somewhere on a circle
Establishing position If receiver had a good enough clock – Two satellites – somewhere on a circle 3 rd satellite – cuts this circle twice, but usually one solution is obvious
Establishing position If receiver had a good enough clock – Two satellites – somewhere on a circle 3 rd satellite – cuts this circle twice, but usually one solution is obvious 4 th satellite – removes ambiguity
Establishing position With a small, cheap clock -
Establishing position With a small, cheap clock – 3 satellites give 2D fix
Establishing position With a small, cheap clock – 3 satellites give 2D fix 4 satellites give 3D fix
Accuracy Given clear view of sky typically 5 – 10 m
Receivers Aren’t equal
Receivers Aren’t equal Need “good view” of sky
Possible information Position
Possible information Position Distance travelled
Possible information Position Distance travelled Speed
Possible information Position Distance travelled Speed Direction
Possible information Position Distance travelled Speed Direction Altitude
Gathering data – “low tech”
Gathering data – “hi tech” Almost all GPS receivers can be connected to a computer to transfer data
Suitable software (1) “OziExplorer”
Suitable software (1) “OziExplorer” $130
Suitable software (1) “OziExplorer” $130 Uses raster mapping
Suitable software (1) “OziExplorer” $130 Uses raster mapping Suitable for all brands of GPS
Suitable software (1) “OziExplorer” $130 Uses raster mapping Suitable for all brands of GPS Transferring data from Ozi is awkward
Suitable software (2) Garmin “Mapsource”
Suitable software (2) Garmin “Mapsource” Free with Garmin GPS
Suitable software (2) Garmin “Mapsource” Free with Garmin GPS Uses Vector mapping
Suitable software (2) Garmin “Mapsource” Free with Garmin GPS Uses Vector mapping Allows easy transfer of data to other programs (eg Excel)
Some possibilities Real aircraft - loop the loop Model aircraft Racing cars, dragsters, motorbikes Skydivers, bungee jumpers Yacht racing Theme park rides Relative motion on moving ship
Cost? Cheap GPS ≈ $100 Garmin GPS Map 60 CSx ≈ $470 OziExplorer $130 Oztopo maps for Garmin (all of Australia) $229