Andrew McLean Kelvin Barraclough Gisborne Secondary College.
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Transcript of Andrew McLean Kelvin Barraclough Gisborne Secondary College.
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 ≈ 20200 km
Satellites
• Altitude ≈ 20200 km• Period 12 hours
Satellites
• Altitude ≈ 20200 km• Period 12 hours• At least 4 visible everywhere
Satellites
• Altitude ≈ 20200 km• Period 12 hours• At least 4 visible everywhere• Solar powered, ≈ 50 W transmitter
Satellites
• Altitude ≈ 20200 km• Period 12 hours• At least 4 visible everywhere• Solar powered, ≈ 50 W transmitter• Transmit on 1575.42 MHz
Satellites
• Altitude ≈ 20200 km• Period 12 hours• At least 4 visible everywhere• Solar powered, ≈ 50 W transmitter• Transmit on 1575.42 MHz• Fitted with atomic clocks
Satellites
• Altitude ≈ 20200 km• Period 12 hours• At least 4 visible everywhere• Solar powered, ≈ 50 W transmitter• Transmit on 1575.42 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
27400 km
20200 km
Signal times
0.091 s
0.067 s
Establishing position
Establishing position
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• 3rd 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• 3rd satellite – cuts this circle twice, but usually
one solution is obvious• 4th 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