What is GPS

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What is GPS
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What is the Global Positioning System?
http//www.colorado.edu/geography/gcraft/notes/gps
/gps_f.html

• Department of Defense developed, worldwide,
  satellite-based radio navigation system
• Consists of 24 operational satellites
• Provides specially coded satellite signals that
  can be processed in a GPS receiver, enabling the
  receiver to compute position, velocity and time
• Four GPS satellite signals are used to compute
  positions in three dimensions and the time offset
  in the receiver clock

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The GPS constellation
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Satellites

• Each GPS satellite orbits the Earth twice a day
• Each satellite transmits signals to Earth
• GPS receivers measure the time between when
  satellites sent a signal relative to the GPS
  receiver receiving the signal
• Tells how far away the satellite is
• Signals from several satellites will give
  accurate results

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How do we locate ourselves in 2D space
(Trilateration)
1 point of reference 625 miles from Boise
Source http//electronics.howstuffworks.com/gps.
htm
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Increasing accuracy
2 points of reference 625 miles from Boise 690
miles from Minneapolis
Source http//electronics.howstuffworks.com/gps.
htm
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Finding the location
3 points of reference 625 miles from Boise 690
miles from Minneapolis 615 miles from Tuscon
Source http//electronics.howstuffworks.com/gps.
htm
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How do we locate ourselves in 3D space using GPS

• Trilateration in 3 dimensions

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GPS Position 1 satellite
Source After Lusch 1996
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GPS position 2 satellites
Source Garmin GPS Guide for Beginners
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GPS position 3 satellites
Source Garmin GPS Guide for Beginners
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GPS accuracy

• WAAS
• Wide area augmentation system
• Consists of 25 ground reference stations
  positioned across the United States that monitor
  GPS satellite data
• Only available in the USA
• EGNOS now in Europe
• MSAS now in Japan
• BEIDOU now in China
• GAGAN now in India
• Gives accuracy to within 5 ft

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The Geographic Grid
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(No Transcript)
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How latitude and longitude are measured
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Moving over the grid
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eTrex Venture/Legend GPS
Zoom buttons
Page button Scrolls between different screens
Find button
on/off
enter
Thumb stick