GPS

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GPS

• Ed Lazowska
• Bill Melinda Gates Chair in
• Computer Science Engineering
• University of Washington
• August 2009

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(No Transcript)
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Smithsonian
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• The time it takes the signal from a satellite to
  reach the GPS receiver places the receiver
  somewhere on a sphere thats a certain radius
  from the satellite.
• Multiple satellites describe multiple spheres.
• Calculate the intersection of the spheres, and
  you know where you are.
• Theres some slop, because clocks are not
  perfectly synchronized.

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Wikipedia
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• Maps There are several public datasets that
  describe all the roads as line segments. This is
  a huge volume of data.
• Route planning Treat the road network as a
  graph.
• Traffic congestion FM radio communicates
  congestion to the GPS unit.
• Ideally, youd use historical congestion data to
  plan a route based upon where the congestion will
  be, not where it is!
• Im at Microsoft, headed for UW, at 8 a.m. An
  accident has just occurred westbound midspan on
  the 520 bridge. How long is it likely to take
  I-90 to become congested? How long is it likely
  to take Bothell Way to become congested? Whats
  my best option, given all of this?