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GPS. Ed Lazowska Bill & Melinda Gates Chair in Computer Science & Engineering University of Washington July 2013. Smithsonian. The time it takes the signal from a satellite to reach the GPS receiver places the receiver somewhere on a sphere that ’ s a certain radius from the satellite.
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GPS Ed Lazowska Bill & Melinda Gates Chair in Computer Science & Engineering University of Washington July 2013
The time it takes the signal from a satellite to reach the GPS receiver places the receiver somewhere on a sphere that’s a certain radius from the satellite. • Multiple satellites describe multiple spheres. • Calculate the intersection of the spheres, and you know where you are. • There’s some slop, because clocks are not perfectly synchronized.
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: GPS data is crowd-sourced from zillions of cars; FM or cellular radio communicates congestion back to the GPS unit or phone. • Ideally, you’d use historical congestion data to plan a route based upon where the congestion will be, not where it is! • I’m 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? What’s my best option, given all of this?