GPS Ed Lazowska Bill & Melinda Gates Chair in Computer Science & Engineering University of Washington August 2010

Smithsonian

z 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. z Multiple satellites describe multiple spheres. z Calculate the intersection of the spheres, and you know where you are. z There’s some slop, because clocks are not perfectly synchronized.

Wikipedia

z Maps: There are several public datasets that describe all the roads as line segments. This is a huge volume of data. z Route planning: Treat the road network as a graph. z Traffic congestion: FM radio communicates congestion to the GPS unit. y Ideally, you’d use historical congestion data to plan a route based upon where the congestion will be, not where it is! x 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?