资 源 简 介
The goal of the Global Positioning System (GPS) is to determine
your position on Earth in three dimensions: east-west,
north-south, and vertical (longitude, latitude, and altitude).
Signals from three overhead satellites provide this information.
Each satellite sends a signal that codes where the
satellite is and the time of emission of the signal. The
receiver clock times the reception of each signal, then subtracts
the emission time to determine the time lapse and
hence how far the signal has traveled (at the speed of light).
This is the distance the satellite was from you when it emitted
the signal. In effect, three spheres are constructed from
these distances, one sphere centered on each satellite. You
are located at the single point at which the three spheres
intersect.
