Improbable as it may seem, the whole
idea behind GPS is to use satellites in space as reference points for locations here on
earth.
That's right, by very, very accurately measuring our distance from three satellites we
can "triangulate" our position anywhere
on earth.
Forget for a moment how our receiver measures this distance. We'll get to that later.
First consider how distance measurements from three satellites can pinpoint you in space.
The Big Idea Geometrically:
Suppose we measure our distance from a satellite and find it to be 11,000 miles.
Knowing that we're 11,000 miles from a particular satellite narrows down all the
possible locations we could be in the whole universe to the surface of a sphere that is
centered on this satellite and has a radius of 11,000 miles.
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