Time to Find Your Way
All scenes › Chapter 2 Three Strings
One in space, one on the ground
Throw out the point in space; the one on the ground is you
View in 3DOne in space, one on the ground
One of the two points is on the ground, and the other is about 24,900 km up in space. A car can’t be in space. So the phone picks the point on the ground. That’s where you are right now. And this way of finding a position with several strings is actually very old.
Why?The point in space is far from Earth’s surface, so it’s easy to throw out. The phone does its math knowing you’re somewhere near the surface.
Learn moreReal phones use four or more satellites, not three. We’ll see why the fourth one is needed in the next chapter. The reason is the star of this story: time.
- The point where the three spheres meet on the ground
- You are here
textbook formulas
View this scene in 3D →More in the series
Orbits, distances and clock differences are calculated with textbook formulas (Kepler’s laws and simple forms of special and general relativity). The 30 satellites follow the real GPS layout but are not the real satellites or positions. In the 3D view, the satellite models are drawn huge and radio waves move far slower than in real life.