Re:Google Nexus 4 Review
by lukeschlather on Tuesday November 13, 2012 @11:28AM
(#4778790)
The time is effectively the time to find 4 signals.
> 4, given that you're locating in 4 dimensions --- 3 spacial and 1 time.
I think your understanding is a little flawed. The time is necessary to determine the precise distance, since both you and the satellite are in motion. After the correction for that, the problem becomes locating a body in 3 dimensions based on its distance from N points. A single point gives you a sphere, and you may be located anywhere on that sphere. Two points gives you two spheres. You might be located anywhere at the intersection of those spheres (a circle.) Three points gives you three spheres. I haven't studied the geometry extensively, but Wikipedia says three spheres usually narrows it down to two points you might be at. Knowing your altitude allows you to rule out one of those two points.
> 4, given that you're locating in 4 dimensions --- 3 spacial and 1 time.
I think your understanding is a little flawed. The time is necessary to determine the precise distance, since both you and the satellite are in motion. After the correction for that, the problem becomes locating a body in 3 dimensions based on its distance from N points. A single point gives you a sphere, and you may be located anywhere on that sphere. Two points gives you two spheres. You might be located anywhere at the intersection of those spheres (a circle.) Three points gives you three spheres. I haven't studied the geometry extensively, but Wikipedia says three spheres usually narrows it down to two points you might be at. Knowing your altitude allows you to rule out one of those two points.
https://en.wikipedia.org/wiki/GPS#Basic_concept_of_GPS