How does GPS work?

[gsmittle]

As a result the receiver solving a 4-variable, 4 unknown math problem resolves X, Y, and Z and the true time (to about 1 microsecond precision or better) …[snip]… The coordinates can then be translated to Latitude and Longtitude and elevation - e.g. cartesian coordinates to azimuth, elevation and radius relative to the center of the earth, that's just a simple 3D geometry transformation.

…[snip] ANother interesting fact is that differential measurements, e.g. nearly simultaneous at two spots are only accurate to 10 feet maybe but the distance between them that you calculate may be accurate to inches. GPS velocity, because it uses very precise measurements of time, and the difference between two consecutive measurement points, is also very, very accurate.

I won't pretend to understand this. Can I just pretend it's elves (or Elvis) in the little box?

g.

[Mr__Bill]

I have played with the GPS in my phone. One thing I notice is that when I am standing with the phone about 5' above the water (granted the water level fluctuates about 9') the GPS will tell me that I am 50+ feet above sea level with a +- of anywhere from 30 to 900 feet. It also tell me that it's using 5 to 9 out of 11 satellites. I really hope it's the phone, as I understand that airplanes are now using gps to land.....


Bill
on the left coast

[cabinetman]

I have played with the GPS in my phone. One thing I notice is that when I am standing with the phone about 5' above the water (granted the water level fluctuates about 9') the GPS will tell me that I am 50+ feet above sea level with a +- of anywhere from 30 to 900 feet. It also tell me that it's using 5 to 9 out of 11 satellites. I really hope it's the phone, as I understand that airplanes are now using gps to land.....


Bill
on the left coast

If it's a smart phone, will it tell you when to duck?

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