十万个为什么·科学启蒙30篇（2）

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GPS设备如何知道你的精确位置？

GPS devices receive signals from at least four satellites orbiting Earth at 20,000 kilometers high.
Each signal carries precise time data from atomic clocks aboard the satellites.
The device calculates distance to each satellite by measuring how long the signal took to arrive.
Using trilateration, it pinpoints your location where three imaginary spheres intersect.
Tiny timing errors—even one-millionth of a second—can cause position mistakes of hundreds of meters.
Ground stations constantly monitor and correct satellite orbits and clock drifts.
Your phone combines GPS with Wi-Fi and cell tower data to speed up and refine location fixes.
Atmospheric delays slow down signals, so advanced receivers apply real-time correction models.
Military GPS uses encrypted signals for higher accuracy than civilian versions.
That’s how your map app knows whether you’re on the left or right side of the street.