Why Your Phone’s GPS Needs Four Satellites—Not Just One

为何手机GPS需要四颗卫星，而非一颗

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GPS calculates position by measuring how long signals take to travel from satellites.

GPS通过测量信号从卫星传播所需的时间来计算位置。
Because light speed is constant, timing errors translate directly into distance mistakes.

由于光速恒定，计时误差会直接转化为距离误差。
Three satellites give you latitude, longitude, and altitude—but only if your clock is perfect.

三颗卫星可确定纬度、经度和海拔高度——但前提是你的时钟绝对精准。
Your phone’s internal clock isn’t accurate enough, so a fourth satellite helps correct timing drift.

手机内置时钟精度不足，因此第四颗卫星用于校正时间漂移。
This process, called trilateration, works in three dimensions, not just on a flat map.

这一过程称为三维定位（trilateration），不仅适用于平面地图。
Engineers designed the system to handle atmospheric delays and signal reflections too.

工程师在设计系统时，也考虑了大气延迟和信号反射问题。
Even tiny timing errors—just one microsecond—would misplace you by 300 meters.

哪怕只有1微秒的计时误差，也会导致300米的位置偏差。
So precision engineering, physics, and real-time computation all work together silently.

因此，精密工程、物理学与实时计算在幕后协同工作。