上次您使用手机让Google 地图(Google Maps pinpoint your exact location)在地图上精确定位您的确切位置时，您是否曾经停下来想知道GPS是如何如此准确地工作的？
全球定位系统(Global Positioning System)（GPS）系统实际上是由美国(U.S. Department)国防部于 1973 年推出(Defense)的（称为NAVSTAR）。到 1993 年，有 24颗GPS卫星围绕地球运行，并广播了军方可用于导航和其他军事目的的轨道和位置数据。今天，截至撰写本文时，已有 28 个。
在 1980 年代，从GPS卫星传输的数据向公众开放，这为我们今天拥有 的各种GPS导航设备打开了一个完整的市场。(GPS)
在撰写本文时，俄罗斯(Russia)、中国(China)、欧洲(Europe)和印度(India)都有自己的主动GPS系统。日本(Japan)正在开发自己的GPS系统，计划于 2023 年投入使用。
GPS如何工作？(How Does GPS Work?)
虽然GPS所基于的卫星技术非常先进，但系统的运行方式却非常简单。
任何单独的GPS导航系统都包含三个组件。
- 卫星(Satellites)：GPS卫星绕地球(Earth)运行，并将其当前时间和轨道位置传输到地球一侧的所有GPS接收器。(GPS)
- 指挥中心(Command Center)：指挥中心将轨道数据、时间校正和其他卫星的轨道位置传送到在轨卫星。
- GPS 接收器(GPS Receivers)：地球上的(Earth)GPS接收器接收范围内尽可能多的卫星的轨道时间，并根据至少四颗GPS卫星的位置计算自己在地球上的位置。(Earth)
GPS接收器利用称为三角测量的数学原理来计算自己的位置。
GPS三角测量如何工作(How Does GPS Triangulation Work)
从地球上的任何地方，如果你拿着一个GPS接收器（就像你手机里的那个），一个GPS接收器会从头顶上的每个GPS卫星上的同步时钟接收时间戳。
利用时间戳的差异以及无线电波传播的恒定光速，GPS接收器可以确定您所在位置与每颗卫星之间的距离。
这为GPS接收器提供了以卫星为中心的球体半径，以及您在球体边缘的位置。
由于每颗卫星都在地球上空的可预测轨道上运行，因此接收器可以使用存储的所有GPS卫星当前已知位置的历书来确定这些卫星当前在地球上空的大致位置。
借助每颗卫星的已知位置以及这些卫星与您所在位置之间的测量距离，您的GPS接收器能够通过确定这三个球体在地球(Earth)表面的交点位置来计算您的大致位置。
然后，接收器会在地图上向您显示该位置。
三颗卫星提供大致位置，GPS接收器需要来自另一颗GPS卫星的第四个信号，以使用另一种称为三边测量的数学原理来确定您当前在地球表面的高度。
您的手机 GPS 传感器如何工作(How Your Phone GPS Sensor Works)
当今大多数现代智能手机都配备了GPS接收器芯片。该芯片可以接收来自GPS卫星的无线电信号。
您手机的时钟不是原子钟，因此它的时间不会与轨道上卫星的原子钟同步。但是，在使用来自这些卫星的信号计算位置时，这并不重要。
这是因为您手机的GPS接收器专注于从卫星接收到的数据，以及地球(Earth)上已知卫星位置的数据库。由于所有卫星都有原子钟，因此每颗卫星上的当前时间在任何给定时刻都完全相同。
然而，由于与卫星的距离以及无线电信号以光速传播的事实，每个接收到的时间戳之间的差异揭示了您的手机与每个卫星之间的距离。
以下是这个 GPS 过程的工作原理：
- 所有四颗卫星都会在下午 5:12:14 向您的手机发送相同的确切时间戳。
- 您的手机在 5:12:15 从卫星 1 收到该时间戳。
- 它在 5:12:16 从卫星 2 接收时间戳。
- 最后，在 5:12:17，它接收到来自卫星 3 的时间戳。
这告诉您的GPS接收器，无线电信号从卫星 1 到达它需要 1 秒，从卫星 2 到达它需要 2 秒，从卫星 3 到达它需要 3 秒。
光速是一个已知的常数，即每秒 299,792,458 米。
使用简单的数学，接收器可以计算出它与卫星 1 的距离约为 30 万米，距卫星 2 的距离约为 60 万米，距卫星 3 的距离约为 90 万米。
使用GPS卫星数据库中的查找表，您手机的GPS接收器可以知道所有三颗卫星在地球上的大致当前位置，并提供所有三颗卫星的经度和纬度坐标。
有了这些信息，您的手机就可以计算出您自己在地球上的经纬度坐标。(your own longitude and latitude coordinates)
使用您已知的坐标，您的GPS接收器可以使用测量到的自身与第四颗卫星之间的距离来确定您所在的地球上方的高度。(Earth)
什么是辅助全球定位系统？(What Is An Assisted Global Positioning System?)
在智能手机开始集成GPS电路之前，人们通常会使用使用AA 电池的手持GPS接收器。(GPS)或者他们会在汽车上安装GPS装置，这些装置与手机的电池相连。
这是因为无线电通信需要更多功率。这样做的局限性在于，您经常需要等待几分钟，让GPS接收器“锁定”足够多的GPS卫星来计算您的位置。
智能手机制造商通过结合其现有的蜂窝三角测量技术解决了这种电池限制。早(Long)在手机启用GPS之前，它们就可以使用来自手机信号塔的信号来三角测量您的位置，使用与(GPS)GPS卫星 相同的三角测量时间戳和距离技术。
不幸的是，由于手机信号塔位于地面，这种导航计算的准确性要低得多。因此，您的智能手机GPS软件将首先使用蜂窝信号三角测量来确定您的大致位置，然后在卫星GPS数据准备好后更新该位置。
这允许现代智能手机仅在需要更新这些位置时才使用GPS数据来保留电池电量。(GPS)这就是为什么当有更准确的数据可用时，您可能会经常看到您(see your location)在Google 地图上的位置偶尔会跳转到新位置。(Google Maps)
HDG Explains : How Does GPS Work?
The last tіme you used your phone to have Google Maps pinpoint your exact location on a map, did you ever stop and wonder how does GPS work so accurately?
The Global Positioning System (GPS) system was actually launched by the U.S. Department of Defense in 1973 (known as NAVSTAR). By 1993, there were 24 GPS satellites orbiting the Earth and broadcasting orbital and positional data that the military could use for navigational and other military purposes. Today, as of this writing, there are 28.
In the 1980s, data transmitted from GPS satellites were opened up to the public, which opened up an entire market for the wide assortment of GPS navigation devices we have today.
As of the writing of this article, Russia, China, Europe, and India all have their own active GPS systems. Japan is developing its own GPS system slated to be operational in 2023.
How Does GPS Work?
While the satellite technology GPS is based on is very advanced, the way the system operates is impressively simple.
There are three components to any individual GPS navigational system.
- Satellites: GPS satellites orbit the Earth and transmit their current time and orbital position to all GPS receivers on their side of the planet.
- Command Center: The command center transmits orbital data, time corrections, and the orbital position of other satellites up to the satellites in orbit.
- GPS Receivers: A GPS receiver on Earth receives orbital times from as many satellites within range, and calculates its own position on Earth based on the positions of at least four GPS satellites.
GPS receivers utilize a mathematical principle known as triangulation to calculate its own location.
How Does GPS Triangulation Work
From any point on the planet, if you’re holding a GPS receiver (like the one in your phone), a GPS receiver receives time stamps from the synchronized clocks on each of the GPS satellites overhead.
Using the differences in timestamps, and the constant speed of light at which radio waves travel, the GPS receiver can determine the distance between where you’re standing to each satellite.
This provides the GPS receiver with the radius of the spheres with the satellites at the center, and your location at the edge of the sphere.
Since each satellite travels in a predictable orbit over the earth, the receiver can use a stored almanac of the current known position of all GPS satellites to determine where, approximately, those satellites are currently located over the earth.
With the known position of each satellite, and the measured distance between those satellites and your position, your GPS receive is able to calculate your approximate location by determining where the intersection of those three spheres come together on the surface of the Earth.
The receiver then displays that location to you on a map.
Three satellites provide a rough location, and GPS receivers require a fourth signal from another GPS satellite to determine your current altitude on the Earth’s surface using another mathematical principle known as trilateration.
How Your Phone GPS Sensor Works
Most modern smartphones today come equipped with a GPS receiver chip. This chip can receive the radio signals from GPS satellites.
Your phone’s clock is not an atomic clock, so its time isn’t synced with the atomic clocks of the satellites in orbit. However, this doesn’t matter when it comes to calculating location using signals from those satellites.
This is because your phone’s GPS receiver is focusing on the data it receives from the satellites, and a database of known satellite locations over the Earth. Since all of the satellites do have an atomic clock, the current time on each satellite is exactly the same at any given moment.
However, due to distance from the satellite, and the fact that the radio signals travel at the speed of light, the differences between each received timestamp reveals the distance between your phone and each of the satellites.
Here’s how this GPS process works:
- All four satellites transmit the same exact timestamp to your phone at 5:12:14 PM.
- Your phone receives that timestamp at 5:12:15 from satellite 1.
- It receives the timestamp at 5:12:16 from satellite 2.
- Finally, at 5:12:17, it receives the timestamp from satellite 3.
This tells your GPS receiver that it took 1 second for the radio signal to reach it from satellite 1, 2 seconds from satellite 2, and 3 seconds from satellite 3.
The speed of light is a known constant of 299,792,458 meters per second.
Using simple math, the receiver can calculate that its distance is roughly 300 thousand meters from satellite 1, 600 thousand meters from satellite 2, and 900 thousand meters from satellite 3.
Using a lookup table from a GPS satellite database, your phone’s GPS receiver knows the approximate current location over the earth of all three satellites, which provides longitude and latitude coordinates of all three.
With that information, your phone is able to calculate your own longitude and latitude coordinates on the Earth.
Using your known coordinates, your GPS receiver can then use the distance measured between itself and a fourth satellite to determine what altitude above the Earth you’re located.
What Is An Assisted Global Positioning System?
Before smartphones started integrating GPS circuitry, people typically would use handheld GPS receivers that ran off AA batteries. Or they would install GPS units in cars, which ran connected to the phone’s battery.
This was because radio communication requires more power. The limitation of this is that you often had to wait several minutes for your GPS receiver to “lock onto” enough GPS satellites to calculate your position.
Smartphone manufacturers got around this battery limitation by combining its existing technology of cellular triangulation. Long before phones were GPS enabled, they could use signals coming from cellphone towers to triangulate your position, using the same sort of triangulation timestamp and distance technology as with GPS satellites.
Unfortunately, because cell phone towers are at ground level, this navigational calculation is far less accurate. So your smartphone GPS software will first use cell signal triangulation to determine your approximate position, and then update that position once satellite GPS data is ready.
This allows modern smartphones to reserve battery power by only using GPS data when those location updates are required. This is why you may often see your location on Google Maps occasionally jump to a new location when more accurate data is available.
