We’re all used to satellite navigation systems such as GPS or GLONASS, sheer magic in which the combination of a set of reference transmitters and super-accurate timing information can be used to calculate a position to an astounding precision. They had land based predecessors such as LORAN and Decca Navigator which worked in a similar fashion but with fixed land-based reference transmitters. Terra is an attempt to do the same thing without a network of dedicated transmitters, instead using FM broadcast transmitters as its fixed points.

This might seem like an impossible task without access to the transmitters, but they have a workaround using the Internet as a backhaul. Instead of transmitting their timing information like the systems mentioned above, they rely on a set of reference receivers sharing it online to the client’s receiver software. So far they have a demo running in Denver.

The interesting thing about this system is that it’s open-source, and requires only a relatively inexpensive software defined radio receiver and a computer to operate. Now anyone with a group of internet-connected friends to set up reference receivers can have their own positioning system, it’s no longer the exclusive preserve of governments. We like this idea, and we look forward to seeing it being tested more widely.

If you’d like to know where we’ve come from, we’ve taken a look at LORAN before.

我们都已经习惯了像 GPS 或 GLONASS 这样的卫星导航系统，这是一种纯粹的魔法：通过一组参考发射器与超精准时间信息的组合，就能计算出极其精确的位置。此前也有地面定位系统，如 LORAN 和 Decca Navigator，它们的工作原理类似，但使用的是固定的地面参考发射器。Terra 项目试图在没有专用发射器网络的情况下实现同样的目标，而是使用 FM 广播发射器作为其固定参考点。

在没有访问发射器权限的情况下，这看似是一项不可能完成的任务，但他们找到了一种变通方法：利用互联网作为回传通道。与上述系统通过发射器传输时间信息不同，Terra 依靠一组参考接收器，将时间信息在线共享给客户端的接收软件。目前，他们在丹佛已经有一个演示系统在运行。

该系统的有趣之处在于它是开源的，并且只需要一台相对廉价的软件定义无线电接收器和一台计算机即可运行。现在，只要有几个人通过互联网连接起来设置参考接收器，任何人都可以拥有自己的定位系统；这不再是政府的专属领域。我们非常喜欢这个想法，并期待看到它在更广泛范围内进行测试。

如果您想了解我们是从哪里起步的，我们之前曾介绍过 LORAN 系统。