How GPS Works [MakeUseOf Explains]
As an avid gamer, I’m surprised by the correlation between GPS-like features in modern video games and the proliferation of GPS technology in mundane life. When I was a kid, paper maps and cartography were still common; if you got lost, you suffered through it and found your way to your destination. Nowadays, we’ve got the wonders of GPS to guide us there and back again.
I’m only 24 so I don’t mean to sound like the pre-GPS era was a “golden age” or anything like that. I appreciate the convenience of GPS and it has saved my butt on more than a dozen occasions. But like a lot of technology, we tend to take it for granted. I know I do.
What is GPS? Do you know how GPS works? What’s the secret behind the near-pinpoint accuracy that it offers? Keep reading to learn about the impressive thought that went into building this magnificent navigational system.
What is the common point between nuclear power, the Internet , and GPS? They all started as projects meant to bolster the US’s technological edge over the rest of the world. Specifically, the technological edge of their military. The Internet would allow fast communication over long distances; nuclear power could be both destructive and energy generative; and GPS meant ease of navigation for military forces through foreign terrain.
The GPS, which stands for global positioning system, is actually a network of 27 man-made satellites that orbit around Earth. Out of those 27 satellites, 24 are currently in use and the remaining three are there as failsafes in case one of the 24 malfunctions. Based on the arrangement of these satellites, at least four of these satellites are visible in the sky at any given time.
In tandem with the orbiting satellites, there are five monitoring stations on the Earth’s surface: the master station (in Colorado) and four unmanned stations placed in faraway locations that are as close to the equator as possible (Hawaii is one of those locations). These unmanned stations collect data from the satellites and forward to the master station, which interprets and makes adjustments before relaying the proper data back to the GPS satellites.
Though this system was originally intended for military use, the US opened up the system in 1983 for civilian use which is why we can use those satellites today to find our nearest Starbucks at the snap of our fingers.
Okay, so we have this global system of satellites and stations that are constantly shifting around in the Earth’s atmosphere and relaying data back and forth. How do our mobile devices and car trackers tap into the system to figure out where exactly we are? And if there are so many satellites floating around up there, why does your GPS signal sometimes fail ?
Think about what you use for GPS navigation. Whether it’s a dashboard mount from TomTom or the Maps app from Google , the idea is the same: your device is a GPS receiver. In other words, your device receives data from the GPS satellites overhead. What sort of data? Simply put, each satellite tells your device the distance between you and that satellite.
At this point, you may be a little confused because you’d think you need more than distance from an object to pinpoint your exact location. And you’d be right! Using the distance from each satellite, your GPS device can use a technique called trileration to find where you are.
Imagine you’re lost out in the wilderness. If you called your friend in Philadelphia and he magically knew exactly how far away from him you were, he’d tell you that you’re 400 miles from Philadelphia. Knowing that isn’t enough, though, because that distance from a single point could mean any point along the circle of a 400-mile radius around that point.
So you call a second friend in New York City and he says you’re 300 miles away. Now you have two circles of distance and every point along those circles is a potential place where you could be at this moment. As you can see, the two circles intersect in two spots: based on the distance data, you know you are at either one of these spots.
And if you called a third friend and he told you that you were 200 miles from Newark, you’d have three circles that intersect in one location. That’s where you are.
This same technique is used by the GPS where each satellite can be viewed as one of your friends from the example above. But since satellites work in 3D space, you’d have to imagine the intersection of spheres instead of circles. Combine that distance data with the fact that you must be standing on the surface of the Earth (which acts as the 4th sphere) and it’s pretty easy to find where you are.
For accurate GPS data, most devices try connecting to at least four satellites. This is also why it sometimes takes a long time for your device to update GPS locations. It’s also why you sometimes don’t have a signal: you may be connected to one or two satellites, but that isn’t enough.
Of course, there’s a lot more math and science behind how GPS works. For example, compensating for the signal delay between satellites and receivers (radio waves only move so fast). Ever wondered why GPS kills your phone’s battery ? It’s because your phone needs to constantly correct errors in calculation.
Hopefully you learned a bit about the GPS and how it works. I actually didn’t know how it all worked until I did my research for this article and the idea behind it is both fascinating and clever. If you still don’t understand it, perhaps I didn’t explain it well enough; in that case, I urge you to ask questions in the comments for clarification.
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