For the regular user, the GPS is the only mapping solution they grew to learn and trust. They never had to navigate the stars, or never had to learn to read a regular map. At some point after using these GPS receivers in our daily lives, you may have wondered exactly how these wonderful devices actually worked.
There are many factors involved in making the whole GPS system actually work. It involves a lot of math and a lot of complicated jargon that I know you have absolutely no time for. So what you’re going to learn today is the basic gist of how the GPS device in your wrist, mobile, or car can identify your current location anywhere in the world.
The first concept that you have to wrap your minds around is the fact that these GPS devices we have are basically just receivers. They receive signals from 24 man-made satellites that orbit the earth far up in the sky. These satellites are a vital ingredient in identifying exactly where you are in the world.
These 24 satellites are arranged to circle the earth in many different directions. They are arranged in such a way that at any point in the world, there should at least be a minimum of 4 satellites in view. In reality, if the world had no buildings, mountains or any other structure that hinders your view of the horizon, there should at least be 6-10 satellites in full view at any given time.
Each of these satellites is used as reference points by our GPS receivers to calculate exactly where we are in the world. To better understand how this works, let’s turn it into a little story.
Try This Out
Say you are lost and you found 4 locals who you approach to inquire about where you are. Unfortunately, they didn’t tell you exactly where, but they decided to tell you how far you are from a certain landmark.
One guy tells you that you are 9.5 Km away from Cumberland County Fairgrounds. The other guy tells you that you are at least 28 Km away from Hancock House. The third guy tells you that you are about 20 Km away from Scotland Run Park. The last guy tells you that you are at least 15 Km away from Blackwater Pond Park.
If you take a regular map and draw a circle indicating the proper distances from these landmarks, eventually you will have 4 circles that intersect at one point. Try it out to find out where you are if these were the directions given. I’ll tell you the answer later.
Landmarks in the Sky
In the same way, rather than using actual landmarks in the land, your landmarks are the satellites in the sky. Your GPS receivers figure out its distance from at least 4 satellites and arrive at an intersecting point where it can identify its location relative to these 4 satellites. More satellites in view make the location data even more accurate but 4 should suffice in most situations.
Of course, there are more data involved in this that you’d think. After all, these satellites are always moving. Fortunately, these satellites are moving at a predetermined speed and direction. By knowing exactly what time it is, the GPS satellite knows where it should be at that point in time giving the receiver an exact location to refer to in the world.
Time is actually a very important factor in GPS navigation. Not only is the time necessary to identify exactly where the point of reference will be, but it will also be necessary to figure out a GPS receiver’s distance from a Satellite.
Distance in Time
GPS satellites communicate with a receiver by emitting a radio signal in all directions. The radio signal usually has 2 important details – the time the signal was sent and the location of the satellite when the signal was sent.
When the GPS receiver intercepts a radio signal, it calculates the distance using the speed of the signal as well as the time it took for the signal to be received. Using these complex calculations, it can identify its distance from one satellite. This goes on for all satellites in view. After all the data has been collected, the receiver identifies the intersecting points to determine its location.
Well, that’s it. That is the most basic way a GPS receiver figures out where you are in terms longitude, latitude and elevation. Other added information, such as actual location in reference to a map, speed, travel time, etc. depends on the capabilities of your chosen GPS device. Each device is still unique even though they basically do the same thing when identifying your location since whatever added features they have could impact the accuracy and usefulness of the receiver.
Oh, if you are wondering where the directions point to in the earlier exercise, it is in Parvin State Park, NJ. Happy navigating!
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