How Does My Navigation System Know Where I Am?

“Take a left, then a right, keep going until you see McDonalds on your left…. No wait – take the left instead of the right!” If you’ve ever had the pleasure of having to make sense of this confusing dialogue or indeed if you’ve ever baffled some unsuspecting driver yourself with directions then you’ll know how difficult it can be. The widespread adoption of navigation systems have more or less eliminated this problem and now, a simple postcode or address is all that’s needed to get to where you want to go. But how do these navigation systems know where you are? I doubt they have someone on the other end giving them directions (like the ones above)!

GPS (Global Positioning System)

The vast majority of devices use a US created system called Global Positioning system or GPS. GPS is a collection of 27 satellites orbiting the Earth in a sequence. 24 of the 27 satellites are currently in use and the remaining 3 are used for backup. The satellites have carefully positioned so that four satellites are able to see a certain point at any given time. GPS can function properly with the use of just three satellites at any given time but uses 4 for additional accuracy.


There are a few other set of satellites competing with GPS such as Galileo and Beidou but the most promising competitor is GLONASS which has a total of 24 satellites – of these 24, three are used for backup purposes. GLONASS has better accuracy than GPS due to its satellites being positioned better than those used by GPS. Many GLONASS satellites were un-operational before but now that GLONASS has got to a stage where it can be used by the masses, it is quite possible, the Russian created satellites will topple GPS in the near future due it being able to provide greater accuracy than GPS! It is already being implemented as an additional set of satellites to improve accuracy in some newer devices – the Garmin Glo, new Sony Xperia devices and even the iPhone 4S and iPhone 5 have introduced GLONASS support in addition to GPS.

GLONASS Satellite

GLONASS Satellite – Operated by the Russians

Calculating the Distances From You and the Satellite

Each satellite continuously broadcasts a signal consisting of a long string of randomly generated data. The amount of time taken for the signals to be sent and received from the navigation system to the satellites shows how far the navigation system is from each of the four satellites. While this information is useful in determining the distance from the navigation system to the satellites, it isn’t enough since the navigation system only knows the distance from various satellites, it doesn’t yet know in which direction it is from the satellites. To determine this, your navigation system uses Trilateration!


Navigation systems use Trilateration to determine where you are. This process sounds complicated but the basic concept is actually quite simple. If you know how far you are from three different locations, you can pinpoint exactly where you are. Consider the following scenario: You get lost and ask for directions. You are told you are 100 miles from location A. This doesn’t tell you where you are but at least you know you are within a 100 mile radius of location A. Next you see a sign that says you are 150 miles away from location B. You now know you are within a 100 mile radius of location A and a 150 mile radius of location B therefore you must be somewhere where the radius of location A and location B intersect. Luckily another person passes by who tells you, you are 200 miles away from location C. You can now use the distances between each of these three location to determine where you are since you will be at the point where the radius all three of these locations intersect. Still confused?

The below video presentation explains this a little better:

BIO: Rashed has an MSc in Software Engineering and enjoys guest posting on technology related topics. After learning about the GLONASS technology, Rashed did some research into hw navigation systems work and wanted to share this information with the readers of VB. This is a guest post on behalf of vehicle tracking experts RAM.

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