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How does GPS work?

TomTom Education

How does my TomTom device work?

Inside your TomTom Device

The GPS software and hardware
Put simply, your TomTom device consists of two distinct elements: the software and the hardware.

A small computer inside your device ensures the software runs smoothly. Depending on the device you’ve got, the software is to be found on either the SD card or the hard disk. The hard disk itself can store some 20GB of data.

A ‘boot loader’ in the computer searches the hard disk or SD card for the software and your map data. It then transfers the software to the 64MB internal RAM memory in your TomTom device and starts the software. Only that part of your map that’s actually needed at that moment is then loaded. When you consider that in 1991 an IBM personal computer ran on only 16MB, you realise what a powerful little device your TomTom actually is!

A Linux system in the device makes sure the hardware functions properly. The hardware itself starts the GPS and the navigation application. The navigation application then reads whatever settings you have installed, such as your preferred voice and your last chosen route.

The GPS module
The GPS module in your TomTom device makes sure that the satellite signal is translated into co-ordinates pinpointing your exact location on the map.

Once everything has been ‘started up’, the GPS module in your device calculates where you are from the satellite signals it receives. The satellites constantly send out signals and the module picks up those that are nearest to it.

As you know, the GPS module works out its position by calculating its distance from at least four different satellites. But while your TomTom device may know its distance from these satellites, it still doesn’t know exactly where you are until it also knows where the satellites are positioned. Even then it’s not straightforward, as each satellite is constantly moving in orbit around the earth.

This last problem is solved by the fact that the GPS signal the satellites send out contains so-called ‘almanac’ information. Information about such things as the altitude of the satellite, which satellite it is, its position in relation to the other satellites, and so forth. Using this information, your GPS module can translate these signals into co-ordinates, which it then sends on to the navigation application.

Which is where your GPS module really comes into its own. Inside the module is a small, highly sensitive GPS chip that can receive and register signals even when it’s in very inaccessible locations, such as down narrow alleys, amongst high buildings or in dense woods. Which obviously greatly improves the accuracy and consistency of your TomTom device.


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