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Technology  
Global positioning

At present a 5 - 10 m positioning accuracy can be achieved with the vehicle module. It is important that the GPS aerial should have a direct sight to the sky. Naturally, positioning does not work in case of vehicles moving in tunnels or parking in buildings but the receiver is sensitive enough to position accurately in narrow streets enclosed by high buildings.

INTRODUCTION

Positioning is based on satellite reference transmitters. These satellites are orbiting at a height of 20 kms. In order to have at least 4 satellites in view from all points of the globe with the required gradient (using satellites located close to the horison causes inaccuracy), at least 24 satellites have to be kept in work (there are more than this number).

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GPS satellites orbiting the Earth. Black dots are the satellites (along with their number) theoretically visible from a certain point of the surface (blue dot).
Source: Wikipedia

The device measures its distance with the built-in GPS receiver from at least 4 satellites. The intersection of the measured distances defines an obvious spatial position (distance from 3 satellites would give two intersections). Generally, the more satellites can be seen, the more accurate the measurement is. The positioning is spatial, 3 dimensional, that is, gives altitude data in addition to the horizontal position. The GPS receiver in itself is a passive device not communicating with the satellite, it only calculates coordinates. The further intelligence of all GPS-based systems is determined by the way how these coordinates are used, where they are transferred to and how it is able to satisfy user requirements.

The device calculates one position data in each second. In order to reduce the amount of data, the device is able to perform a stop-detection, that is, it senses the lack of significant change in position data from second to second, and stores them more rarely. An Atlas vehicle module optimalised for agricultural usage, has a so-called slow vehicle mode as well. In this case stop-detection is done with a more advanced algorithm and is able to separate wandering from the actual movement, even in the case of a deep ploughing tractor moving with only a few kmh speed.

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GPS

GPS is the abbreviation of Global Positioning System. Originally it was made for the US Department of Defence, for military purposes.


Wandering

Sometimes the GPS receiver calculates changing position of a vehicle that is standing still in reality. This virtual movement of the vehicle is caused by the movement of satellites and is called wandering. These measurements scatter within only a few meters.

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