GPS Devices used by airlines or the military can provide accuracy down to the centimetre.
However, most GPS devices used in vehicle tracking or satellite navigation provide accuracy of under 2 metres.
But what does this mean.
To work out its location a GPS device will look at the signal from a number of GPS devices and work out its position in relation to them. The more satellites the device can see, the better the accuracy. Unfortunately, by the time the signal reaches the earth it is very weak, it can be affected by environmental conditions in the atmosphere or it could be blocked completely by hills, buildings or trees.
If the signal from one satellite is blocked, then in most cases the GPS device can fall back on the remaining satellites. However, if the GPS device is in a garage then this could mean the device has no signal and can therefore cannot calculate its position.
There are therefore a number of points to consider when reading a statistics which quotes GPS accuracy of 2 metres.
Firstly, when companies quote a figure of 2 metre accuracy, this actually means that 60% of the time, you will get an accuracy at or below 2 metres. As the GPS signal can be affected by a number of factors, then on average, 40% of the time the GPS accuracy could actually be greater than 2 metres. We use sophisticated software algorithms to predict where the vehicle is. WiFi, CellId and accelerometers in the device can also be used in addition to GPS to provide a location when GPS is not available.
Secondly, as GPS tracking devices transmit their location over the mobile network, if they cannot transmit through the network because they don’t have a good mobile signal then this could mean that the location is out of date and the vehicle appears to be in an old location. As soon as the unit can transmit, then the location will be corrected.
The combination of the above may therefore be an issue when determining the exact location where a vehicle stopped especially if the vehicle has parked in a garage or underground car park.
As the unit cannot get GPS or transmit its location, then this means that the location shown will be the previous location rather than the final location. ie where the vehicle was a few seconds before. In most cases this is not an issue although obviously the faster the vehicle is going, the more distance it will have travelled in those last few seconds and therefore the more innacurate the location.
Finally, in the UK we use postcodes as a reference to location. However, this actually causes an additional problem as a postcode is an area without a standard shape. It is not a point, and therefore to compare the location of a GPS device with a postcode means that additional calculations have to be done.
In order to determine a particular postcode, the Royal Mail provides the centre point of that postal area. However, as the shape of the postal area varies, this could mean that the centre point of a different postal area is actually closer to the location of the device. The GPS device might be shown in the correct location but in the wrong postal area.
This is clearly demonstrated with the two points shown in the image below. Although the GPS device may be correctly showing the location in SW3, because of the shape of the surrounding areas, it is actually closer to the mid point of the postcode area SW7.
In most cases, this is not an issue. Its pretty clear from the location of the vehicle on the map where it is or what the vehicle is doing. Additional support is provided by our activity report. At AutoAlert, we also do a lot of work in the background to ensure you can be confident in knowing where your vehicles is or what it is doing.
However, it is worth bearing in mind when considering using GPS tracking systems, that the location can be affected by various factors and like a mobile telephone it may not always have signal.
For more information about GPS tracking, check out our support centre
0207 099 5698