Can you improve GPS accuracy with a more expensive GPS?

Q. Hi Mike, I like your site. I need a GPS to obtain OS grid refs as accurately as possible to record exact points in UK where I am making geological observations. Looks like the Garmin Etrex 10 will give me reasonably accurate readings for this purpose (+/- 25m you say). Is there any advantage as far as accuracy is concerned going further upmarket or is the accuracy obtainable more limited by the GPS system itself?

Hugh Roper, Munich, Germany

A. Hugh, Single-hand held GPS receivers will indeed only deliver the accuracy described. This level of accuracy is a result of fluctuations in the atmosphere; the signal is constantly being distorted in the stratosphere. However if you need survey-grade accuracies, for example in the range of a few centimetres, this can be done but with 'Differential' GPS. This works by having two receivers, one of which is located at a known point, such as a triangulation pillar as a base, and a second rover device which you carry to your sites of interest. The base station collects GPS data and, because its position is already known, is able to work out a positional correction which is broadcasts as a distance and angle every second. This correction is received by the rover, and the positional correction made. In the UK, the Ordnance Survey has a network of known stations around the country, and the corrections are broadcast via a mobile phone signal. This means that we users just need a rover, and a means to connect to a mobile signal. The system is called SmartNet. If you need survey locations to this level of accuracy, then send me an e-mail and I can arrange it.

Peter Hopkin, Exeter

A. No - a more expensive GPS simply has extra features like OS mapping or a larger memory to store more waypoints, routes and tracks. The accuracy of the GPS itself is limited by the GPS system. I use a Garmin Etrex 10 myself and find it accurate to with +/- 25m (and often to within +/- 3m).

Hope this helps . . .

Mike (Editor)

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