Pipe Solutions

Choosing the right GPS accuracy

When a project is commissioned there is often a desire or expectation for a particular positioning accuracy. It's interesting to compare a number of different systems and see what sort of results can be expected.

There are numerous factors that influence the accuracy of GPS including collection technique, satellite coverage, signal reflections from buildings, heavy tree cover, build quality of the GPS receiver, however for this discussion we will assume the GPS systems are operating in good conditions within the coverage of a GPS correction service.

GPS systems are usually quoted by their accuracies - Survey Grade (+/- 1cm), Mapping Grade (+/- 10cm) and Sub-Meter (+/- 1m) however given that there are many variables to consider with GPS we need to look at what sort of results that could consistently be achieved. When an accuracy is quoted as +/- 10cm it refers to 1 standard deviation of the mean error. In statistics an error distribution can be represented by a bell curve (see below).

What this means in real terms is that typically 68.2% of results will be within +/- 10cm, 21% will be within +/- 20cm and the remaining 10% will have a lower accuracy. This may mean that even though +/-10cm equipment is used the results obtained may not be within specifications if 0.1m accuracy is required.