What is the accuracy of GNSS location data?
There is no unambiguous and precise answer to the question how accurate the location data provided by GNSSs is. Uncertainty is generated by distortions caused by various atmospheric strata and challenges arising from the operating environment, among others. In other words, the accuracy of location data is affected by many different factors, only some of which can be influenced by the user.
GNSS system operators publish performance data for the systems to varying degrees, which makes it difficult to compare them. The performance data provided on the European system is fairly transparent and detailed, whereas information on other systems is somewhat more vague. Indicatively, the basic accuracy of the location data provided by the various GNSSs can be estimated to be:
- Galileo (EU): 1.5 – 2 metres
- GPS (USA): 2 – 4 metres
- GLONASS (Russia) 3 – 5 metres
- BeiDou (China) 1.5 – 10 metres
The above estimates on accuracy can be considered as the baseline at which each GNSS transmits the location data towards the end user. On the way to the end user, the data encounters various factors that add a dose of uncertainty, weakening the accuracy of the location data seen by the end user. In many cases, the accuracy of the location data experienced by the user is significantly lower than the basic accuracy of the system.
Factors causing uncertainty in GNSS location data
Accuracy of location data experienced by the user
If we return to the initial question and think about the accuracy of the location data provided by GNSSs, it is difficult to give an unambiguous one-digit response. Although the internal uncertainties of the GNSS in itself are reasonably easy to manage, many uncertainties beyond the system operator's control affect the accuracy of the location information experienced by the end user.
The reported performance capabilities of the GNSSs indicate the basic level of accuracy of the service provided that the user could achieve when the uncertainties external to the system are minimized.
The accuracy experienced by the end user consists of the basic accuracy of GNSSs, to which the distortions caused by external uncertainties are added layer by layer. Some uncertainties, such as the quality of the receiver used, the users can influence by their own choices. The opportunities for the end users to influence their operating environment or other external factors are often weak.
Therefore, the answer to the question about the accuracy of location data could be: “the GNSSs produce the necessary initial data for determining location data with an accuracy of 1 – 2 metres, but in city centres the location data computed by the mobile phone may vary between 5 to 30 metres”.
If the end users desire location data of uniform quality, they must also use careful consideration when selecting terminal equipment and planning their use. The GNSS administrator cannot correct the poor choices made by the user. If the operating environment of the end user causes too many uncontrolled uncertainties, other methods can be used to support GNSSs in the provision of location data.
More information: gnss(at)traficom.fi