Standalone GPS may be inadequate for many applications in terms of its integrity, accuracy, continuity and availability, and as a result many augmentation methods can be employed to assist the standalone GPS. Some of these include through receiver algorithms, coupling with additional sensors, extra Global Navigation Satellite Systems, GPS modernization, and various space-based and ground-based augmentation systems.
Some of these can be applied to GPS devices used in sport, but others aren’t due to the fact that it is may be too costly to implement certain augmentation methods, or the processing necessary to achieve a better accuracy in position is not required.
An accelerometer is an electromechanical device capable of measuring acceleration forces acting on an object, with these forces being static or dynamic (Dimension Engineering, 2008). An example of a static force is the constant pull of gravity downwards, and a dynamic force is caused by movement or vibration of the device.
By measuring the amount of dynamic acceleration, a user is able to analyse the way that the device is moving (Dimension Engineering, 2008).By undertaking a few calculations, speed of the unit can be calculated, and hence distance can be derived as well. Triaxial accelerometers are intended to measure simultaneous movement in the three perpendicular axes. Total acceleration will be the sum of the dynamic acceleration in the three directions.
For these reasons, tri-axial accelerometers have been used to determine human behaviour and identify periods of movement (Mathie et al., 2003). Furthermore, Mathie et al. (2003) mentions that these movements require a high sensitivity device for accurate determination of results. By combining accelerometers with GPS, not only can movement be determined accurately, but position can be applied for the ability to track the objects movements. For these reasons, GPS coupled with accelerometers can be used as a useful tool in sports to determine player’s movements and statistics.
The SPI Elite device used in data collection for this thesis not only houses the GPS unit itself, but in addition is coupled with a tri-axial accelerometer, and a data logger capable of collecting 14,000 observations (which translates to approximately four hours of data records captured at one second intervals, but is claimed to log seven plus hours). These observations can then be downloaded via USB to the computer, and analysed using the software available. GPSports (2007) claim that “the SPI Elite distance and speed results have been recently validated with less than a 1% error in true outputs”.
Figure 3 The SPI Elite unit, housing the GPS unit, tri-axial accelerometer and containing a data logger (GPSports, 2007)