TGA Services » The 3D System in Depth

Over the past 20 years there has been considerable development in the 3D analysis systems measuring human kinematics. These systems fall into two categories: active or passive marker systems.

For these systems to accurately measure movement within the golf swing it is necessary to accurately measure both the body's linear movement along the three axes (XYZ) as well as its orientation (rotation), often around these axes.

These six parameters (three translations and three rotations) are known as degrees of freedom (DOF) of movement.

Highly accurate passive marker systems such as VICON, Motion Analysis Corporation and Taylormade's MATT system are based around the tracking of retro-reflective (passive) markers attached to body landmarks, by multiple high speed cameras. Given the number of cameras required (4-10), the inability of the system to work in strong sunlight and the calibration required, these systems are usually permanently based in a laboratory. The major benefits of these systems are that the golfer is free to move within the calibrated volume and no wires are attached. However 'real time' 3D movement analysis is not possible as it would take around 20 minutes or more per swing to process the results depending whether three or six DOF results are required. 'Real time' biofeedback with the golfer is not available with these systems.

Active marker systems rely on transducers of some form being attached to the body. The sensors used are relatively small, as over the past 15 years, technological advancements have much reduced their size and greatly increased their accuracy. A transmitter emits a weak magnetic field which is disturbed by the sensors that are attached to various parts of the body (head, torso, pelvis, hands, etc.). The system then tracks all movement within this field creating a precise model of the golfer and provides highly accurate data. These systems are therefore not restricted by use in strong sunlight, positioning of cameras or having to be laboratory sited. Such systems can be wireless or tethered and offer results in 'real time', allowing biofeedback work to be performed, with the obvious benefits in developing improved performance in a much reduced timescale.

The system used by Total Golf Analysis uses Polhemus hardware and, given the accuracy of data required, we use a tethered system where wires are attached to sensors that are placed on specific areas of the body. This allows us to provide results that are accurate to 1 degree and 1 mm and allows us to measure results in all six DOF, which is obviously very important when analysing a motion as precise and as fast as a golf swing. Polhemus does supply a wireless system that is capable of providing results analysing motion in six degrees of freedom, but at present it does not provide results with the accuracy required to meet our demands. I feel sure that, in time, they will develop a wireless system to suit our needs and, providing it is not prohibitively expensive, I am sure that we will migrate to it. The only downside to the Polhemus system is that large metal objects closer than 25 cm from a sensor can distort the readings and the system is wired. We feel that these limitations are a minor trade-off to the fact that there are no restrictions in swinging while tethered; the system is fully portable with short set-up times; results are in 'real time', allowing biofeedback; the system can be used in all weather conditions; and resulting data is very accurate.

There are other active marker systems that have appeared in the golf analysis industry over the last few years, most notably K-VEST and I-CLUB. These systems are wireless and therefore benefit from ease of use and are very well presented and allow biofeedback. However, both systems provide results measuring only three degrees of freedom. This means that they provide data with regard to the rotational components of the swing but do not measure the linear values of these rotations. Put simply, they do not measure the direction of the rotations as would be necessary with a golfer with excessive sway in torso or pelvis, excessive head lift or drop, loss of spinal angle, etc. This is a vital requirement when analysing golf swings and performing meaningful biofeedback. These systems, according to the makers of the transducers (Intersense who supply transducers for the K-VEST), are highly accurate, but their accuracy is limited beyond 1200 degrees per second. This makes them accurate for the large muscle groups but not so for forearms, hands and club.

To our knowledge, we are the only company offering 3D golf analysis using a fully portable system quantifying results in full six degrees of freedom and able to perform biofeedback on our students in the UK.