This defines a working volume which encloses the tracked object. 2.1 Mechanical Arm-type tracking devices typically use potentiometers or optical encoders to measure the rotation of a joint between rigid linkages. Another type of mechanical tracking is to measure force exerted on a measuring device such as a strain gauge. Typically this second technique is used in force-sensing joysticks. Advantages Simple sensors mean that lag is low, an important factor especially when tracking head movements.
Mechanical trackers tend to be low cost.
Disadvantages Typically arm-type trackers will have a small working volume, since using the device requires the user to be tethered. As with any device that has moving parts, mechanical trackers may wear out after a period of time. An electromagnetic tracker comprises a transmitter and a receiver. A fluctuating magnetic field generated in the three orthogonal coils of the transmitter is picked up by three corresponding coils in the receiver. The variations in the received signal can be used to calculate the relative position and orientation of the receiver and transmitter with six degrees of freedom.