*2.3.1 Electromagnetic-based position tracking*

The electromagnetic tracking system is one of the popular types of freehand scanning system. Similar to the optical tracking system, this system also consists of two important components: the electromagnetic sensor mounted on the probe, as well as the electromagnetic transmitter, which tracks the position and orientation of that sensor on probe [4]. The recorded spatial information is then transferred to the computer workstation for reconstruction and visualization. However, electromagnetic tracking system suffers from the interference of magnetic signals if working nearby the sources, for example, surrounding metal instruments and power cables, which will affect the tracking accuracy [12], and also caused geometric distortion during the 3D reconstruction process [1].
