Tracking estimates the camera poses in real time so that the AR
maintenance contents can be augmented to the technicians
correctly in the real environment. Three tracking approaches are
used, namely, ARToolkit for tracking predefined fiducial markers
and registering the contents created using the bi-directional tool,
PTAM (Parallel Tracking and Mapping) [10] for constructing 3D
maps online and registering the 3D animations via ONA module,
and template matching [12] for searching the rectangular region in
each frame of the live video and registering the 2D symbols on the
matched region.