When tracking is not active, the system monitors an 8 by 8 pixel ``tracking trigger'' located in the lower right corner of the workspace. As each image is acquired at time k, the contents of this tracking trigger are subtracted from the contents at the previous image k-1. This creates a difference image. The energy of the difference image is used to detect the trigger. When a pointing device enters the tracking trigger, the energy rises above a threshold. In order to assure that the tracking device is adequately positioned, the system waits until the difference energy drops back below the threshold before acquiring the reference template. At that point, the contents of the tracking trigger are saved as a reference image, and the tracking process is initiated.
Tracking continues as long as the correlation remains above a relatively low threshold. However, it can happen that the tracker locks on to a pattern on the digital desk (for example a photo of the pointing device!). To cover this eventually, if the tracked location of the pointer stops moving for more than a few seconds (say 10), the system begins again to observe the difference energy in the tracking trigger. If the trigger energy rises above threshold, the tracker will break the previous track and re-initialise the reference pattern with the new contents of the tracking trigger.
When tracking is not active, the system monitors an 8 by 8 pixel ``tracking trigger'', Tk(i,j), located in the lower right corner of the workspace. As each image is acquired at time k, the contents of this tracking trigger are subtracted from the from the contents at the previous image k-1. This creates a difference image as shown in figure 5. The energy of the different image is computed as
When a pointing device enters the tracking trigger, the energy rises above a threshold. In order to assure that the tracking device is adequately positioned, the system waits until the difference energy drops back below the threshold before acquiring the reference template. At that point, the contents of the tracking trigger, Tk(m, n) are saved as a reference image, and the tracking process is initiated.
Figure 3: Temporal different of images in the reference square.
Tracking continues as long as the minimum value of SSD remains below a relatively high threshold. However, it can happen that the tracker locks on to a pattern on the digital desk (for example a photo of the pointing device!). To cover this eventuallity, if the tracked location of the pointer stops moving for more than a few seconds (say 10), the system begins again to observe the difference energy in the tracking trigger. If the trigger energy rises above threshold, the tracker will break break the previous track and re-initialise the reference pattern with the new contents of the tracking trigger.