APAS-XP Extra Performance
Central to APAS-XP is a completely new marker tracking system for auto-digitizing the video sequences. This new auto-digitizing is called 3D Auto-Track. Internally the software calculates and saves the 3D location of each marker for each frame. Then for each point in a new frame a complex algorithm is applied to the past 3D trajectory and an expected 3D location is computed. The expected 3D location then is transformed to each camera view and the software searches for markers starting at the expected location in the different camera views. In this way the system "knows" where a marker should be in each view even when it is not visible in a view. When a marker re-appears in a view after potentially many missing frames the software will pick it up because the software has been tracking in 3D.
Additionally various image enhancement algorithms are applied to the image that aid in the rejection of incorrect marker candidates. Additional algorithms further reject extraneous markers.
Being able to track the markers in 3D is critical to the proper functioning of the algorithm. This means that each marker should be seen by at least 2 cameras at all times, however which 2 cameras may change. For this reason we recommend using 5 well spaced cameras.