Description of APAS-XP Software 6/17/2002

The APAS-XP software is designed to streamline and automate the process of biomechanical analysis from the starting point of collecting video data from multiple cameras to the point of displaying 3D image data.

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. A marker may disappear for a few frames in 3D but one should strive to have 3D of all markers throughout the activity. Should a marker disappear for longer times the operator may manually notify the software of a re-appearance.

APAS-XP is designed to facilitate the processing of a subject starting with the collecting of the video of interest and ending with the displaying of 3D figures. Transitions between the various APAS modules occur seamlessly without the operator having to manually exit one module and start another. Also the relevant files created in one module are automatically passed to the next automatically.

For users of APAS-XP, the starting point of an analysis is the collecting of video data of the subject performing the activity of interest. The module CapDV will collect simultaneously up to 6 DV cameras directly to the hard disk. In the process the video files can be automatically trimmed based on a synch event recorded in the audio of the captured video. For activities that do not generate an impact sound that is picked up on the audio, a simple clap of the hands works adequately.

With captured video files ready, the operator selects the "Digitize" button. CapDV will transition to the Digitizing Module. All the user needs to do is to specify the activity of interest. The Digitizing Module will create a digitizing view for each AVI file create by CapDV and display the proper video. The operator then digitizes the control points or reads the control point digitizing from another sequenceand starts the auto-digitizing function and the software will automatically digitize the views using the 3D Auto-Track algorithm. When the auto-digitizing completes, the Digitize Module can be configured to process the digitizing into 3D coordinates and to start either the Display or APASView module displaying a stick figure view of the 3D figure.

For APAS-XP users the Digitize Module can be configured to:

1) When a project is created the software can

a) create no views

b) create a single view

c) create multiple views

The created multiple views is also a new menu option. When multiple views is selected a dialog appears which expedites the assigning AVI files to views and assigning View descriptions.

2) When opening an existing project the software can

a) open no views

b) open last view created

c) open all views

3) There are various processing options

a) Transform/Smooth silently when transform has been selected. No dialog of options will appear, merely a status box.

b) Transform/Smooth upon completion of 3D AutoTrack.

c) Run Display/APASView using 3D file created in b).

4) User has a choice of selecting either Display or APASView as the module to run when "Analyze" is selected.

Also when performing tasks such as reading control points or opening AVI files, the system can manage multiple files simultaneously with the user only having to specify one file/view and the software will manage the remaining.

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