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
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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