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Cenciotti Luca
05-13-2001, 02:05 AM
Dear BIOMCH-L Readers,

recently I requested help in finding informations and articles about
video based
motion analysis. Here's the original message:
*************
I'm looking for comparative studies or articles about the use of video
based motion analysis systems. The topics of interest are upper arm
motion analysis and gait analysis. I would also like to collect any
opinion about the main advantages and disadvantages of video based
motion analysis, compared with electromagnetic or optical tracking
systems.
Thanks in advance,
Luca Cenciotti
*************

Thanks very much to all those who replied. A summary of main replies
follows.

* From: Chris Stevens
Three system comparison meetings were held in Japan, in 1993, 1995 and
1999. The first two have been published. (Ehara Y 1995)and (Ehara Y
1997). A report on the 1999 meeting was obtained via the web (Ehara
2000). The methods used were basically the same on each occasion,
although becoming more elaborate.
Using a human to move a marked device in prescribed ways, the main
measurements were:
1. Distance between two marked points (called distance accuracy), in the
vertical, forward and medio-lateral directions during movement.
2. The accuracy with which the system measured an a known angle (called
angle accuracy) during movement.
3. Position of each of the two markers, when markers are stationary
(called noise).
4. Time taken to calculate 3D coordinates and display a 3D stick figure
after measurement (called Process time)
References:
Ehara Y, H. F., S Miyazaki, S Tanaka, S Yamamoto (1995). “Comparison of
the performance of 3D camera systems.” Gait and Posture 3(September):
166-169.
Ehara Y, H. F., S Miyazaki, M Mochimaru, S Tanaka, S Yamamoto (1997).
“Comparison of the performance of 3D camera systems II.” Gait and
Posture 5: 251-255.
Protocol of 1999 Japanese meeting can be found on:
http://www.aist.go.jp/NIBH/ourpages/comparison99/protcol99.html
Details of systems tested at 1999 Japanese meeting can be found on:
http://www.aist.go.jp/NIBH/ourpages/comparison99/comp99.html

In a comparison carried out in the USA, (Richards, J. G. (1999) “The
measurement of human motion: a comparison of commercially available
systems.” Human Movement Science 18: 589-602) a device was used that
allowed the measurement of :
1. the distance between two rotating, constantly visible markers
2. motion relative to a static marker
3. position-time histories of markers visible to alternating sets of two
or three cameras
4. motion in close proximity to a second marker

Other papers have considered one system (Klein P 1995) for Ariel and
(Linden DWV 1992) for Motion Analysis.
A survey of the types of gait instrumentation commercially available has
been carried out (Bontrager 1998). This did not formally test systems
but gives some information on them.
References:
Klein P, D. H. J. (1995). “Accuracy of three dimensional linear and
angular estimates obtained with the Ariel performance analysis system.”
Arch Phys Med Rehab 76: 183-189.
Linden DWV, C. S., Hubbard RL (1992). “Reproducability and accuracy of
angle measurements obtained under static conditions with the Motion
Analysis Video System.” Physical Therapy 72: 300-305.
Bontrager E. L. (1998). Instrumented Gait Analysis (Review of
Instrumented Gait Analysis Systems). Gait Analysis in the Science of
Rehabilitation. Joel A. De Lisa, VA Rehabilitation Research &
Development Service: 11-32

* From Andy Brammall
In terms of differences between systems, I believe that it is important
to remember that there are several factors to consider - this would
include:
1) Price/performance
2) Volume available for study
3) Accuracy and precision of measurements - is this even over the
whole of the volume studied?
4) Effects of environment on accuracy of system, eg. effect of
metallic objects on magnetic systems, effect of ambient lighting, is it
possible to use markers on the subject etc.
5) Sampling frequency
6) Number of points that can be measured
7) Ability to interface with other software/hardware
8) Effect of using multiple sensors/cameras
9) Time taken to collect and process the data
10) Ability to deal with occluded markers or points, or to resolve
problems encountered during data collection (eg switched markers)

* From Elizabeth Bradshaw
The main issue regarding the real-time automated systems vs. video is
the measurement space and analysis time. For example, I can measure the
step parameters for a 50m long jump approach using video in the field,
where as, with a real-time automated system I can only measure about 4m
and I must bring the athlete into the lab. The second issue with the
automated system is the change in enviroment by bringing the athlete
into the lab, and also the use of markers. This can alter the kinematics
if not controlled.


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Luca Cenciotti
Electrical Engineer
Arts Labs - Scuola Superiore Sant'Anna
via Carducci, 40
56127 Pisa, Italy
Phone +39 050 883405
Fax: +39 050 883402
E-mail: l.cenciotti@mail-arts.sssup.it
Web: http://www-arts.sssup.it
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