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Young-hoo Kwon, Ph.d.
09-30-2002, 12:01 AM
Dear colleagues,

We are currently reviewing different methods of locating the hip joint
center. It seems to me that most of the indirect methods basically fall into
two categories: (1) methods based on the pelvic markers, in some cases in
conjunction with anthropometric measurements, and (2) numerical methods such
as the functional method originally reported by Cappozzo (1984).

The methods that fall into group 1 include

Tylkowsky et al. (1982)
Andriacchi et al. (1980)
Bell et al. (1990): hybrid of Tylkowsky and Andriacchi
Davis et al. (1991)

Studies based on the numerical method (rotational method) include

Piazza et al. (2001)
Leardini et al. (1999)
Bell et al. (1990)
Cappozzo (1984)

I am particularly interested in the functional method which is based on the
least square approximation of

L = sum[ ( (xi-xc)^2 + (yi-yc)^2 + (zi-zc)^2 )^0.5 - R ] ==> min

where xi, yi, zi = the coordinates of a marker on the thigh (or centroid of
several markers) at frame i described in the pelvis reference frame, xc, yc,
zc = hip joint center described in the pelvis reference frame, and R =
radius of the sphere formed by this marker about the hip joint center.

Can anyone suggest a numerical alogorithm that will perform the
aforementioned least square approximation effectively. I could not find any
specifics on this in the published papers. I am in the process of writing a
program to do this and I'd like to compare different algorithms including
mine. Any pointers or suggestions will be appreciated. As usual, I will post
the summary on Biomch-L.

Thanks in advance!

Young-Hoo Kwon
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- Young-Hoo Kwon, Ph.D.
- Associate Professor, Dept. of Kinesiology
- Director, Biomechanics Laboratory
- Texas Woman's University
- P.O. Box 425647
- Denton, TX 76204-5647
- Phone: (940) 898-2598
- Fax: (940) 898-2581
- Email: ykwon@twu.edu
- Homepage: http://kwon3d.com
- Korean kwon3d eGroup: http://kwon3d.com/korean/eGroup_kr.html
- Int'l kwon3d eGroup: http://kwon3d.com/eGroup_i.html
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