View Full Version : Re: Surface markers in 3D analysis

Christopher P Sherwood
12-09-1995, 01:02 AM
On Fri, 8 Dec 1995, Jesus Dapena wrote:

> > For one, it makes the use of live volunteers reasonable! Implanted
> markers are fine for cadaver studies. *In vivo* needs surface markers.
> >
> > Sincerely,
> >
> > Carolyn Small
> Well, there are other options too. For instance, the researcher can
> estimate the locations of the internal joints directly from the projected
> images. You sacrifice some of the accuracy in the digitization of the
> landmarks, but you can get 3D coordinates of internal landmarks without
> having to implant anything in your subjects. In fact, in some situations it
> is not possible to put even surface markers on the subjects; for instance,
> this is generally the case if you film or videotape a major sport
> competition.
> ---
> Jesus Dapena
> Department of Kinesiology
> Indiana University
> Bloomington, IN 47405, USA
> 1-812-855-8407 (office phone)
> dapena@valeri.hper.indiana.edu (email)

Using joint center locations is just one method of calculating in vivo
human body kinematics. Another method is to use 3 (or more) markers
attached to each body segment, and assuming each segment is a rigid body,
the 6 DOF between each segment can be calculated. If the subject is
filmed in a known position, in which all joint angles are
defined, all joint angles can be calculated with respect to their defined
reference positions. This method allows for the use of surface markers
which can be positioned without reference to any bony landmarks or joint
centers, and often these marker positions can be adjusted to allow for
better viewing by multiple cameras.

Chris Sherwood
Department of Bioengineering
University of Pittsburgh

567 Benedum Engineering Hall
Pittsburgh, PA 15261 USA

(412) 624-9776