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253 
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positions of joint axes with related segmental boundaries on 
images of individual persons. Data acquisition by 
photogrammetry is fast and bothers the patients but little. 
Data processing in photogrammetry has long been so 
laborious that this has prevented regular application to 
accomplish such tasks. To what degree has this changed by 
now and how will it develop in the near future? 
In order to evaluate the feasibility of obtaining individual 
body parameters by  photogrammetry for subsequent 
inclusion in high quality kinetic gait analysis, a pilot study 
was performed on a collaborative basis including the 
Biostereometrics Laboratory of the University of Akron, 
Ohio, a photogrammetry laboratory at the University of 
Illinois in Champaigne-Urbana, the Bioengineering Centre of 
the University of Strathclyde in Glasgow and our Institution. 
METHODS 
10 normal individuals age 8 - 18 years as well as 10 age and 
sex matched patients with spastic diplegia have been 
examined in brief swim wear. For data acquisition, 
orthopedic medical examination was followed by weighing 
and by marking 107 anatomical sites with stick-on reflective 
markers defining joint locations, segmental boundaries and 
other landmarks. 
For evaluation of Human Segmental Body Volumes and 
Inertial Properties using stereophotogrammetry, data were 
collected by means of stereophotogrammetry for the 
determination of segmental body volumes and their 
respective inertial tensors. The methods of simultaneous 
recording of front and rear stereopairs requires the use of two 
pairs of stereometric cameras linked together by 
electro-mechanical shutter releases. Stroboscopic flashlamps 
illuminate the subjects and are used to project a random 
pattern onto the surface of the subjects to increase the surface 
contrast necessary for data reduction. For the purposes of this 
investigation, wide angle stereometric cameras (Hasselblad 
Superwiede Angle) were used. The cameras are equipped 
with Biogon lenses having a focal length of 38 mm. The 
cameras were modified for glass plates using film planes 
containing fiducial markers. All subjects were photographed 
while standing in a control reference frame which provided 
spatial information to enable the linkage of front and rear 
stereomodels and to provide proper scaling information for 
the data analysis. 
Following development and enlargement of the exposed 
stereopairs, the data were reduced using a modified Kern 
PG-2 stereoplotter. The plotter allowed the operator to obtain 
coordinate triplets for a series of points on the surface of the 
subject's photographic image. The methodology used has 
been comprehensively described by Herron et al. (1974, 
1975). To insure ease in computation of the volumentric 
information, the points representing the body surface were 
collected in parallel crossections approximately 2.0 cm apart 
and lying perpendiculare to the long axis (cranial-caudal) of 
the body. In addition to the crossection data used to describe 
the shape of each body segment for computation of volume, 
further coordinates were collected to provide planes of 
segmentation for separating (analytically) major body parts 
such as the thigh, shank or foot. These extra landmark 
coordinates were used to describe anatomical axis systems 
necessary for translation and transformation of coordinate 
systems in the kinetic data analysis phase of the study. . 
  
  
Fig.1: 13 segment model, photogammetric reconstruction 
from 2 cm slices. 
Resistance to the change in angular velocity depends upon 
the mass of the body and its distribution about the centers of 
rotation. This resistance is referred to as the mass moment of 
inertia (I). The geometric properties, hence shape or volume 
distribution, determine the extent to which each particle of 
mass contributes to the moment of inertia. The mass moment 
of inertia about an axis greatly determines the dynamics of 
the body segment undergoing simple rotation. Because the 
body is three dimensional an inertial tensor is produced to 
describe the moments of inertia about the three orthogonal 
axes. Because only one inertial tensor exists for a 
non-symmetric body in which the off diagonal elements are 
zero, we can describe this entity as containing the principal 
moments of inertia, which greatly enhance the comparison of 
the mechanical properties of motion from one subject to 
another. Based upon a uniform density assumption, the 
segmental mass and center of gravity could be determined 
and therefore enable a comprehensive joint kinetic analysis to 
complement the traditional gait analysis techniques. 
Data evaluation and processing of the static tests consisted 
in constructing a 13 segment body model for each of the 20 
test persons with calculation of segmental volumes, 
segmental masses and mass centers from the two pairs of 
stereophotographs. A pair of 16 mm film images with DLT 
calibration served to link 3D body marker positions obtained 
in the global axis system with the laboratory space coordinate 
system as used for gait recordings. Marker positions where 
manually digitized from projected film images.