4.4. Object tracking 
Two different projects indicate the potential of 
CCD camera based methods for object tracking. 
For the determination of 3-D velocity fields in 
turbulent flow a three CCD camera arrangement 
was used to record laser sheet illuminated particles 
in a laboratory water channel (Papantoniou, Maas, 
1990). The technique is fully automatic, uses a 
multimedia photogrammetric approach and can 
track the particles with high spatial precision and 
reliability, and very good temporal and spatial 
resolution. About 700 particles can be positioned 
and tracked over as many as 350 video cycles with 
a tested accuracy of [i x y = 0.04mm and fi z = 
0.04mm in an object space volume of 150 x 150 x 
18 mm 3 . 
from comparison with the true value of the distance 
from 93 ruler positions. 
5. Conclusions 
It is our experience that the modular concept of a 
workstation-based digital photogrammetric station 
is a very appropriate and useful approach for a 
research and development group. The fast progress 
in the development of general computer 
components on the hardware and software side 
allows for permanent and timely upgrading of the 
system. So far we have not encountered any 
problem with upward-compatibility. As an 
example, the transfer of our C software packages 
from Sun-3 (Motorola MC68020 processor) to Sun 
Figure 9: Biomechanical application. Trajectories of markers overlaid onto a sequence of CCD frames of 
a walking person. 
Related to biomechanical applications a person was 
marked with retro-reflective targets. Thus walking 
through our large testfield the trajectories of these 
markers were determined by three CCD cameras, 
the frames of which were acquired simultaneously 
and recorded on video tapes. Figure 9 shows the 
trajectories overlaid onto a sequence of images. 
Problems of occluded and only partially imaged 
targets deserved special consideration. The person 
was carrying a 50 cm long ruler with one marker at 
each end. An RMS error of 1.7 mm was achieved 
SPARCstation (SPARC RISC processor) 
technology needed only recompilation. Our 
independence of any special equipment 
manufacturers and the use of many hardware and 
software standards guarantees for fast and 
uncomplicated further development of our system’s 
components and for easy integration of new 
algorithms and procedures. Other important factors 
are the ease of access to third party hard- and 
software and the compatibility with external groups 
and systems.