Biomedical Engineering Reference
In-Depth Information
Fig. 8.2
Common marker placement used in Biomechanics [
39
,
40
] to retrieve joint centers and
to use anthropometric tables
skin displacements artefacts, this method will also provide the system with virtual
bones that could change in length at each frame.
Another approach consists in generalizing the above idea to the whole skeleton.
Let us consider that there exists a model of the skeleton based on rigid bodies and
perfect joints (such as ball and socket and pivot joints). Knowing the external markers
m
i
in each local reference frame, the distance between m
i
and m
i
depends on the size
of the body segments and the angles
(where n is the number of degrees
of freedom of the model). If there are enough markers on the body compared to the
number of unknowns (i.e. number of degrees of freedom and of body segments), the
problem can again be rewritten as a global optimization problem [
15
]:
θ ={θ
...
n
}
1
2
m
m
∗
T
m
m
∗
1
ith m
∗
=
ar
g
min
−
−
w
f
(θ,
l
)
θ,
l
