3D motion analysis
A three-dimensional analysis has typically to be done for complex, rotating or simi-
- golf swing
- hammer throwing
- martial arts
Scientists in sports biomechanics and medicine often use 3D analysis in order to
describe a body's movements in three dimensional space. If you want to do a simi-
lar motion analysis you have to use more than one camera, because each anatomic
landmark (marker) has to be identified in at least two cameras.
Although 3D motion analysis can be done using only two cameras, most movements require
four or more cameras.
With 3D coordinates six degrees of freedom (6 DOF) can be computed, i.e. rotations
around all three axes of a segment or a joint can be determined as well as the exact
Two different methods are commonly used in commercial motion capture systems:
Static calibration frame
For a static calibration an object with known dimensions (e.g. a cube, cuboid or
simi- lar object) is placed into the cameras field of view. The size of the calibration
frame should cover the total movement space.
The objects shape is then digitized using manual or automatic marker detection for
the calibration points.
For most algorithms it is not necessary that all cameras see the same set of calibration
A static calibration needs approx. 1-3 minutes per camera.
Dynamic calibration (wand calibration)
During dynamic calibration the user moves a pole with attached markers which have
to be seen by all or a subset of the cameras.
The pole is moved until the complete movement space is covered.
A dynamic calibration needs a couple of minutes or more, depending on the systems
detailed requirements and its real-time tracking capabilities.
2D motion analysis
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