Introduction to Sports Biomechanics: Analysing Human Movement ...

Figure 4.4 A typical calibration object for three-dimensional videography.
QUANTITATIVE ANALYSIS OF MOVEMENT
For three-dimensional analysis, there are other potential error sources, although several
of those above are partly or wholly overcome.
Relating the two-dimensional video image coordinates to the three-dimensional
movement–space (‘real world’) coordinates may be a source of error. Several
methods of doing this will be considered below but they all present problems. Use
of an array of calibration points, such as a calibration object (Figure 4.4) is probably
the most common method. Errors within the calibration volume can be accurately
assessed, while those outside that volume will be larger and more difficult to assess.
Errors will increase with the ratio of the size of the movement space to that of the
image.
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