2008 Final Year Project – 1st Term Report - The Chinese University ...

3.5.3.3 WHY DYNAMIC TIME WARPING?
Department of Computer Science and Engineering, CUHK
2007 – 2008 Final Year Project – 1st Term Report
When compared to Euclidean Distance algorithm, Dynamic Time Warping allows
non-linear mapping, thus non-linear variations on time or speed can be overcome. We
illustrate the advantage of Dynamic Time Warping with an example below.
Fig. 3.13 Comparisons between Euclidean Distance algorithm (graph A) and
Dynamic Time Warping (graph B) [11]
The figure above shows how a stored curve (the curve on top) is compared with
the input curve. Obviously 2 curves are doing the same thing. However, in the stored
curve, the 4 crests occur consecutively; while in the input curve, 2 crests occur first,
and then followed by a short period of rest, and another 2 crests occur.
As shown in graph A, if Euclidean Distance algorithm is used, the errors will be
large due to appearance of crests at different time. On the other hand, if Dynamic Time
Warping is used, the time difference in the occurrence of crests can be overcome since
one point can map to multiple points. That means crests at the one curve are mapped
to corresponding crests at the other curve. The computed error will then be much
smaller, and thus the input can then be classified at a higher accuracy.
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(A)
(B)