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[Studies in Computational Intelligence 481] Artur Babiarz, Robert Bieda, Karol Jędrasiak, Aleksander Nawrat (auth.), Aleksander Nawrat, Zygmunt Kuś (eds.) - Vision Based Systemsfor UAV Applications (2013, Sprin

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242 H. Josiński et al.<br />

The previously computed CCR values were averaged for PCA as well as for each<br />

LLE variant separately, with regard to the given value of d (see Fig. 9) and to the<br />

given value of N (see Fig. 10). The complete range of N was taken <strong>in</strong>to account,<br />

whereas the set of dimensionalities was limited to powers of 2 from 4 to 256.<br />

Fig. 9. Dependency between average CCR and dimensionality d for PCA and all LLE<br />

variants<br />

Fig. 9 shows that the 100 % accuracy was obta<strong>in</strong>ed for the reduced<br />

dimensionality d = 256 for both methods with the exception of the LLE variant<br />

us<strong>in</strong>g k = 80 nearest neighbors (avg(CCR) = 95 %). As it was aforementioned,<br />

accord<strong>in</strong>g to expectations the accuracy rema<strong>in</strong>ed equal to 100 % for d = 512<br />

regardless of the variant of dimensionality reduction. It is worthwhile mention<strong>in</strong>g<br />

that the accuracy of the GP-LVM and HMM-based classification of the CASIA<br />

gait sequences, reported <strong>in</strong> [21] was equal to 86 %. However, <strong>in</strong> this case the<br />

analyzed sequences were not limited to the “parallel-oriented” subset. Although <strong>in</strong><br />

the 3 follow<strong>in</strong>g cases: N = 2, 3, 5 accuracy obta<strong>in</strong>ed by the PCA was equal to 100<br />

% already for d = 16, but tak<strong>in</strong>g the average accuracy <strong>in</strong>to consideration the LLE<br />

outperforms the PCA.<br />

In particular, the maximum average value of the CCR equal to 88.57 % was<br />

achieved for N = 7 states by means of the LLE us<strong>in</strong>g k = 40 nearest neighbors.<br />

Admittedly, it was mentioned <strong>in</strong> [25] that the LLE algorithm can only be<br />

expected to recover embedd<strong>in</strong>gs whose dimensionality is strictly less than the<br />

number of neighbors (d < k), but the results of classification of the CASIA gait<br />

sequences show that <strong>in</strong> opposite case the reconstruction error is small enough to<br />

obta<strong>in</strong> acceptable classification accuracy. This observation confirms the remark<br />

that the exact relation between k and the faithfulness of the result<strong>in</strong>g embedd<strong>in</strong>g<br />

rema<strong>in</strong>s an important open question [25].

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