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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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268 H. Josiński et al.<br />

selected attributes to number of attributes <strong>in</strong> an <strong>in</strong>put space. It can be noticed that<br />

greedy hill climb<strong>in</strong>g gives much more compact descriptors with lower number of<br />

features <strong>in</strong> comparison to genetic search. For <strong>in</strong>stance <strong>in</strong> case of variation cover<br />

Q=0.50 which gives 504 MPCA components, greedy hill climb<strong>in</strong>g selects 7 and<br />

34 features with wrapper and CFS evaluators respectively and genetic search selects<br />

194 and 78 components. The difference rises with <strong>in</strong>creas<strong>in</strong>g variation cover<br />

Q. In case of Q=0.80 and 10773 MPCA components greedy hill climb<strong>in</strong>g selects<br />

10 and 240 features and genetic search selects 1746 and 1903 components. It is so<br />

because of the complexity of considered selection problem. The <strong>in</strong>put set is very<br />

high dimensional and discrim<strong>in</strong>ative properties are scattered across MPCA components.<br />

It is extremely difficult to improve the classification accuracy by add<strong>in</strong>g<br />

a s<strong>in</strong>gle attribute, because only specified subsets of features have dist<strong>in</strong>ctive<br />

abilities. It is a reason why greedy hill climb<strong>in</strong>g with wrapper subset evaluator<br />

term<strong>in</strong>ates at first local extreme and it not able to discover efficiently <strong>in</strong>dividual<br />

gait features.<br />

Fig. 9. Compression rates<br />

However much more important assessment of selected MPCA components<br />

gives classification accuracy presented <strong>in</strong> Fig. 10. It shows percentage of correctly<br />

classified gaits of a test set <strong>in</strong> respect to MPCA variation cover Q and applied<br />

selection strategy. Globally best precision is 95%, obta<strong>in</strong>ed by 449 attributes selected<br />

from the <strong>in</strong>put set conta<strong>in</strong><strong>in</strong>g 29400 MPCA components for Q=0.87, which<br />

means 0.03% of compression rate, by hill climb<strong>in</strong>g search and CFS evaluator.<br />

Genetic search with CFS evaluator is very similar. It has 92.5% of classification<br />

precision and it has very similar dependency on a number of features of an <strong>in</strong>put<br />

space. Much worse results gives wrapper evaluator, especially if comb<strong>in</strong>ed with<br />

hill climb<strong>in</strong>g search, which is caused by the same reason as expla<strong>in</strong>ed <strong>in</strong><br />

compression rates analysis.

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