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  Douillard, B., Fox, Dieter, Ramos, F.T. & Durrant-Whyte, H.F.
Classification and Semantic Mapping of Urban Environments
In The International Journal of Robotics Research, no. In Press, 2010

Abstract
This paper addresses the problem of classifying objects in urban environments based on laser and vision data. It proposes a framework based on Conditional Random Fields (CRFs), a flexible modelling tool allowing spatial and temporal correlations between laser returns to be represented. Visual features extracted from colour imagery as well as shape features extracted from 2D laser scans are integrated in the estimation process. The paper contains the following novel developments: 1) a probabilistic formulation for the problem of exploiting spatial and temporal dependencies to improve classification; 2) three methods for classification in 2D semantic maps; 3) a novel semi-supervised learning algorithm to train CRFs from partially labelled data; 4) the combination of local classifiers with CRFs to perform feature selection on high dimensional feature vectors. The system is extensively evaluated on two different datasets acquired in two different cities with different sensors. An accuracy of 91% is achieved on a 7-class problem. The classifier is also applied to the generation of a 3km long semantic map.

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