From On-Going to Complete Activity Recognition Exploiting Related Activities

Activity recognition can be seen as a local task aimed at identifying an on-going activity performed at a certain time, or a global one identifying time segments in which a certain activity is being performed. We combine these tasks by a hierarchical approach which locally predicts on-going activities by a Support Vector Machine and globally refines them by a Conditional Random Field focused on time segments involving related activities. By varying temporal scales in order to account for widely different activity durations, we achieve substantial improvements in on-going activity recognition on a realistic dataset from the PlaceLab sensing environment. When focusing on periods within which related activities are known to be performed, the refinement stage manages to exploit these relationships in order to correct inaccurate local predictions. © 2010 Springer-Verlag Berlin Heidelberg.