Group Level Activity Recognition in Crowded Environments across Multiple Cameras

Environments such as schools, public parks and prisonsand others that contain a large number of people are typi-cally characterized by frequent and complex social interac-tions. In order to identify activities and behaviors in suchenvironments, it is necessary to understand the interactionsthat take place at a group level. To this end, this paper ad-dresses the problem of detecting and predicting suspiciousand in particular aggressive behaviors between groups ofindividuals such as gangs in prison yards. The work buildson a mature multi-camera multi-target person tracking sys-tem that operates in real-time and has the ability to han-dle crowded conditions. We consider two approaches forgrouping individuals: (i) agglomerative clustering favoredby the computer vision community, as well as (ii) decisiveclustering based on the concept of modularity, which is fa-vored by the social network analysis community. We showthe utility of such grouping analysis towards the detectionof group activities of interest. The presented algorithm isintegrated with a system operating in real-time to success-fully detect highly realistic aggressive behaviors enacted bycorrectional officers in a simulated prison environment. Wepresent results from these enactments that demonstrate theefficacy of our approach.