1. Introduction
The identification of motion flows within dense crowds of people in surveillance video sequences is an essential tool in crowd safety and crowd control tasks. Surveillance video of crowded scenes exhibit complex crowd behaviors even under normal situations. For example, crowd flows in large congested train stations can appear chaotic. However, it is often the case that low dimensional dynamical structures exist in the observed flow. Such structures are desirable to identify and segment from unstructured and transient flows. The automatic identification of different types of crowd flows aids in the monitoring and prediction of hazardous situations in crowded environments. Similarly, the identification of anomalous flows in traffic scenes helps management facilities predict and react to potential congestion.