The level of security at a facility is directly related to how well the facility can keep track of "who is where?" The "who" part of this question is typically addressed through the use of face images for recognition either by a person or a computer face recognition system. The "where" part of this question can be addressed through 3D position tracking. The "who is where" problem is inherently multi-scale, wide angle views are needed for location estimation and high resolution face images for identification. A number of other people tracking challenges like activity understanding are multiscale in nature.

An effective system to answer "who is where?" must acquire face images without constraining the users and must closely associate the face images with the 3D path of the person. Our solution to this problem uses computer controlled pan-tilt-zoom cameras driven by a 3D wide-baseline stereo tracking system. The pan-tilt-zoom cameras automatically acquire zoomed-in views of a person’s head, while the person is in motion within the monitored space.