1. A system to support 3-D multi-camera video monitoring, comprising: a content analysis module operable to generate a 3-D semantic layout of a site under surveillance; a background subtraction module operable to detect and segment a moving object in video streams from a plurality of cameras; a motion tracking module operable to track the moving object in the video streams; a blending module operable to highlight the foreground region of the video streams by alpha blending; and a rendering module operable to integrate the video streams after alpha blending with the semantic layout into a 3-D immersive environment.