By using computers to pre-screen the cameras, only views with some event of interest to the operators will be selected to the call-up monitors. [0223] System Operation [0224] The computer interface between the two systems, i.e. PCS system 10 and CCTV subsystem 12, functions in the following manner, with reference to FIG. 2: PCS system 10 requests a camera call up to one of the inputs to quad split