An apparatus for detecting a pointer within a region of interest includes at least one pair of imaging devices. User preferences expressed on multiple domains, represented as pages in a social networking system, may be organized by concept and shared with advertisers, third-party developers, and other users of the social networking system using the metapages generated for the concepts. Each node includes hardware resources such as CPUs, memories and IO adapters. An impulse response mask may be determined based on the channel impulse response, and further applied to the channel impulse response to obtain a noise-reduced channel impulse response, which may be Fourier transformed to obtain a noise-reduced channel frequency response.