US Patent 7649524 Tracking window for a digitizer system

A digitizer apparatus for digitizing user interactions, for example detecting locations of physical objects, comprises: sensing elements, spread across a sensing area, configured for sensing the user interactions, say involving a stylus or like object, and a controller, associated with the sensing elements, configured to dynamically select a tracking window for the interaction, the tracking window comprising a subset of the sensing elements which are activated for sensing the object. The window is selected to center on the interaction based on e.g. last known location data, and thereby save processing resources by sampling only the minimum number of sensing elements necessary at any time.