A few weeks ago Sergey Brin was on the Gavin Newsom Show showing off his Project Glass prototype. If you remember, he was using a physical trackpad for navigation. Well Google just received a patent on it.
They actually call it a finger-tracking input sensor and here is how they describe it:
In another embodiment, the input device may include a touch-sensitive pad configured to sense at least one of a position and movement of a finger along a planar direction relative to a surface of the input device via capacitive sensing, resistance sensing, and/or via a surface acoustic wave (SAW) process. In yet another embodiment, the input device may be an optical imaging device and the surface of the optical imaging device a lens provided at an outer surface of the optical imaging device. By capturing images many times per second, the optical imaging device can accurately detect a position and movement of a finger along a planar direction relative to the lens surface of the input device.
Interestingly enough Google filed for the patent five days before going on the show.