Patent ID: 7136054

Claim:
A method of calibrating a digital pen, which includes a pen tip and a camera, and of mapping a location of a center of a camera-captured image to a location of the pen tip, the method comprising: generating a calibration parameter based on a plurality of images captured by the digital pen's camera by placing the pen in a plurality of different orientations while keeping the pen tip at a substantially fixed location L pentip on a positionally encoded surface, wherein the calibration parameter is generated based on a plurality of iteratively generated estimates of the calibration parameter; and using the calibration parameter to map the location of the center of the camera-captured image to the location of the pen tip so that a stroke written by a user on the positionally encoded surface can be recovered at a location within an electronic copy of the positionally encoded surface, wherein the position of the recovered stroke within the electronic copy corresponds to a plurality of locations of the pen tip as the user was writing the stroke on the positionally encoded surface.