Patent ID: 8100329

Claim:
A method of interacting with a printed substrate, the method comprising the steps of: providing the printed substrate, said substrate having printed thereon: human-readable information and a position-coding pattern comprising a plurality of target elements and coded data, said coded data identifying an identity of the substrate and a plurality of locations on the substrate, the human-readable information being coincident with the position-coding pattern; interacting with the substrate using an optically imaging pen, said pen having a nib; optically imaging target elements and coded data; calculating a position of the nib; and generating digital ink in the pen, said digital ink being indicative of the identity of the substrate and the position of the nib relative to the substrate; and sending the digital ink to a computer system such that the computer system identifies the interaction with the substrate, wherein the position of the nib is calculated using the coded data, a perspective transform and a known spatial relationship between an optical axis of the pen and the nib, and wherein the perspective transform is determined using the imaged target elements which are perspective-distorted due to a tilt of the pen.