Optically imaging stylus for interacting with substrate having imageable position-coding pattern

An optically imaging stylus for interacting with a substrate having an imageable position-coding pattern, said position-coding pattern identifying a plurality of locations on the substrate, said stylus comprising:

• a stylus body;
• a nib for interacting with the substrate;
• an image sensor for imaging an area of the position-coding pattern;
• and
• a processor configured for:
• (i) inferring a perspective transform using perspective-distorted features of the imaged position-coding pattern, said features being perspective-distorted due to a tilt of the stylus;
• (ii) determining, from the imaged position-coding pattern, a rotational orientation of the stylus relative to the position-coding pattern;
• (iii) acquiring and decoding coded data contained in the imaged position-coding pattern, the decoded coded data identifying an imaged location on the substrate;
• (iv) calculating a nib position using:
• the imaged location, the perspective transform and the determined rotational orientation, said nib position being different than the imaged location;
• and
• (v) generating digital ink identifying the nib position.