Asterisk and Obelisk: Motion Codes for Passive Tagging

Machine readable passive tags for tagging physical objects are ubiquitous today. We propose Motion Codes, a passive tagging mechanism that is based on the kinesthetic motion of the user's hand. Here, the tag comprises of a visual pattern that is displayed on a physical surface. To scan the tag and receive the encoded information, the user simply traces their finger over the pattern. The user wears an inertial motion sensing (IMU) ring on the finger that records the traced pattern. We design two motion code schemes, Asterisk and Obelisk that rely on directional vector data processed from the IMU. We evaluate both schemes for the effects of orientation, size, and data density on their accuracies. We further conduct an in-depth analysis of the sources of motion deviations in the ring data as compared to the ground truth finger movement data. Overall, Asterisk achieves a 95% accuracy for an information capacity of 16.8 million possible sequences.