RF-Copybook: A Millimeter Level Calligraphy Copybook based on commodity RFID

As one of the best ways to learn and appreciate the Chinese culture, Chinese calligraphy is widely practiced and learned all over the world. Traditional calligraphy learners spend a great amount of time imitating the image templates of reputed calligraphers. In this paper, we propose an RF-based Chinese calligraphy template, named RF-Copybook, to precisely monitor the writing process of the learner and provide detail instructions to improve the learner's imitating behavior. With two RFID tags attached on the brush pen and three antennas equipped at the commercial RFID reader side, RF-Copybook tracks the pen's 3-dimensional movements precisely. The key intuition behind RF-Copybook's idea is that: (i) when there is only direct path signal between the tag and the antenna, the phase measured at the reader changes linearly with the distance, (ii) the reader offers very fine-grained phase readings, thus a millimeter level accuracy of antenna-tag distance can be obtained, (iii) by combing multiple antenna-tag distances, we can quantify the writing process with stroke based feature models. Extensive experiments show that RF-Copybook is robust against the environmental noise and achieves high accuracies across different environments in the estimation of the brush pen's elevation angle, nib's moving speed and position.