AcTag: Opti-Acoustic Fiducial Markers for Underwater Localization and Mapping

Fiducial markers are important tools for robotic navigation and imaging, enabling accurate localization and tracking of objects in challenging environments. In this paper, we present AcTag, a new fiducial marker design for use underwater with imaging sonar and cameras, as well as a method for the detection of AcTags within acoustic images. High amounts of noise and a nonlinear projection model make it difficult to use imaging sonar in autonomous localization and mapping. In order to expand the use of imaging sonar in autonomous underwater vehicles, our markerb design and detection algorithm for sonar images facilitate the identification of four unique landmarks per tag, and provide relative range and azimuth values to each landmark. We evaluate our marker and detection algorithm with simulated and real-world sonar data, reporting on the false positive and true positive rates, as well as the estimated error for the range and azimuth estimates per landmark. We also release an open-source library for generating tag families and detecting the tags.