HueCode: A Meta-marker Exposing Relative Pose and Additional Information in Different Colored Layers

In this paper, HueCode, a meta-marker that robustly and simultaneously exposes the relative pose between a marker and a camera along with additional information, is proposed. It occupies the area of a single marker by overlaying multiple types of markers in different colored layers. Using perspective information from the first (most recognizable) type of element marker, the second or higher marker can be recognized with a better success rate. An experiment using a HueCode made from an ArUco marker and a QR code showed that the QR code within the HueCode is recognizable at an elevation angle of up to 15°, compared to 25° for a normal QR code. In addition, the versatility of HueCode is demonstrated using two robotic applications. The first is a lightweight estimation of absolute 6-DoF poses for mobile robots in a GNSS-denied environment, and the other is object annotation in two-dimensional image or three-dimensional space without any prior knowledge. The former realized pose estimation with a position error of less than 0.05 m, and the latter enabled annotation of a mirror and a transparent object, which are difficult for other sensors and machine learning to recognize.