Local Six-DoF Pose Refinement for Small-Diameter Cylindrical Markers Using Geometric Inconsistencies in the Unwrapped Cylindrical-Surface Image

This study proposes a local six-DoF pose-refinement method for small-diameter, pen-shaped instruments using geometric inconsistencies in unwrapped images of a paper-based cylindrical marker with an outer diameter of 8.3 mm after attachment. Full-circumference bands refine the cylinder-center position and longitudinal-axis orientation (five DoFs), while dot-edge image coordinates refine roll about the cylinder axis. The fixed 5+1-DoFscheme was evaluated in Geometry and Detector modes using 240 reference poses excluded from identification and tuning and 16 combined initial-error conditions per pose (3840 trajectories per mode). In the independent CG local-refinement evaluation, 17.60% of Detector-mode trajectories failed under the CG evaluation criteria; among 3164 algorithmically completed trajectories, 20 (0.63%) ended with greater normalized pose error than initially. In a separate end-to-end CG evaluation of 240 images, the current coarse initializer produced 157 coarse poses, 111 correct IDs, and 81 P0 completions; only 1 of 240 outputs also satisfied translation and rotation error thresholds of 0.10 mm and 0.10°, respectively. Thus, local-refinement and front-end/global capture performance must be evaluated separately. In K-transfer tests, matched rendering and processing intrinsic matrices showed no substantial deterioration, whereas intentional endpoint mismatch caused correction failure. For previously acquired real images, post-hoc nominal-setting analysis showed reduced XYZ RMSE after refinement, but did not constitute absolute-accuracy validation against an independent external reference.