Low-cost and robust docking angle estimation for miniature USVs through the integration of camera and multi-zone ToF sensor

Autonomous docking of miniature unmanned surface vehicles (USVs) requires compact, low-cost, and robust sensing for estimating angles within short ranges. To fulfill these requirements, this work presents a dual-sensing strategy that combines a camera and an 8 × 8 multi-zone time-of-flight (ToF) sensor. In this strategy, the camera-based method can estimate the docking angle through calibrated AprilTag pose estimation, while the ToF-based method can derive angular information from column-wise range gradients. Experiments covering 20–80 cm and 10°–50° demonstrate that both methods can achieve reliable angle estimation, with an overall mean absolute error (MAE) of angle below 1.5°. The results further show complementary performance of the proposed design: ToF sensing is more stable at small angles while camera-based estimation performs better at larger angles. Moreover, experiments validate the robustness and practical use of the proposed system under varying illumination scenarios.