The complementary advantages of cameras and multi zone ToF sensors enhance the accuracy and reliability of estimating the berthing angle for miniature USV

This study proposes a low-cost berthing angle estimation method that integrates monocular cameras and multi zone ToF sensors, utilizing the complementary advantages of the two sensors to improve measurement accuracy and reliability. The experimental results show that this method achieves an average absolute error of 0.64 ° under different distance and angle conditions, providing an economical and reliable technical solution for precise berthing perception of miniature unmanned surface vehicles (USVs).This study proposes a low-cost berthing angle estimation method that integrates monocular cameras and multi zone ToF sensors, utilizing the complementary advantages of the two sensors to improve measurement accuracy and reliability. The experimental results show that this method achieves an average absolute error of 0.64 ° under different distance and angle conditions, providing an economical and reliable technical solution for precise berthing perception of miniature unmanned surface vehicles (USVs).

With the development of smart ports and autonomous navigation technology, miniature unmanned surface vehicles (USVs) have shown broad application prospects in areas such as waterway inspection and environmental monitoring. However, ensuring that these miniature USVs can return smoothly to their berths remains a challenge. When the unmanned boat gradually approaches the berth, it is not enough to only know the distance, but also to accurately determine the relative angle between itself and the berth. Especially during the close range berthing phase, even small angular deviations may affect the alignment effect. Traditional high-precision perception devices such as LiDAR are usually expensive and bulky, making it difficult to meet the low-cost and compact design requirements of miniature USVs. Therefore, how to utilize limited hardware resources to achieve accurate and reliable angle perception has become an important challenge for autonomous berthing of miniature USV.

A research team from the Hong Kong University of Science and Technology (Guangzhou) has proposed a low-cost berthing angle estimation method that integrates monocular cameras with multi zone Time of Flight (ToF) sensors to address this issue. This scheme cleverly utilizes the complementary characteristics of two sensors. The camera estimates docking angles by detecting visual markers and performs better at larger angles, but its performance is sensitive to lighting conditions and occlusion. In contrast, the ToF sensor estimates docking angles through active distance measurements, providing greater stability under low-light conditions and at smaller docking angles. The research team combines the measurement results of two sensors through a weighted fusion strategy, fully leveraging their respective advantages to improve the accuracy and reliability of angle estimation, while maintaining a low-cost and compact hardware configuration.

To evaluate the effectiveness of the proposed method, the research team conducted experiments at distances ranging from 20 to 80 cm and reference angles from 10° to 50°, along with additional tests under varying lighting and partial-obstruction conditions. The results showed that both individual sensing methods achieved an overall mean absolute error (MAE) below 1.5°, while the fusion method achieved an MAE of 0.64° and a root mean square error (RMSE) of 0.81° across the evaluated distance–angle configurations, demonstrating the effectiveness of the dual-sensor fusion approach. These findings demonstrate that by leveraging the complementary advantages of low-cost sensors, high-precision and reliable close range angle estimation can also be achieved, providing a compact, economical, and potentially applicable technical solution for attitude perception of autonomous berthing of micro unmanned boats and other small mobile platforms.

This paper “Low-cost and robust docking angle estimation for miniature USVs through the integration of camera and multi-zone ToF sensor” was published in Interdiscipline.
Huang J, Qian X, Li J, Jiang W. Low-cost and robust docking angle estimation for miniature USVs through the integration of camera and multi-zone ToF sensor. Interdiscipline 2026(1):0003, https://doi.org/10.55092/interdiscipline20260003.