An Arbitrary-Oriented SAR Ship Detector Based on Offset Distance Representation and Weighted Rotation NMS

Compared to the horizontal bounding box (HBB), the oriented bounding box (OBB) exhibits substantial advantages in SAR ship detection owing to its outstanding ability to reflect the shape and orientation of ships. However, most OBB detectors are anchor-based, which not only requires the manual setting of numerous hyper-parameters but also increases the difficulty of network training and inference due to the introduction of angle information. Therefore, this paper proposes an anchor-free OBB detector to achieve arbitrary-oriented SAR ship detection. Specifically, the OBB is unified as a 6-distance representation related to each sample point, which is conducive to reducing the negative impact of measurement inconsistency on network training. Moreover, to boost the location accuracy of the ship, a neighborhood-weighted rotation non-maximum suppression method is presented to filter high-quality redundant boxes for corner coordinate weighting. Experiments on RBox-SSDD and HRSID illustrate that the proposed method outperforms some advanced arbitrary-oriented ship detectors.