Feature-Aligned Single-Stage Rotation Object Detection With Continuous Boundary

Recently, rotation detection has gained much attention and shown its potential for accurate localization in remote sensing scenes. However, the objects in remote sensing images have a variety of directions, sizes, and aspect ratios, which makes it difficult to locate and classify objects. Therefore, the object detection task is still facing great challenges in the field of remote sensing. In this article, we propose a novel single-stage detector, which includes feature alignment block (FAB), double regression branches (DRBs), and a circumcircle rotation box (CRB). FAB utilizes the deformable convolution to flexibly obtain the features of different aspect ratio objects and aligns the regression features with the corresponding classification features through fusion. Consequently, it can make the extracted feature information have stronger discrimination, which is conducive to improving the object position and classification accuracy. DRBs consist of a main regression branch and an auxiliary regression branch. The main regression branch is used to fine-tune the result of the auxiliary regression branch to obtain a more accurate regression result. Moreover, to eliminate the boundary discontinuity problem faced by regression-based detectors, we construct CRB through designing an angle of rotation and the radius of the circumcircle. Extensive experiments and visual analysis are conducted on three public benchmarks, i.e., DOTA, HRSC2016, and DIOR-R. The results show that our proposed method has excellent localization and classification performance for oriented objects on all the representative datasets.