  Semi-Supervised Object Detection (SSOD), aiming to explore unlabeled data for
boosting object detectors, has become an active task in recent years. However,
existing SSOD approaches mainly focus on horizontal objects, leaving
multi-oriented objects that are common in aerial images unexplored. This paper
proposes a novel Semi-supervised Oriented Object Detection model, termed SOOD,
built upon the mainstream pseudo-labeling framework. Towards oriented objects
in aerial scenes, we design two loss functions to provide better supervision.
Focusing on the orientations of objects, the first loss regularizes the
consistency between each pseudo-label-prediction pair (includes a prediction
and its corresponding pseudo label) with adaptive weights based on their
orientation gap. Focusing on the layout of an image, the second loss
regularizes the similarity and explicitly builds the many-to-many relation
between the sets of pseudo-labels and predictions. Such a global consistency
constraint can further boost semi-supervised learning. Our experiments show
that when trained with the two proposed losses, SOOD surpasses the
state-of-the-art SSOD methods under various settings on the DOTA-v1.5
benchmark. The code will be available at https://github.com/HamPerdredes/SOOD.
