Spherical Criteria for Fast and Accurate 360° Object Detection

With the advance of omnidirectional panoramic technology, 360 • imagery has become increasingly popular in the past few years. To better understand the 360 • content, many works resort to the 360 • object detection and various criteria have been proposed to bound the objects and compute the intersection-over-union (IoU) between bounding boxes based on the common equirectangular projection (ERP) or perspective projection (PSP). However, the existing 360 • criteria are either inaccurate or inefficient for real-world scenarios. In this paper, we introduce a novel spherical criteria for fast and accurate 360 • object detection, including both spherical bounding boxes and spherical IoU (SphIoU). Based on the spherical criteria, we propose a novel two-stage 360 • detector, i.e., Reprojection R-CNN, by combining the advantages of both ERP and PSP, yielding efficient and accurate 360 • object detection. To validate the design of spherical criteria and Reprojection R-CNN, we construct two unbiased synthetic datasets for training and evaluation. Experimental results reveal that compared with the existing criteria, the two-stage detector with spherical criteria achieves the best mAP results under the same inference speed, demonstrating that the spherical criteria can be more suitable for 360 • object detection. Moreover, Reprojection R-CNN outperforms the previous state-of-theart methods by over 30% on mAP with competitive speed, which confirms the efficiency and accuracy of the design.