Unsupervised 3D Object Detection by Commonsense Clue.

Traditional 3D object detectors, whether fully-, semi-, or weakly-supervised, rely heavily on extensive human annotations. In contrast, this paper introduces an unsupervised 3D object detector that automatically discerns object patterns without such annotations. To achieve this, we propose a Commonsense Prototype-based Detector (CPD) for unsupervised 3D object detection. CPD first constructs Commonsense Prototypes (CProto) to represent the geometric center and size of objects. It then generates high-quality pseudo-labels and guides detector convergence using size and geometry priors from CProto. Building on CPD, we further introduce CPD++, an enhanced version that improves performance by leveraging motion cues. CPD++ learns localization from stationary objects and recognition from moving objects, facilitating the mutual transfer of localization and recognition knowledge between these two object types. Both CPD and CPD++ outperform existing state-of-the-art unsupervised 3D detectors. Furthermore, when trained on Waymo Open Dataset (WOD) and tested on KITTI, CPD++ achieves 89.25% 3D Average Precision (AP) on the moderate car class at a 0.5 IoU threshold, reaching 95.3% of the performance attained by fully supervised counterparts. These results underscore the significant advancements brought by our method.