OccluBEV: Occlusion Aware Spatiotemporal Modeling for Multi-view 3D Object Detection

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Abstract
Bird's-Eye-View (BEV) based 3D visual perception, which formulates a unified space for multi-view representation, has received wide attention in autonomous driving due to its scalability for downstream tasks. However, view transform in transformer-based BEV methods is agnostic of 3D occlusion relationships, resulting in model degradation. To construct a higher-quality BEV space, this paper analyzes the mutual occlusion problems in the view transform process and proposes a new transformer-based method named OccluBEV. OccluBEV alleviates the occlusion issue via point cloud information distillation in both the image and BEV space. Specifically, in the image space, we perform depth estimation for each pixel and utilize it to guide image feature mapping. Further, since predicting depth directly from monocular image is ill-posed, ignoring stereo information such as multi-view and temporal cues, this paper introduces a voxel visibility segmentation task in 3D BEV space. The task explicitly predicts whether each voxel in the 3D BEV grid is occupied or not. In addition, to alleviate the overfitting problem in BEV feature learning under a single task, we design a multi-head learning framework which jointly models multiple strongly-correlated tasks in a unified BEV space. The effectiveness of the proposed method is fully validated on the nuScenes dataset, achieving a competetive NDS/mAP score of 57.5/47.9 on the nuScenes test leaderboard using ResNet101 backbone, which is superior to state-of-the-art camera-based solutions.