CMAE-3D: Contrastive Masked AutoEncoders for Self-Supervised 3D Object Detection

LiDAR-based 3D object detection is a crucial task for autonomous driving, owing to its accurate object recognition and localization capabilities in the 3D real-world space. However, existing methods heavily rely on time-consuming and laborious large-scale labeled LiDAR data, posing a bottleneck for both performance improvement and practical applications. In this paper, we propose Contrastive Masked AutoEncoders for self-supervised 3D object detection, dubbed as CMAE-3D, which is a promising solution to effectively alleviate label dependency in 3D perception. Specifically, we integrate Contrastive Learning (CL) and Masked AutoEncoders (MAE) into one unified framework to fully utilize the complementary characteristics of global semantic representation and local spatial perception. Furthermore, from the perspective of MAE, we develop the Geometric-Semantic Hybrid Masking (GSHM) to selectively mask representative regions in point clouds with imbalanced foreground-background and uneven density distribution, and design the Multi-scale Latent Feature Reconstruction (MLFR) to capture high-level semantic features while mitigating the redundant reconstruction of low-level details. From the perspective of CL, we present Hierarchical Relational Contrastive Learning (HRCL) to mine rich semantic similarity information while alleviating the issue of negative sample mismatch from both the voxel-level and frame-level. Extensive experiments demonstrate the effectiveness of our pre-training method when applied to multiple mainstream 3D object detectors (SECOND, CenterPoint and PV-RCNN) on three popular datasets (KITTI, Waymo and nuScenes).