Existing 3D object detection suffers from expensive annotation costs and poor transferability to unknown data due to the domain gap, Unsupervised Domain Adaptation (UDA) aims to generalize detection models trained in labeled source domains to perform robustly on unexplored target domains, providing a promising solution for cross-domain 3D object detection. Although Self-Training (ST) based cross-domain 3D detection methods with the assistance of pseudo-labeling techniques have achieved remarkable progress, they still face the issue of low-quality pseudo-labels when there are significant domain disparities due to the absence of a process for feature distribution alignment. While Adversarial Learning (AL) based methods can effectively align the feature distributions of the source and target domains, the inability to obtain labels in the target domain forces the adoption of asymmetric optimization losses, resulting in a challenging issue of source domain bias. To overcome these limitations, we propose a novel unsupervised domain adaptation framework for 3D object detection via collaborating ST and AL, dubbed as STAL3D, unleashing the complementary advantages of pseudo labels and feature distribution alignment. Additionally, a Background Suppression Adversarial Learning (BS-AL) module and a Scale Filtering Module (SFM) are designed tailored for 3D cross-domain scenes, effectively alleviating the issues of the large proportion of background interference and source domain size bias. Our STAL3D achieves state-of-the-art performance on multiple cross-domain tasks and even surpasses the Oracle results on Waymo $\rightarrow$ KITTI and Waymo $\rightarrow$ KITTI-rain.

我们提出了一种能够在无监督领域适应中实现3D物体检测的框架，称为STAL3D，通过协作自训练和对抗学习利用伪标签和特征分布对齐的互补优势，并设计了面向3D跨域场景的背景抑制对抗学习模块和尺度过滤模块，有效减轻了大部分背景干扰和源域尺寸偏差的问题。在多个跨域任务上，我们的STAL3D实现了最先进的性能，甚至在Waymo到KITTI和Waymo到KITTI-rain任务上超过了Oracle结果。

STAL3D：基于协作自训练和对抗学习的3D物体检测无监督域自适应