MS3D++: Ensemble of Experts for Multi-Source Unsupervised Domain Adaptation in 3D Object Detection (2308.05988v2)

Abstract: Deploying 3D detectors in unfamiliar domains has been demonstrated to result in a significant 70-90% drop in detection rate due to variations in lidar, geography, or weather from their training dataset. This domain gap leads to missing detections for densely observed objects, misaligned confidence scores, and increased high-confidence false positives, rendering the detector highly unreliable. To address this, we introduce MS3D++, a self-training framework for multi-source unsupervised domain adaptation in 3D object detection. MS3D++ generates high-quality pseudo-labels, allowing 3D detectors to achieve high performance on a range of lidar types, regardless of their density. Our approach effectively fuses predictions of an ensemble of multi-frame pre-trained detectors from different source domains to improve domain generalization. We subsequently refine predictions temporally to ensure temporal consistency in box localization and object classification. Furthermore, we present an in-depth study into the performance and idiosyncrasies of various 3D detector components in a cross-domain context, providing valuable insights for improved cross-domain detector ensembling. Experimental results on Waymo, nuScenes and Lyft demonstrate that detectors trained with MS3D++ pseudo-labels achieve state-of-the-art performance, comparable to training with human-annotated labels in Bird's Eye View (BEV) evaluation for both low and high density lidar. Code is available at https://github.com/darrenjkt/MS3D

Overview of MS3D++: Ensemble of Experts for Multi-Source Unsupervised Domain Adaptation in 3D Object Detection

The paper presents MS3D++, an innovative framework for multi-source unsupervised domain adaptation (UDA) tailored for 3D object detection in autonomous driving setups. This framework addresses the substantial domain gap often observed when deploying 3D detectors across different lidar setups, geographical locations, and varying weather conditions—a gap that can lead to a decline in detection performance by as much as 70-90%. Such domain disparities typically manifest in missed detections, misaligned confidence scores, and increased false positives.

Key Contributions

1. High-Quality Pseudo-Label Generation: MS3D++ initiates a self-training procedure by generating high-quality pseudo-labels, enabling effective domain adaptation for a broad spectrum of lidar types, irrespective of their density. This approach circumvents the unreliability in confidence scores caused by domain shifts while maintaining robust object localization and classification.
2. Detector Ensembling and Temporal Refinement: The framework harnesses the potential of an ensemble of pre-trained detectors from varied source domains, coupled with temporal refinement, to mitigate the domain gaps. By fusing predictions from these detectors and refining them over time, MS3D++ ensures consistency in the spatiotemporal dimension, enhancing the accuracy of object detection.
3. Quantitative Analysis of Detector Components: Through comprehensive cross-domain evaluations, the paper provides insights into the performance differences of various 3D detector components. This analysis is pivotal for understanding how different architectures and detection strategies perform when applied to unfamiliar domains, thereby guiding effective ensemble configurations.
4. State-of-the-Art Performance: Empirical results across prominent lidar datasets—Waymo, nuScenes, and Lyft—demonstrate that detectors trained with MS3D++ consistently achieve state-of-the-art performance. Notably, these results are on par with, and sometimes exceed, those obtained from models trained with human-annotated data. This achievement underscores the framework's capability to replace costly manual labeling with automated pseudo-labeling, thereby reducing overhead and accelerating the deployment of autonomous systems.

Numerical Results and Implications

The experimental evaluation highlights MS3D++'s ability to significantly boost detection accuracy—specifically achieving notable improvements in both BEV and 3D average precision metrics. For instance, detectors trained on pseudo-labels derived from MS3D++ outperform conventional state-of-the-art models by leveraging multi-source domain knowledge through effective ensembling.

The theoretical and practical implications of this work are profound. Theoretically, it provides a paradigm shift towards leveraging diverse data sources for domain adaptation in 3D perception tasks. Practically, MS3D++ paves the way for enhanced autonomous driving systems that can operate reliably across diverse environments without requiring exhaustive domain-specific annotations.

Future Directions

Looking ahead, further exploration could involve integrating multi-modal data to enhance pseudo-labeling robustness. Moreover, expanding the framework to incorporate active learning could refine pseudo-label quality by prioritizing human intervention on uncertain detections. These enhancements could further optimize MS3D++ for real-world applications, continually advancing the frontiers of autonomous perception technologies.

In conclusion, MS3D++ represents a significant advancement in unsupervised domain adaptation for 3D object detection, mitigating domain shift challenges through an ensemble of expert detectors and temporal refinement. Its potential to eliminate dependencies on manually annotated data marks a pivotal step toward scalable and adaptable autonomous systems.