Vision-Centric Bird-Eye-View (BEV) perception has shown promising potential and attracted increasing attention in autonomous driving. Recent works mainly focus on improving efficiency or accuracy but neglect the domain shift problem, resulting in severe degradation of transfer performance. With extensive observations, we figure out the significant domain gaps existing in the scene, weather, and day-night changing scenarios and make the first attempt to solve the domain adaption problem for multi-view 3D object detection. Since BEV perception approaches are usually complicated and contain several components, the domain shift accumulation on multi-latent spaces makes BEV domain adaptation challenging. In this paper, we propose a novel Multi-level Multi-space Alignment Teacher-Student ($M^{2}ATS$) framework to ease the domain shift accumulation, which consists of a Depth-Aware Teacher (DAT) and a Multi-space Feature Aligned (MFA) student model. Specifically, DAT model adopts uncertainty guidance to sample reliable depth information in target domain. After constructing domain-invariant BEV perception, it then transfers pixel and instance-level knowledge to student model. To further alleviate the domain shift at the global level, MFA student model is introduced to align task-relevant multi-space features of two domains. To verify the effectiveness of $M^{2}ATS$, we conduct BEV 3D object detection experiments on four cross domain scenarios and achieve state-of-the-art performance (e.g., +12.6% NDS and +9.1% mAP on Day-Night). Code and dataset will be released.

神经形态尖峰摄像机以生物启发的方式生成具有高时间分辨率的数据流，该方式在自动驾驶等现实世界应用中具有巨大的潜力。与RGB流相反，Spike流具有克服运动模糊的固有优势，从而导致对高速对象的更准确的深度估计。但是，几乎不可能以监督的方式培训尖峰深度估计网络，因为获得时间密集的尖峰流的配对深度标签非常费力和挑战。在本文中，我们没有构建带有完整深度标签的Spike流数据集，而是以不受监督的方式从开源RGB数据集（例如Kitti）和估算峰值深度转移知识。此类问题的关键挑战在于RGB和SPIKE模式之间的模态差距，以及标记的源RGB和未标记的目标尖峰域之间的域间隙。为了克服这些挑战，我们引入了无监督的尖峰深度估计的跨模式跨域（BICROSS）框架。我们的方法通过引入中介模拟的源尖峰域来缩小源RGB和目标尖峰之间的巨大差距。要具体而言，对于跨模式阶段，我们提出了一种新颖的粗到精细知识蒸馏（CFKD），将图像和像素级知识从源RGB转移到源尖峰。这种设计分别利用了RGB和SPIKE模式的大量语义和密集的时间信息。对于跨域阶段，我们引入了不确定性引导的均值老师（UGMT），以生成具有不确定性估计的可靠伪标签，从而减轻了源尖峰和目标尖峰域之间的变化。此外，我们提出了一种全局级特征对齐方法（GLFA），以对齐两个域之间的特征并生成更可靠的伪标签。

最近，检测变压器（DETR）是一种端到端对象检测管道，已达到有希望的性能。但是，它需要大规模标记的数据，并遭受域移位，尤其是当目标域中没有标记的数据时。为了解决这个问题，我们根据平均教师框架MTTRANS提出了一个端到端的跨域检测变压器，该变压器可以通过伪标签充分利用对象检测训练中未标记的目标域数据和在域之间的传输知识中的传输知识。我们进一步提出了综合的多级特征对齐方式，以改善由平均教师框架生成的伪标签，利用跨尺度的自我注意事项机制在可变形的DETR中。图像和对象特征在本地，全局和实例级别与基于域查询的特征对齐（DQFA），基于BI级的基于图形的原型对齐（BGPA）和Wine-Wise图像特征对齐（TIFA）对齐。另一方面，未标记的目标域数据伪标记，可用于平均教师框架的对象检测训练，可以导致更好的特征提取和对齐。因此，可以根据变压器的架构对迭代和相互优化的平均教师框架和全面的多层次特征对齐。广泛的实验表明，我们提出的方法在三个领域适应方案中实现了最先进的性能，尤其是SIM10K到CityScapes方案的结果，从52.6地图提高到57.9地图。代码将发布。

Domain adaptive object detection (DAOD) aims to alleviate transfer performance degradation caused by the cross-domain discrepancy. However, most existing DAOD methods are dominated by computationally intensive two-stage detectors, which are not the first choice for industrial applications. In this paper, we propose a novel semi-supervised domain adaptive YOLO (SSDA-YOLO) based method to improve cross-domain detection performance by integrating the compact one-stage detector YOLOv5 with domain adaptation. Specifically, we adapt the knowledge distillation framework with the Mean Teacher model to assist the student model in obtaining instance-level features of the unlabeled target domain. We also utilize the scene style transfer to cross-generate pseudo images in different domains for remedying image-level differences. In addition, an intuitive consistency loss is proposed to further align cross-domain predictions. We evaluate our proposed SSDA-YOLO on public benchmarks including PascalVOC, Clipart1k, Cityscapes, and Foggy Cityscapes. Moreover, to verify its generalization, we conduct experiments on yawning detection datasets collected from various classrooms. The results show considerable improvements of our method in these DAOD tasks. Our code is available on \url{https://github.com/hnuzhy/SSDA-YOLO}.

我们解决对象检测中的域适应问题，其中在源（带有监控）和目标域（没有监督的域的域名）之间存在显着的域移位。作为广泛采用的域适应方法，自培训教师学生框架（学生模型从教师模型生成的伪标签学习）在目标域中产生了显着的精度增益。然而，由于其偏向源域，它仍然存在从教师产生的大量低质量伪标签（例如，误报）。为了解决这个问题，我们提出了一种叫做自适应无偏见教师（AUT）的自我训练框架，利用对抗的对抗学习和弱强的数据增强来解决域名。具体而言，我们在学生模型中使用特征级的对抗性培训，确保从源和目标域中提取的功能共享类似的统计数据。这使学生模型能够捕获域不变的功能。此外，我们在目标领域的教师模型和两个域上的学生模型之间应用了弱强的增强和相互学习。这使得教师模型能够从学生模型中逐渐受益，而不会遭受域移位。我们展示了AUT通过大边距显示所有现有方法甚至Oracle（完全监督）模型的优势。例如，我们在有雾的城市景观（Clipart1k）上实现了50.9％（49.3％）地图，分别比以前的最先进和甲骨文高9.2％（5.2％）和8.2％（11.0％）

在本文中，我们提出了激光雷达蒸馏，以弥合由不同的激光束引起的3D对象检测的域间隙。在许多现实世界中，大规模生产的机器人和车辆使用的激光点通常比大型公共数据集的光束少。此外，随着LIDARS升级到具有不同光束量的其他产品模型，使用先前版本的高分辨率传感器捕获的标记数据变得具有挑战性。尽管域自适应3D检测最近取得了进展，但大多数方法都难以消除梁诱导的域间隙。我们发现，在训练过程中，必须将源域的点云密度与目标域的点云密度保持一致。受到这一发现的启发，我们提出了一个渐进式框架，以减轻光束诱导的域移位。在每次迭代中，我们首先通过下采样高光束点云来产生低光束伪激光雷达。然后，使用教师学生的框架来将丰富的信息从数据中提取更多的信息。 Waymo，Nuscenes和Kitti数据集的大量实验具有三个不同的基于激光雷达的探测器，这证明了我们激光蒸馏的有效性。值得注意的是，我们的方法不会增加推理的任何额外计算成本。

When facing changing environments in the real world, the lightweight model on client devices suffers from severe performance drops under distribution shifts. The main limitations of the existing device model lie in (1) unable to update due to the computation limit of the device, (2) the limited generalization ability of the lightweight model. Meanwhile, recent large models have shown strong generalization capability on the cloud while they can not be deployed on client devices due to poor computation constraints. To enable the device model to deal with changing environments, we propose a new learning paradigm of Cloud-Device Collaborative Continual Adaptation, which encourages collaboration between cloud and device and improves the generalization of the device model. Based on this paradigm, we further propose an Uncertainty-based Visual Prompt Adapted (U-VPA) teacher-student model to transfer the generalization capability of the large model on the cloud to the device model. Specifically, we first design the Uncertainty Guided Sampling (UGS) to screen out challenging data continuously and transmit the most out-of-distribution samples from the device to the cloud. Then we propose a Visual Prompt Learning Strategy with Uncertainty guided updating (VPLU) to specifically deal with the selected samples with more distribution shifts. We transmit the visual prompts to the device and concatenate them with the incoming data to pull the device testing distribution closer to the cloud training distribution. We conduct extensive experiments on two object detection datasets with continually changing environments. Our proposed U-VPA teacher-student framework outperforms previous state-of-the-art test time adaptation and device-cloud collaboration methods. The code and datasets will be released.

Recently, Bird's-Eye-View (BEV) representation has gained increasing attention in multi-view 3D object detection, which has demonstrated promising applications in autonomous driving. Although multi-view camera systems can be deployed at low cost, the lack of depth information makes current approaches adopt large models for good performance. Therefore, it is essential to improve the efficiency of BEV 3D object detection. Knowledge Distillation (KD) is one of the most practical techniques to train efficient yet accurate models. However, BEV KD is still under-explored to the best of our knowledge. Different from image classification tasks, BEV 3D object detection approaches are more complicated and consist of several components. In this paper, we propose a unified framework named BEV-LGKD to transfer the knowledge in the teacher-student manner. However, directly applying the teacher-student paradigm to BEV features fails to achieve satisfying results due to heavy background information in RGB cameras. To solve this problem, we propose to leverage the localization advantage of LiDAR points. Specifically, we transform the LiDAR points to BEV space and generate the foreground mask and view-dependent mask for the teacher-student paradigm. It is to be noted that our method only uses LiDAR points to guide the KD between RGB models. As the quality of depth estimation is crucial for BEV perception, we further introduce depth distillation to our framework. Our unified framework is simple yet effective and achieves a significant performance boost. Code will be released.

Deep learning has achieved notable success in 3D object detection with the advent of large-scale point cloud datasets. However, severe performance degradation in the past trained classes, i.e., catastrophic forgetting, still remains a critical issue for real-world deployment when the number of classes is unknown or may vary. Moreover, existing 3D class-incremental detection methods are developed for the single-domain scenario, which fail when encountering domain shift caused by different datasets, varying environments, etc. In this paper, we identify the unexplored yet valuable scenario, i.e., class-incremental learning under domain shift, and propose a novel 3D domain adaptive class-incremental object detection framework, DA-CIL, in which we design a novel dual-domain copy-paste augmentation method to construct multiple augmented domains for diversifying training distributions, thereby facilitating gradual domain adaptation. Then, multi-level consistency is explored to facilitate dual-teacher knowledge distillation from different domains for domain adaptive class-incremental learning. Extensive experiments on various datasets demonstrate the effectiveness of the proposed method over baselines in the domain adaptive class-incremental learning scenario.

Bird's-Eye-View (BEV) 3D Object Detection is a crucial multi-view technique for autonomous driving systems. Recently, plenty of works are proposed, following a similar paradigm consisting of three essential components, i.e., camera feature extraction, BEV feature construction, and task heads. Among the three components, BEV feature construction is BEV-specific compared with 2D tasks. Existing methods aggregate the multi-view camera features to the flattened grid in order to construct the BEV feature. However, flattening the BEV space along the height dimension fails to emphasize the informative features of different heights. For example, the barrier is located at a low height while the truck is located at a high height. In this paper, we propose a novel method named BEV Slice Attention Network (BEV-SAN) for exploiting the intrinsic characteristics of different heights. Instead of flattening the BEV space, we first sample along the height dimension to build the global and local BEV slices. Then, the features of BEV slices are aggregated from the camera features and merged by the attention mechanism. Finally, we fuse the merged local and global BEV features by a transformer to generate the final feature map for task heads. The purpose of local BEV slices is to emphasize informative heights. In order to find them, we further propose a LiDAR-guided sampling strategy to leverage the statistical distribution of LiDAR to determine the heights of local slices. Compared with uniform sampling, LiDAR-guided sampling can determine more informative heights. We conduct detailed experiments to demonstrate the effectiveness of BEV-SAN. Code will be released.

通过新兴的大规模自动驾驶数据集和深度学习技术的快速发展，单眼3D对象检测（MONO3D）取得了巨大的改进。但是，由于严重的域间隙（例如，视野（FOV），像素大小和数据集中的对象大小）引起的，MONO3D检测器的泛化难度，导致对看不见的域的性能急剧下降。为了解决这些问题，我们将位置不变的变换和多尺度训练与像素大小的深度策略相结合，以构建有效的统一摄像机将军（CGP）。它充分考虑了不同摄像机捕获的图像的FOV和像素大小的差异。此外，当通过详尽的系统研究交叉描述时，我们进一步研究了定量指标的障碍。我们发现预测的大小偏见会导致巨大的失败。因此，我们提出了2d-3d几何符合对象缩放策略（GCO），以通过实例级级增强来弥合差距。我们称为DGMono3D的方法在所有评估的数据集上都能达到出色的性能，并且即使没有在目标域上使用数据，也超过了无监督域的适应方案。

To achieve accurate and low-cost 3D object detection, existing methods propose to benefit camera-based multi-view detectors with spatial cues provided by the LiDAR modality, e.g., dense depth supervision and bird-eye-view (BEV) feature distillation. However, they directly conduct point-to-point mimicking from LiDAR to camera, which neglects the inner-geometry of foreground targets and suffers from the modal gap between 2D-3D features. In this paper, we propose the learning scheme of Target Inner-Geometry from the LiDAR modality into camera-based BEV detectors for both dense depth and BEV features, termed as TiG-BEV. First, we introduce an inner-depth supervision module to learn the low-level relative depth relations between different foreground pixels. This enables the camera-based detector to better understand the object-wise spatial structures. Second, we design an inner-feature BEV distillation module to imitate the high-level semantics of different keypoints within foreground targets. To further alleviate the BEV feature gap between two modalities, we adopt both inter-channel and inter-keypoint distillation for feature-similarity modeling. With our target inner-geometry distillation, TiG-BEV can effectively boost BEVDepth by +2.3% NDS and +2.4% mAP, along with BEVDet by +9.1% NDS and +10.3% mAP on nuScenes val set. Code will be available at https://github.com/ADLab3Ds/TiG-BEV.

域自适应对象检测（DAOD）旨在改善探测和测试数据来自不同域时的探测器的泛化能力。考虑到显着的域间隙，一些典型方法，例如基于Conscangan的方法，采用中间域来逐步地桥接源域和靶域。然而，基于Conscangan的中间域缺少对象检测的PIX或实例级监控，这导致语义差异。为了解决这个问题，在本文中，我们介绍了具有四种不同的低频滤波器操作的频谱增强一致性（FSAC）框架。通过这种方式，我们可以获得一系列增强数据作为中间域。具体地，我们提出了一种两级优化框架。在第一阶段，我们利用所有原始和增强的源数据来训练对象检测器。在第二阶段，采用增强源和目标数据，具有伪标签来执行预测一致性的自培训。使用均值优化的教师模型用于进一步修改伪标签。在实验中，我们分别评估了我们在单一和复合目标DAOD上的方法，这证明了我们方法的有效性。

Domain adaptation aims to bridge the domain shifts between the source and the target domain. These shifts may span different dimensions such as fog, rainfall, etc. However, recent methods typically do not consider explicit prior knowledge about the domain shifts on a specific dimension, thus leading to less desired adaptation performance. In this paper, we study a practical setting called Specific Domain Adaptation (SDA) that aligns the source and target domains in a demanded-specific dimension. Within this setting, we observe the intra-domain gap induced by different domainness (i.e., numerical magnitudes of domain shifts in this dimension) is crucial when adapting to a specific domain. To address the problem, we propose a novel Self-Adversarial Disentangling (SAD) framework. In particular, given a specific dimension, we first enrich the source domain by introducing a domainness creator with providing additional supervisory signals. Guided by the created domainness, we design a self-adversarial regularizer and two loss functions to jointly disentangle the latent representations into domainness-specific and domainness-invariant features, thus mitigating the intra-domain gap. Our method can be easily taken as a plug-and-play framework and does not introduce any extra costs in the inference time. We achieve consistent improvements over state-of-the-art methods in both object detection and semantic segmentation.

Domain adaptation for Cross-LiDAR 3D detection is challenging due to the large gap on the raw data representation with disparate point densities and point arrangements. By exploring domain-invariant 3D geometric characteristics and motion patterns, we present an unsupervised domain adaptation method that overcomes above difficulties. First, we propose the Spatial Geometry Alignment module to extract similar 3D shape geometric features of the same object class to align two domains, while eliminating the effect of distinct point distributions. Second, we present Temporal Motion Alignment module to utilize motion features in sequential frames of data to match two domains. Prototypes generated from two modules are incorporated into the pseudo-label reweighting procedure and contribute to our effective self-training framework for the target domain. Extensive experiments show that our method achieves state-of-the-art performance on cross-device datasets, especially for the datasets with large gaps captured by mechanical scanning LiDARs and solid-state LiDARs in various scenes. Project homepage is at https://github.com/4DVLab/CL3D.git

While deep learning methods hitherto have achieved considerable success in medical image segmentation, they are still hampered by two limitations: (i) reliance on large-scale well-labeled datasets, which are difficult to curate due to the expert-driven and time-consuming nature of pixel-level annotations in clinical practices, and (ii) failure to generalize from one domain to another, especially when the target domain is a different modality with severe domain shifts. Recent unsupervised domain adaptation~(UDA) techniques leverage abundant labeled source data together with unlabeled target data to reduce the domain gap, but these methods degrade significantly with limited source annotations. In this study, we address this underexplored UDA problem, investigating a challenging but valuable realistic scenario, where the source domain not only exhibits domain shift~w.r.t. the target domain but also suffers from label scarcity. In this regard, we propose a novel and generic framework called ``Label-Efficient Unsupervised Domain Adaptation"~(LE-UDA). In LE-UDA, we construct self-ensembling consistency for knowledge transfer between both domains, as well as a self-ensembling adversarial learning module to achieve better feature alignment for UDA. To assess the effectiveness of our method, we conduct extensive experiments on two different tasks for cross-modality segmentation between MRI and CT images. Experimental results demonstrate that the proposed LE-UDA can efficiently leverage limited source labels to improve cross-domain segmentation performance, outperforming state-of-the-art UDA approaches in the literature. Code is available at: https://github.com/jacobzhaoziyuan/LE-UDA.

Domain adaptive detection aims to improve the generalization of detectors on target domain. To reduce discrepancy in feature distributions between two domains, recent approaches achieve domain adaption through feature alignment in different granularities via adversarial learning. However, they neglect the relationship between multiple granularities and different features in alignment, degrading detection. Addressing this, we introduce a unified multi-granularity alignment (MGA)-based detection framework for domain-invariant feature learning. The key is to encode the dependencies across different granularities including pixel-, instance-, and category-levels simultaneously to align two domains. Specifically, based on pixel-level features, we first develop an omni-scale gated fusion (OSGF) module to aggregate discriminative representations of instances with scale-aware convolutions, leading to robust multi-scale detection. Besides, we introduce multi-granularity discriminators to identify where, either source or target domains, different granularities of samples come from. Note that, MGA not only leverages instance discriminability in different categories but also exploits category consistency between two domains for detection. Furthermore, we present an adaptive exponential moving average (AEMA) strategy that explores model assessments for model update to improve pseudo labels and alleviate local misalignment problem, boosting detection robustness. Extensive experiments on multiple domain adaption scenarios validate the superiority of MGA over other approaches on FCOS and Faster R-CNN detectors. Code will be released at https://github.com/tiankongzhang/MGA.

检测变压器最近显示出有希望的对象检测结果，并引起了越来越多的注意力。但是，如何开发有效的域适应技术来改善其跨域性能，尚不清楚和不清楚。在本文中，我们深入研究了这个主题，并从经验上发现，CNN骨架上的直接特征分布对齐仅带来有限的改进，因为它不能保证变压器中的域不变序列特征进行预测。为了解决这个问题，我们提出了一种新型的序列特征比对（SFA）方法，该方法是专门设计用于适应检测变压器的。从技术上讲，SFA由基于域查询的特征对齐（DQFA）模块和令牌特征对齐（TDA）模块组成。在DQFA中，一个新的域查询用于从两个域的令牌序列中汇总和对齐全局上下文。 DQFA分别在变压器编码器和解码器中部署时，降低了全局特征表示和对象关系中的域差异。同时，TDA在两个域中的序列中都对准令牌特征，从而分别降低了变压器编码器和解码器中局部和实例级特征表示中的域间隙。此外，提出了一种新型的两分匹配损失，以增强可鲁棒对象检测的特征可区分性。在三个具有挑战性的基准上进行的实验表明，SFA优于最先进的域自适应对象检测方法。代码已在以下网址提供：https：//github.com/encounter1997/sfa。

DETR风格的检测器在内域场景中脱颖而出，但是它们在域移位设置中的属性却没有探索。本文旨在根据两个发现，在域移位设置上使用DETR式检测器建立一个简单但有效的基线。首先，减轻主链的域移动，解码器输出功能在获得有利的结果方面表现出色。对于另一种高级域对准方法，这两个部分都进一步增强了性能。因此，我们提出了对象感知的对准（OAA）模块和最佳基于运输的比对（OTA）模块，以在骨干和检测器的输出上实现全面的域对齐。 OAA模块将伪标签标识的前景区域对齐骨干输出中的伪标签，从而导致基于域的不变特征。 OTA模块利用切成薄片的Wasserstein距离来最大化位置信息的保留，同时最大程度地减少解码器输出中的域间隙。我们将调查结果和对齐模块实施到我们的适应方法中，并基准在域移位设置上基于DETR风格的检测器。在各种领域自适应场景上进行的实验验证了我们方法的有效性。

在鸟眼中学习强大的表现（BEV），以进行感知任务，这是趋势和吸引行业和学术界的广泛关注。大多数自动驾驶算法的常规方法在正面或透视视图中执行检测，细分，跟踪等。随着传感器配置变得越来越复杂，从不同的传感器中集成了多源信息，并在统一视图中代表功能至关重要。 BEV感知继承了几个优势，因为代表BEV中的周围场景是直观和融合友好的。对于BEV中的代表对象，对于随后的模块，如计划和/或控制是最可取的。 BEV感知的核心问题在于（a）如何通过从透视视图到BEV来通过视图转换来重建丢失的3D信息； （b）如何在BEV网格中获取地面真理注释； （c）如何制定管道以合并来自不同来源和视图的特征； （d）如何适应和概括算法作为传感器配置在不同情况下各不相同。在这项调查中，我们回顾了有关BEV感知的最新工作，并对不同解决方案进行了深入的分析。此外，还描述了该行业的BEV方法的几种系统设计。此外，我们推出了一套完整的实用指南，以提高BEV感知任务的性能，包括相机，激光雷达和融合输入。最后，我们指出了该领域的未来研究指示。我们希望该报告能阐明社区，并鼓励对BEV感知的更多研究。我们保留一个活跃的存储库来收集最新的工作，并在https://github.com/openperceptionx/bevperception-survey-recipe上提供一包技巧的工具箱。