3D点云的卷积经过广泛研究，但在几何深度学习中却远非完美。卷积的传统智慧在3D点之间表现出特征对应关系，这是对差的独特特征学习的内在限制。在本文中，我们提出了自适应图卷积（AGCONV），以供点云分析的广泛应用。 AGCONV根据其动态学习的功能生成自适应核。与使用固定/各向同性核的解决方案相比，AGCONV提高了点云卷积的灵活性，有效，精确地捕获了不同语义部位的点之间的不同关系。与流行的注意力体重方案不同，AGCONV实现了卷积操作内部的适应性，而不是简单地将不同的权重分配给相邻点。广泛的评估清楚地表明，我们的方法优于各种基准数据集中的点云分类和分割的最新方法。同时，AGCONV可以灵活地采用更多的点云分析方法来提高其性能。为了验证其灵活性和有效性，我们探索了基于AGCONV的完成，DeNoing，Upsmpling，注册和圆圈提取的范式，它们与竞争对手相当甚至优越。我们的代码可在https://github.com/hrzhou2/adaptconv-master上找到。

Point cloud learning has lately attracted increasing attention due to its wide applications in many areas, such as computer vision, autonomous driving, and robotics. As a dominating technique in AI, deep learning has been successfully used to solve various 2D vision problems. However, deep learning on point clouds is still in its infancy due to the unique challenges faced by the processing of point clouds with deep neural networks. Recently, deep learning on point clouds has become even thriving, with numerous methods being proposed to address different problems in this area. To stimulate future research, this paper presents a comprehensive review of recent progress in deep learning methods for point clouds. It covers three major tasks, including 3D shape classification, 3D object detection and tracking, and 3D point cloud segmentation. It also presents comparative results on several publicly available datasets, together with insightful observations and inspiring future research directions.

卷积神经网络（CNNS）在2D计算机视觉中取得了很大的突破。然而，它们的不规则结构使得难以在网格上直接利用CNNS的潜力。细分表面提供分层多分辨率结构，其中闭合的2 - 歧管三角网格中的每个面正恰好邻近三个面。本文推出了这两种观察，介绍了具有环形细分序列连接的3D三角形网格的创新和多功能CNN框架。在2D图像中的网格面和像素之间进行类比允许我们呈现网状卷积操作者以聚合附近面的局部特征。通过利用面部街区，这种卷积可以支持标准的2D卷积网络概念，例如，可变内核大小，步幅和扩张。基于多分辨率层次结构，我们利用汇集层，将四个面均匀地合并成一个和上采样方法，该方法将一个面分为四个。因此，许多流行的2D CNN架构可以容易地适应处理3D网格。可以通过自我参数化来回收具有任意连接的网格，以使循环细分序列连接，使子变量是一般的方法。广泛的评估和各种应用展示了SubDIVNet的有效性和效率。

Deep neural networks have enjoyed remarkable success for various vision tasks, however it remains challenging to apply CNNs to domains lacking a regular underlying structures such as 3D point clouds. Towards this we propose a novel convolutional architecture, termed Spi-derCNN, to efficiently extract geometric features from point clouds. Spi-derCNN is comprised of units called SpiderConv, which extend convolutional operations from regular grids to irregular point sets that can be embedded in R n , by parametrizing a family of convolutional filters. We design the filter as a product of a simple step function that captures local geodesic information and a Taylor polynomial that ensures the expressiveness. SpiderCNN inherits the multi-scale hierarchical architecture from classical CNNs, which allows it to extract semantic deep features. Experiments on ModelNet40[4] demonstrate that SpiderCNN achieves state-of-the-art accuracy 92.4% on standard benchmarks, and shows competitive performance on segmentation task.

Point cloud is an important type of geometric data structure. Due to its irregular format, most researchers transform such data to regular 3D voxel grids or collections of images. This, however, renders data unnecessarily voluminous and causes issues. In this paper, we design a novel type of neural network that directly consumes point clouds, which well respects the permutation invariance of points in the input. Our network, named PointNet, provides a unified architecture for applications ranging from object classification, part segmentation, to scene semantic parsing. Though simple, PointNet is highly efficient and effective. Empirically, it shows strong performance on par or even better than state of the art. Theoretically, we provide analysis towards understanding of what the network has learnt and why the network is robust with respect to input perturbation and corruption.

我们提出CPT：卷积点变压器 - 一种用于处理3D点云数据的非结构化性质的新型深度学习架构。 CPT是对现有关注的卷曲神经网络以及以前的3D点云处理变压器的改进。由于其在创建基于新颖的基于注意力的点集合嵌入通过制作用于处理动态局部点设定的邻域的卷积投影层的嵌入来实现这一壮举。结果点设置嵌入对输入点的排列是强大的。我们的小说CPT块在网络结构中通过动态图计算获得的本地邻居构建。它是完全可差异的，可以像卷积层一样堆叠，以学习点的全局属性。我们评估我们的模型在ModelNet40，ShapEnet​​部分分割和S3DIS 3D室内场景语义分割数据集等标准基准数据集上，以显示我们的模型可以用作各种点云处理任务的有效骨干，与现有状态相比 - 艺术方法。

基于简单的扩散层对空间通信非常有效的洞察力，我们对3D表面进行深度学习的新的通用方法。由此产生的网络是自动稳健的，以改变表面的分辨率和样品 - 一种对实际应用至关重要的基本属性。我们的网络可以在各种几何表示上离散化，例如三角网格或点云，甚至可以在一个表示上培训然后应用于另一个表示。我们优化扩散的空间支持，作为连续网络参数，从纯粹的本地到完全全球范围，从而消除手动选择邻域大小的负担。该方法中唯一的其他成分是在每个点处独立地施加的多层的Perceptron，以及用于支持方向滤波器的空间梯度特征。由此产生的网络简单，坚固，高效。这里，我们主要专注于三角网格表面，并且展示了各种任务的最先进的结果，包括表面分类，分割和非刚性对应。

Unlike images which are represented in regular dense grids, 3D point clouds are irregular and unordered, hence applying convolution on them can be difficult. In this paper, we extend the dynamic filter to a new convolution operation, named PointConv. PointConv can be applied on point clouds to build deep convolutional networks. We treat convolution kernels as nonlinear functions of the local coordinates of 3D points comprised of weight and density functions. With respect to a given point, the weight functions are learned with multi-layer perceptron networks and density functions through kernel density estimation. The most important contribution of this work is a novel reformulation proposed for efficiently computing the weight functions, which allowed us to dramatically scale up the network and significantly improve its performance. The learned convolution kernel can be used to compute translation-invariant and permutation-invariant convolution on any point set in the 3D space. Besides, PointConv can also be used as deconvolution operators to propagate features from a subsampled point cloud back to its original resolution. Experiments on ModelNet40, ShapeNet, and ScanNet show that deep convolutional neural networks built on PointConv are able to achieve state-of-the-art on challenging semantic segmentation benchmarks on 3D point clouds. Besides, our experiments converting CIFAR-10 into a point cloud showed that networks built on PointConv can match the performance of convolutional networks in 2D images of a similar structure.

由于其高质量的对象表示和有效的获取方法，3D点云吸引了越来越多的架构，工程和构建的关注。因此，文献中已经提出了许多点云特征检测方法来自动化一些工作流，例如它们的分类或部分分割。然而，点云自动化系统的性能显着落后于图像对应物。尽管这种故障的一部分源于云云的不规则性，非结构性和混乱，这使得云特征检测的任务比图像一项更具挑战性，但我们认为，图像域缺乏灵感可能是主要的。这种差距的原因。确实，鉴于图像特征检测中卷积神经网络（CNN）的压倒性成功，设计其点云对应物似乎是合理的，但是所提出的方法都不类似于它们。具体而言，即使许多方法概括了点云中的卷积操作，但它们也无法模仿CNN的多种功能检测和汇总操作。因此，我们提出了一个基于图卷积的单元，称为收缩单元，可以垂直和水平堆叠，以设计类似CNN的3D点云提取器。鉴于点云中点之间的自我，局部和全局相关性传达了至关重要的空间几何信息，因此我们在特征提取过程中还利用它们。我们通过为ModelNet-10基准数据集设计功能提取器模型来评估我们的建议，并达到90.64％的分类精度，表明我们的创新想法是有效的。我们的代码可在github.com/albertotamajo/shrinking-unit上获得。

The irregular domain and lack of ordering make it challenging to design deep neural networks for point cloud processing. This paper presents a novel framework named Point Cloud Transformer(PCT) for point cloud learning. PCT is based on Transformer, which achieves huge success in natural language processing and displays great potential in image processing. It is inherently permutation invariant for processing a sequence of points, making it well-suited for point cloud learning. To better capture local context within the point cloud, we enhance input embedding with the support of farthest point sampling and nearest neighbor search. Extensive experiments demonstrate that the PCT achieves the state-of-the-art performance on shape classification, part segmentation, semantic segmentation and normal estimation tasks.

随着激光雷达传感器和3D视觉摄像头的扩散，3D点云分析近年来引起了重大关注。经过先驱工作点的成功后，基于深度学习的方法越来越多地应用于各种任务，包括3D点云分段和3D对象分类。在本文中，我们提出了一种新颖的3D点云学习网络，通过选择性地执行具有动态池的邻域特征聚合和注意机制来提出作为动态点特征聚合网络（DPFA-NET）。 DPFA-Net有两个可用于三维云的语义分割和分类的变体。作为DPFA-NET的核心模块，我们提出了一个特征聚合层，其中每个点的动态邻域的特征通过自我注意机制聚合。与其他分割模型相比，来自固定邻域的聚合特征，我们的方法可以在不同层中聚合来自不同邻居的特征，在不同层中为查询点提供更具选择性和更广泛的视图，并更多地关注本地邻域中的相关特征。此外，为了进一步提高所提出的语义分割模型的性能，我们提出了两种新方法，即两级BF-Net和BF-Rengralization来利用背景前台信息。实验结果表明，所提出的DPFA-Net在S3DIS数据集上实现了最先进的整体精度分数，在S3DIS数据集上进行了语义分割，并在不同的语义分割，部分分割和3D对象分类中提供始终如一的令人满意的性能。与其他方法相比，它也在计算上更有效。

我们提出了一种基于注意力的新型机制，可以学习用于点云处理任务的增强点特征，例如分类和分割。与先前的作品不同，该作品经过培训以优化预选的一组注意点的权重，我们的方法学会了找到最佳的注意点，以最大程度地提高特定任务的性能，例如点云分类。重要的是，我们主张使用单个注意点来促进语义理解在点特征学习中。具体而言，我们制定了一种新的简单卷积，该卷积结合了输入点及其相应学习的注意点或膝盖的卷积特征。我们的注意机制可以轻松地纳入最新的点云分类和分割网络中。对诸如ModelNet40，ShapenetPart和S3DIS之类的常见基准测试的广泛实验都表明，我们的支持LAP的网络始终优于各自的原始网络，以及其他竞争性替代方案，这些替代方案在我们的膝盖下采用了多个注意力框架。

Convolutional Neural Networks (CNNs) achieve impressive performance in a wide variety of fields. Their success benefited from a massive boost when very deep CNN models were able to be reliably trained. Despite their merits, CNNs fail to properly address problems with non-Euclidean data. To overcome this challenge, Graph Convolutional Networks (GCNs) build graphs to represent non-Euclidean data, borrow concepts from CNNs, and apply them in training. GCNs show promising results, but they are usually limited to very shallow models due to the vanishing gradient problem (see Figure 1). As a result, most state-of-the-art GCN models are no deeper than 3 or 4 layers. In this work, we present new ways to successfully train very deep GCNs. We do this by borrowing concepts from CNNs, specifically residual/dense connections and dilated convolutions, and adapting them to GCN architectures. Extensive experiments show the positive effect of these deep GCN frameworks. Finally, we use these new concepts to build a very deep 56-layer GCN, and show how it significantly boosts performance (+3.7% mIoU over state-of-the-art) in the task of point cloud semantic segmentation. We believe that the community can greatly benefit from this work, as it opens up many opportunities for advancing GCN-based research.

Point cloud completion is a generation and estimation issue derived from the partial point clouds, which plays a vital role in the applications in 3D computer vision. The progress of deep learning (DL) has impressively improved the capability and robustness of point cloud completion. However, the quality of completed point clouds is still needed to be further enhanced to meet the practical utilization. Therefore, this work aims to conduct a comprehensive survey on various methods, including point-based, convolution-based, graph-based, and generative model-based approaches, etc. And this survey summarizes the comparisons among these methods to provoke further research insights. Besides, this review sums up the commonly used datasets and illustrates the applications of point cloud completion. Eventually, we also discussed possible research trends in this promptly expanding field.

This paper presents SO-Net, a permutation invariant architecture for deep learning with orderless point clouds. The SO-Net models the spatial distribution of point cloud by building a Self-Organizing Map (SOM). Based on the SOM, SO-Net performs hierarchical feature extraction on individual points and SOM nodes, and ultimately represents the input point cloud by a single feature vector. The receptive field of the network can be systematically adjusted by conducting point-to-node k nearest neighbor search. In recognition tasks such as point cloud reconstruction, classification, object part segmentation and shape retrieval, our proposed network demonstrates performance that is similar with or better than state-of-the-art approaches. In addition, the training speed is significantly faster than existing point cloud recognition networks because of the parallelizability and simplicity of the proposed architecture. Our code is

通过当地地区的点特征聚合来捕获的细粒度几何是对象识别和场景理解在点云中的关键。然而，现有的卓越点云骨架通常包含最大/平均池用于局部特征聚集，这在很大程度上忽略了点的位置分布，导致细粒结构组装不足。为了缓解这一瓶颈，我们提出了一个有效的替代品，可以使用新颖的图形表示明确地模拟了本地点之间的空间关系，并以位置自适应方式聚合特征，从而实现位置敏感的表示聚合特征。具体而言，Papooling分别由两个关键步骤，图形结构和特征聚合组成，分别负责构造与将中心点连接的边缘与本地区域中的每个相邻点连接的曲线图组成，以将它们的相对位置信息映射到通道 - 明智的细心权重，以及基于通过图形卷积网络（GCN）的生成权重自适应地聚合局部点特征。 Papooling简单而且有效，并且足够灵活，可以随时为PointNet ++和DGCNN等不同的流行律源，作为即插即说运算符。关于各种任务的广泛实验，从3D形状分类，部分分段对场景分割良好的表明，伪装可以显着提高预测准确性，而具有最小的额外计算开销。代码将被释放。

Raw point clouds data inevitably contains outliers or noise through acquisition from 3D sensors or reconstruction algorithms. In this paper, we present a novel endto-end network for robust point clouds processing, named PointASNL, which can deal with point clouds with noise effectively. The key component in our approach is the adaptive sampling (AS) module. It first re-weights the neighbors around the initial sampled points from farthest point sampling (FPS), and then adaptively adjusts the sampled points beyond the entire point cloud. Our AS module can not only benefit the feature learning of point clouds, but also ease the biased effect of outliers. To further capture the neighbor and long-range dependencies of the sampled point, we proposed a local-nonlocal (L-NL) module inspired by the nonlocal operation. Such L-NL module enables the learning process insensitive to noise. Extensive experiments verify the robustness and superiority of our approach in point clouds processing tasks regardless of synthesis data, indoor data, and outdoor data with or without noise. Specifically, PointASNL achieves state-of-theart robust performance for classification and segmentation tasks on all datasets, and significantly outperforms previous methods on real-world outdoor SemanticKITTI dataset with considerate noise. Our code is released through https: //github.com/yanx27/PointASNL.

Many scientific fields study data with an underlying structure that is a non-Euclidean space. Some examples include social networks in computational social sciences, sensor networks in communications, functional networks in brain imaging, regulatory networks in genetics, and meshed surfaces in computer graphics. In many applications, such geometric data are large and complex (in the case of social networks, on the scale of billions), and are natural targets for machine learning techniques. In particular, we would like to use deep neural networks, which have recently proven to be powerful tools for a broad range of problems from computer vision, natural language processing, and audio analysis. However, these tools have been most successful on data with an underlying Euclidean or grid-like structure, and in cases where the invariances of these structures are built into networks used to model them.Geometric deep learning is an umbrella term for emerging techniques attempting to generalize (structured) deep neural models to non-Euclidean domains such as graphs and manifolds. The purpose of this paper is to overview different examples of geometric deep learning problems and present available solutions, key difficulties, applications, and future research directions in this nascent field.

Standard convolution is inherently limited for semantic segmentation of point cloud due to its isotropy about features. It neglects the structure of an object, results in poor object delineation and small spurious regions in the segmentation result. This paper proposes a novel graph attention convolution (GAC), whose kernels can be dynamically carved into specific shapes to adapt to the structure of an object. Specifically, by assigning proper attentional weights to different neighboring points, GAC is designed to selectively focus on the most relevant part of them according to their dynamically learned features. The shape of the convolution kernel is then determined by the learned distribution of the attentional weights. Though simple, GAC can capture the structured features of point clouds for finegrained segmentation and avoid feature contamination between objects. Theoretically, we provided a thorough analysis on the expressive capabilities of GAC to show how it can learn about the features of point clouds. Empirically, we evaluated the proposed GAC on challenging indoor and outdoor datasets and achieved the state-of-the-art results in both scenarios.