One-stage 3D object detection using mobile light detection and ranging (LiDAR) has developed rapidly in recent years. Specifically, one-stage methods have attracted attention because of their high efficiency and light weight compared with two-stage methods. Inspired by this, we present the semantic segmentation assisted one-stage three-dimensional vehicle object detection (SSA3D), a network for the rapid detection of objects that keeps the advantages of the semantic segmentation module in the two-stage methods without increasing redundant computational load. First, we modified the sampling of the farthest point to improve the quality of the sampling points. This helps to reduce sampling outlier points and bad points that are difficult to perceive in the spatial structure information surrounding the point. Second, a neighbor attention group module is devoted to selectively add extra weight to neighbor points because of the different importance of neighbor points for the corresponding sampling point. Correctly increasing the weight is helpful to obtain richer spatial structure information. Finally, a delicate box generation module is included as a voted center point layer based on the generalized Hoff vote method and an anchor-free regression. We used the feature aggregation module as the backbone and the feature propagation module as the auxiliary network to achieve efficiency. At the same time, the auxiliary network retains the ability to extract point-wise features from the state-of-the-art semantic segmentation network. In experiments, we evaluated and tested the SSA3D on a common KITTI dataset and achieved improved performance in the class of car accuracy.

The semantic segmentation of small objects in point clouds is currently one of the most demanding tasks in photogrammetry and remote sensing applications. Multi-resolution feature extraction and fusion can significantly enhance the ability of object classification and segmentation, so it is widely used in the image field. For this motivation, we propose a point cloud semantic segmentation network based on multi-scale feature fusion (MSSCN) to aggregate the feature of a point cloud with different densities and improve the performance of semantic segmentation. In our method, random downsampling is first applied to obtain point clouds of different densities. A Spatial Aggregation Net (SAN) is then employed as the backbone network to extract local features from these point clouds, followed by concatenation of the extracted feature descriptors at different scales. Finally, a loss function is used to combine the different semantic information from point clouds of different densities for network optimization. Experiments were conducted on the S3DIS and ScanNet datasets, and our MSSCN achieved accuracies of 89.80% and 86.3%, respectively, on these datasets. Our method showed better performance than the recent methods PointNet, PointNet++, PointCNN, PointSIFT, and SAN.

Semantic segmentation of 3D point clouds plays a vital role in autonomous driving, 3D maps, and smart cities, etc. Recent work such as PointSIFT shows that spatial structure information can improve the performance of semantic segmentation. Motivated by this phenomenon, we propose Spatial Aggregation Net (SAN) for point cloud semantic segmentation. SAN is based on multi-directional convolution scheme that utilizes the spatial structure information of point cloud. Firstly, Octant-Search is employed to capture the neighboring points around each sampled point. Secondly, we use multi-directional convolution to extract information from different directions of sampled points. Finally, max-pooling is used to aggregate information from different directions. The experimental results conducted on ScanNet database show that the proposed SAN has comparable results with state-of-the-art algorithms such as PointNet, PointNet++, and PointSIFT, etc. In particular, our method has better performance on flat, small objects, and the edge areas that connect objects. Moreover, our model has good trade-off in segmentation accuracy and time complexity.

Reconstructing building roofs from light detection and ranging (LiDAR) point clouds from aerial perspectives is significantly important in photogrammetry domains. This letter proposes a novel approach for three-dimensional (3D) real-world building roof reconstruction in Estonia, employing a two-stage self-supervised pre-training architecture to transform 3D roof point clouds into wireframe models. We utilize a self-supervised pre-training framework that incorporates a purpose-designed and efficient self-attention mechanism to generate point-wise features. Subsequently, we develop modules for corner detection and edge prediction to classify and regress the coordinates of corner points and determine optimal edge selections, respectively, to construct the final wireframe model. The effectiveness of our approach is evaluated on real-world roof datasets, achieving corner and edge precision accuracies of 83% and 78%, respectively. In addition, fine-tuning our self-supervised pre-training method with varying ratios of labeled data, particularly with only 50% partially labeled data, attains superior performance, achieving 84% and 85% corner and edge precision, respectively.

This study introduces an efficient approach for clustering roof wireframe vertices within the realm of model simplification based on a multiclass twin support vector machine (TWSVM) framework. The proposed method first assigns a dynamic label to each point of the input point cloud, and it then iteratively identifies k cluster center three-dimensional (3D) lines by maintaining short distances between wireframe candidate vertices sharing the same corner. In addition, it ensures that these wireframe candidates from one corner are distanced from the wireframe vertices from the other corners in a drafting roof dataset. This study extends the multiclass TWSVM to tackle the clustering problem of roof wireframe vertices, thus facilitating model simplification. Remarkably, this problem can be solved using a straightforward and efficient iterative algorithm. The results demonstrate that our proposed method achieves more accurate clustering results on 20 out of 24 roof wireframe vertex datasets compared to other relevant methods. Furthermore, the proposed method can efficiently and accurately extract the majority of vertices from roof wireframes in real-world Building3D dataset.