Bird’s-Eye-View (BEV) building mapping from remote sensing images is a studying hotspot with broad applications. In recent years, deep learning has significantly advanced the development of automatic building extraction methods. However, most existing research focuses on segmenting buildings from a single perspective, such as orthophotos, overlooking the rich information of multi-view images. In surveying and mapping, individual building instances need to be separated even when they are adjacent or touching. Since orthophotos cannot capture building walls due to self-occlusion, distinguishing between closely connected buildings in densely built areas becomes challenging. To tackle this issue, we propose a multi-view collaborative pipeline for instance-level building segmentation. This pipeline utilizes a grouping optimization algorithm to merge segmentation results from multiple views, which are predicted by general instance segmentation networks and projected onto the BEV, to produce the final building instance polygons. Both qualitative and quantitative results show that the proposed multi-view collaborative pipeline significantly outperforms the popular orthophoto-based pipeline on theInstanceBuildingdataset.

Three-dimensional (3D) building models play a vital role in numerous applications including urban planning and smart cities. Recent 3D building modeling methods either rely heavily on available manaually-collected footprint reference or hardly reach real automation on par with manual editing. To approach the automated extraction of instance-level 3D buildings at Level of Detail (LoD) 1, we introduce an innovative end-to-end 3D building instance segmentation model. This model predicts accurate contours and heights of individual buildings simultaneously using ortho-rectified high-resolution remote sensing images and Digital Surface Models (DSMs), getting rid of additional reference data and impirical parameter settings. Firstly, we propose an Anchor-Free Multi-head building extraction network (AFM) tailored for extracting 2D building contours. AFM incorporates a full-resolution, long-range correlation boosted global mask prediction branch along with anchor-free bounding box generation, as well as a newly developed online hard sample mining (OHSM) training procedure based on uncertainty analysis to emphasize error-prone positions in locating building contours. Subsequently, we incorporate a height prediction component to AFM in order to derive accurate building height information, thus creating the comprehensive 3D building extraction model referred to as AFM-3D. The two-stage AFM-3D operates by initially predicting 3D cube proposals, followed by generating refined 3D prismatic models (LoD1 models) for each proposal. Thorough experimentation across different datasets demonstrates the superior performance of AFM and AFM-3D. A significant enhancement of 6.4% quality score is observed on the urban 3D dataset in comparison to recent methods. In addition to the proposed novel methodology, we compare anchor-based and anchor-free bounding box generation mechanisms for remote sensing data, explore pixel-based and contour-based segmentation strategies, evaluate learning-based and empirical height estimation methods, and discuss the indispensability of DSM data in 3D building instance extraction. These analyses yield valuable insights that contribute to the progression of 3D building extraction research.

Long-range dependency modeling has been widely considered in modern deep learning-based semantic segmentation methods, especially those designed for large-size remote sensing images, to compensate the intrinsic locality of standard convolutions. However, in previous studies, the long-range dependency, modeled with an attention mechanism or transformer model, has been based on unsupervised learning, instead of explicit supervision from the objective ground truth (GT). In this article, we propose a novel supervised long-range correlation method for land-cover classification, called the supervised long-range correlation network (SLCNet), which is shown to be superior to the currently used unsupervised strategies. In SLCNet, pixels sharing the same category are considered highly correlated and those having different categories are less relevant, which can be easily supervised by the category consistency information available in the GT semantic segmentation map. Under such supervision, the recalibrated features are more consistent for pixels of the same category and more discriminative for pixels of other categories, regardless of their proximity. To complement the detailed information lacking in the global long-range correlation, we introduce an auxiliary adaptive receptive field feature extraction (ARFE) module, parallel to the long-range correlation module in the encoder, to capture finely detailed feature representations for multisize objects in multiscale remote sensing images. In addition, we apply multiscale side-output supervision and a hybrid loss function as local and global constraints to further boost the segmentation accuracy. Experiments were conducted on three public remote sensing datasets (the ISPRS Vaihingen dataset, the ISPRS Potsdam dataset, and the DeepGlobe dataset). Compared with the advanced segmentation methods from the computer vision, medicine, and remote sensing communities, the proposed SLCNet method achieved state-of-the-art performance on all the datasets. The code will be made available at gpcv.whu.edu.cn/data.

Although the orientation and scale properties of the objects in remote sensing images have been widely considered in the modern deep learning-based object detection methods, the spatial distribution property of objects has rarely been investigated. There is a distinct spatial distribution difference between close-range objects and remote sensing objects: the former may exhibit extensive mutual occlusion and overlap, whereas the latter rarely overlap. A current remote sensing object detection algorithm that ignores the spatial distribution difference may unnecessarily apply the massive anchor-based proposal bounding box generation and nonmaximum suppression (NMS) operations. In this article, considering the unique spatial distribution of remote sensing objects, and also the other spatial properties, we propose a novel, compact, and spatial-oriented object detection framework for remote sensing images. The proposed two-stage convolutional neural network (CNN) framework, which we call the Remote-sensing Spatial Adaptation DETector (RSADet), considers the spatial distribution, scale, and orientation/shape varieties of the objects in remote sensing images. In the first stage, each object instance is inferred on the scale-attention boosted CNN heatmaps to generate candidate bounding boxes, instead of using the anchor-based proposal box generation and NMS. In the second stage, deformable convolutions are introduced to adapt to the geometric variations of different object instances and to avoid the impact of complex and changeable backgrounds. A new bounding box confidence (IoU score) prediction branch is introduced as a convenient constraint for eliminating unreliable boxes and improving performance. Experiments were conducted on a large single-class remote sensing object detection dataset (the Ningbo Pylon dataset) built as part of this study and an open-source extraordinarily large multiclass dataset (the object DetectIon in Optical Remote sensing image (DIOR) dataset). Compared with the advanced detectors from both the computer vision and remote sensing communities, the proposed RSADet achieved state-of-the-art performance on both datasets.

Detecting the terrain surface cracks caused by earthquakes, which are termed coseismic ruptures, has important significance for discovering concealed faults, monitoring their movements, and forecasting possible follow-on earthquakes. On May 22, 2021, Maduo County in Qinghai province, China, suffered an earthquake with a magnitude of 7.4, which created densely distributed cracks. In this study, we designed an automatic crack detection framework based on remote sensing technology. With the use of low-altitude unmanned aerial vehicles (UAVs), we obtained very high-resolution aerial images of the area affected by the earthquake, which were further processed by photogrammetric software to produce digital orthophoto maps (DOMs). We then designed a novel terrain surface crack detection neural network, which differs from the previous methods that focus on detecting cracks in man-made object surfaces such as flat roads. We investigated the spatial property of the sinuous linear cracks and handled this by introducing adaptive deformable convolutions with a context-channel-space boosted mechanism. The feature extraction stage, feature optimization stage, and upsampling stage were embedded with the deformable convolutions to form a compact and powerful crack detector, named Crack-CADNet (the Context-chAnnel-space boosted Deformable convolutional neural network for crack detection). The postprocessing included filtering out the nontectonic cracks, aided by annotations from experts, and grouping and vectorizing the generated binary segmentation map as crack polygons, which were evaluated at the instance level. In addition to the first in-depth investigation of detecting earthquake cracks with aerial remote sensing and a deep learning based process, the crack detection network we propose outperformed the recent convolutional neural network (CNN)-based methods designed for general semantic segmentation and crack detection. Source code and the Maduo earthquake crack dataset will be available at http://gpcv.whu.edu.cn/data/.