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Completeness and accuracy are two important factors in image-based indoor scene 3D reconstruction. Thus, an efficient image capturing scheme that could completely cover the scene, and a robust reconstruction method that could accurately reconstruct the scene are required. To this end, in this article we propose a new pipeline for indoor scene capturing and reconstruction using a mini drone and a ground robot, which takes both capturing completeness and reconstruction accuracy into consideration. First, we use a mini drone to capture aerial video of the indoor scene, from which a 3D aerial map is reconstructed. Then, the robot moving path is planned and a set of ground-view reference images are synthesized from the aerial map. After that, the robot enters the scene and captures ground video autonomously while using the reference images to locate its position during the movement. Finally, the ground and aerial images, which are adaptively extracted from the captured videos, are merged to reconstruct a complete and accurate indoor scene model. Experimental results on two indoor scenes demonstrate the effectiveness and robustness of our proposed indoor scene capturing and reconstruction pipeline.

In this paper, we present a simple yet effective rotation averaging pipeline, termed Incremental Rotation Averaging (IRA), which is inspired by the well-developed incremental Structure from Motion (SfM) techniques. Unlike the traditional rotation averaging methods which estimate all the absolute rotations simultaneously and focus on designing either robust loss function or outlier filtering strategy, here the absolute rotations are estimated in an incremental way. Similar to the incremental SfM, our IRA is robust to relative rotation outliers and could achieve accurate rotation averaging results. In addition, we propose several key techniques, such as initial triplet and Next-Best-View selection, Weighted Local/Global Optimization, and Re-Rotation Averaging, to push the rotation averaging results one step further. Ablation studies and comparison experiments on the 1DSfM, Campus, and San Francisco datasets demonstrate the effectiveness of our IRA and its advantages over the state-of-the-art rotation averaging methods in accuracy and robustness.

The titanium carbide phase was synthesized in laser melted-pool in situ as the reinforced particles of nickel based composite coating on Ti-6Al-4V alloy surface using the nickel and graphite blending powder by laser cladding. The microstructure investigation showed that the petals-shaped particles and granular particles were two main morphology of titanium carbide particles. And a few spiral-shaped titanium carbide pattern and eutectic titanium carbide appeared on the cross-sections of the coating. The spiral-shaped titanium carbide pattern composed of some slender arc-shape titanium carbide particles and the eutectic titanium carbide was fine. The morphology and distribution of the spiral-shaped titanium carbide patterns and eutectic titanium carbide confrmed that their growth mechanism was the dissolution-precipitation mechanism and was affected by the convection behavior of the laser melted pool. The spiral-shaped titanium carbide pattern would precipitate out the high-temperature melts under high-speed convection. The eutectic titanium carbide would precipitate out when the melts stopped convection or dropped to eutectic temperature.

The 3D digitalization and documentation of ancient Chinese architecture is challenging because of architectural complexity and structural delicacy. To generate complete and detailed models of this architecture, it is better to acquire, process, and fuse multi-source data instead of single-source data. In this paper, we describe our work on 3D digital preservation of ancient Chinese architecture based on multisource data. We first briefly introduce two surveyed ancient Chinese temples, Foguang Temple and Nanchan Temple. Then, we report the data acquisition equipment we used and the multi-source data we acquired. Finally, we provide an overview of several applications we conducted based on the acquired data, including ground and aerial image fusion, image and LiDAR (light detection and ranging) data fusion, and architectural scene surface reconstruction and semantic modeling. We believe that it is necessary to involve multi-source data for the 3D digital preservation of ancient Chinese architecture, and that the work in this paper will serve as a heuristic guideline for the related research communities. Keywords: Ancient Chinese architecture, 3D digital preservation, Multi-source data acquisition, Architectural scene modeling

Urban scene modeling is a challenging task for the photogrammetry and computer vision community due to its large scale, structural complexity, and topological delicacy. This paper presents an efficient multistep modeling framework for large-scale urban scenes from aerial images. It takes aerial images and a textured 3D mesh model generated by an image-based modeling system as the input and outputs compact polygon models with semantics at different levels of detail (LODs). Based on the key observation that urban buildings usually have piecewise planar rooftops and vertical walls, we propose a segment-based modeling method, which consists of three major stages: scene segmentation, roof contour extraction, and building modeling. By combining the deep neural network predictions with geometric constraints of the 3D mesh, the scene is first segmented into three classes. Then, for each building mesh, the 2D line segments are detected and used to slice the ground into polygon cells, followed by assigning each cell a roof plane via a MRF optimization. Finally, the LOD model is obtained by extruding cells to their corresponding planes. Compared with direct modeling in 3D space, we transform the mesh into a uniform 2D image grid representation and most of the modeling work is performed in 2D space, which has the advantages of low computational complexity and high robustness. In addition, our method doesn’t require any global prior, such as the Manhattan or Atlanta world assumption, making it flexible to model scenes with different characteristics and complexity. Experiments on both single buildings and large-scale urban scenes demonstrate that by combining 2D photometric with 3D geometric information, the proposed algorithm is robust and efficient in urban scene LOD vectorized modeling compared with the state-of-the-art approaches.

Purpose This paper aims to explore the influence of the reinforcement included either glass beads (GBs) or carbon fiber (CF) on the reinforced polyamide 12 (PA12) composite samples prepared by selective laser sintering (SLS). Design/methodology/approach In this paper, the microstructure and mechanical properties are investigated, and the results are compared with those obtained for non-reinforced pure PA12 samples prepared by SLS. Findings The tensile fracture surface of the non-reinforced pure PA12 sample presents strong micro-deformation within the crack origination zone between the melted PA12 matrix and the un-melted PA12 particle cores. As a result, the pure PA12 sample exhibits the greatest maximum elongation. The maximum tensile strength is obtained for the CF reinforced sample because of the strengthening effect of CF and the relatively good bonding between CFs and the PA12 matrix. The minimum tensile strength is obtained for the GB reinforced PA12 sample because of the relatively weak bonding between GBs and the PA12 matrix. Originality/value These results demonstrate that the characteristics of the interfaces between the reinforcement and the PA12 matrix have an important influence on the fracture mechanisms and mechanical properties of PA12 composites fabricated by SLS.

Herein, the effect of multilayer core–shell-structured Zn/ZnO/Al2O3 particles on thermal conductivity and dielectric properties of epoxy composites was investigated. The core–shell-structured Zn/ZnO particles were obtained by a simple calcination method, and the multilayer core–shell-structured Zn/ZnO/Al2O3 particles were prepared using hydrolysis process. The Zn/ZnO/Al2O3/epoxy composites were fabricated, and atomic force microscopy (AFM) images showed that the fillers were well distributed in epoxy matrix. Thermal conductivity of Zn/ZnO/Al2O3/epoxy composites increased 178% by adding 12.0 wt% of Zn/ZnO/Al2O3 particles. The dielectric constant of composites increased obviously with the increased content of Zn/ZnO/Al2O3 particles, while the dielectric loss is still low. These results illustrate that the combination of the thermal and dielectric properties tuned by multilayer core–shell particles gives potential application in extended domains for epoxy composites.

Ancient Chinese architecture 3D digitalization and documentation is a challenging task for the image based modeling community due to its architectural complexity and structural delicacy. Currently, an effective approach to ancient Chinese architecture 3D reconstruction is to merge the two point clouds, separately obtained from ground and aerial images by the SfM technique. There are two understanding issues should be specially addressed: (1) it is difficult to find the point matches between the images from different sources due to their remarkable variations in viewpoint and scale; (2) due to the inevitable drift phenomenon in any SfM reconstruction process, the resulting two point clouds are no longer strictly related by a single similarity transformation as it should be theoretically. To address these two issues, a new point cloud merging method is proposed in this work. Our method has the following characteristics: (1) the images are matched by leveraging sparse mesh based image synthesis; (2) the putative point matches are filtered by geometrical consistency check and geometrical model verification; and (3) the two point clouds are merged via bundle adjustment by linking the ground-to-aerial tracks. Extensive experiments show that our method outperforms many of the state-of-the-art approaches in terms of ground-to-aerial image matching and point cloud merging.

Mangrove forests are intertidal wetland with a diverse assemblage of trees, shrubs and palms growing along tropical and subtropical coastlines. Effective mapping of mangrove forests has not yet been achieved due to the periodicity of tidal dynamics. Our previous studies showed that a submerged mangrove recognition index (SMRI), which was proposed based on the differential spectral signature of mangrove forests from high and low tides, has potential advantages in mangrove discrimination and classification. However, the effect of tide level on the performance of SMRI is still unclear. In this study, GaoFen-1 images with various tide heights were acquired, and SMRI images from low tide to high tide were obtained. Then, the resulting SMRI images were compared in detail, and the relationship between tide level and SMRI values was analyzed. This experiment was accomplished via a case study in Yunlin, Guangxi Province in China. The results showed that an increased difference in tide level led to an increase in the number of pixels of high SMRI values, indicating that more undetected submerged mangrove forests could be distinguished using SMRI. Furthermore, an exponential relationship was observed between SMRI and tide level. It suggests that SMRI effectively helps to distinguish submerged mangrove forests from multi-tide remotely-sensed imagery, and also benefits accurate mapping of mangrove forests.

Designing and controlling the interface interaction between polymer and filler is a challenge for nanocomposite insulation materials with the enhanced insulating and thermal conductive properties simultaneously. Meanwhile, the roles of the interface in the charge distribution of the composite on the macroscale are well studied. However, the effects of the interface on the nanoscale are not clear. In this work, first, we have demonstrated a method to modify the dielectric constant of composites by introduced air into the core-shell-structured M-SiO2@Al2O3 particles. To clarify the electric interfacial region, we use Kelvin probe force microscopy (KPFM) to image with high spatial resolution of the surface charge distribution around an individual M-SiO2@Al2O3 particle embedded in the epoxy matrix. We find that the KPFM results of the distinct electric interfacial region are consistent with the finite element simulation. Moreover, the charge accumulation is much easier in the presence of the M-SiO2@Al2O3 particles because of the increasing concentration of traps. This work provides significant insight into understanding the intrinsic interfacial behavior in insulating polymeric composites.

Image based modeling and laser scanning are two commonly used approaches in large-scale architectural scene reconstruction nowadays. In order to generate a complete scene reconstruction, an effective way is to completely cover the scene using ground and aerial images, supplemented by laser scanning on certain regions with low texture and complicated structure. Thus, the key issue is to accurately calibrate cameras and register laser scans in a unified framework. To this end, we proposed a three-step pipeline for complete scene reconstruction by merging images and laser scans. First, images are captured around the architecture in a multi-view and multi-scale way and are feed into a structure-from-motion (SfM) pipeline to generate SfM points. Then, based on the SfM result, the laser scanning locations are automatically planned by considering textural richness, structural complexity of the scene and spatial layout of the laser scans. Finally, the images and laser scans are accurately merged in a coarse-to-fine manner. Experimental evaluations on two ancient Chinese architecture datasets demonstrate the effectiveness of our proposed complete scene reconstruction pipeline., Comment: This manuscript has been accepted by IEEE TCSVT

From the theory of damage mechanics, based on the Hoek-Brown strength criterion and Weibull distribution law of rock microelement strength, a statistical constitutive model of rock thermal damage is established by using equivalent strain hypothesis, and the theoretical model is modified by considering the compression coefficient and residual strength correction coefficient. The rationality of the modified model is verified by experimental data. The results show that the stress-strain curves of rock can be divided into four stages: initial compaction, stable damage propagation, damage strengthening expansion, and damage failure according to the characteristics of rock damage evolution. The peak stress of rock increases exponentially with the increase of confining pressure, and the maximum damage evolution rate decreases exponentially with the increase of confining pressure, which indicates that confining pressure delays the development of cumulative damage. The peak stress and maximum damage evolution rate of rock decrease exponentially with the increase of temperature, which accelerates the damage of rock. The initial damage of rock is thermal damage caused by temperature, and the damage value increases with the increase of temperature. The revised theoretical curve reflects the characteristics of rock compaction stage and residual strength and improves the coincidence with the experimental curve. The research results provide a reference for the establishment of thermal damage constitutive model of rock in deep engineering.

To improve the wear resistance of gray cast iron and the quality of the laser cladding coating, a composite coating was designed and produced using Cu-Ti-Ni blending powder on the surface of gray cast iron by fiber laser cladding system. The phase constituents and microstructure of the composite coating were investigated using X-ray diffraction (XRD) and scanning electron micrograph (SEM). Microhardness and wear resistance of the coatings were evaluated. The experimental results indicated that TiC reinforced composite coating was produced and the matrix of the laser cladding zone composed of alloy γ-Fe, acicular martensite, and α-Cu. Microscale TiC particles were synthesized in the laser melted pool using the graphite phase of the substrate and the titanium atom of the blending powder. The surface properties of gray cast iron was improved by TiC reinforced comppsite coating. The microhardness of the laser cladding zone was approximately 2 to 3 times that of the substrate and the wear resistance of the coating was significantly improved. The wear mechanism of the coating was adhesive wear and abrasive wear because the matrix was soft alloy γ-Fe and α-Cu. The coating could significantly improve the performance of grey cast iron under severe service conditions.

In the present study, Fe–Cr–Ni alloy coatings were produced by laser cladding using the blending powder of Cr and Ni on the surface of T10 steel. The composition of phase and microstructure were analyzed by scanning electron microscope (SEM) and x-ray diffraction (XRD). The microhardness and corrosion resistance were investigated. The Fe–Cr–Ni cladding coatings composed of austenites and a few eutectic ferrites. And the content of eutectic ferrite in the grain boundary decreased with the decreasing Cr/Ni ratio of the blending powder. The Creq/Nieq ratio and the ferrite number (FN) of the coatings confirm that the solidification process was the AF mode for the Fe–Cr–Ni cladding coatings. The average microhardness value of Fe–Cr–Ni coatings was about 380HV0.2 and the Cr/Ni ratio of the blending powder was not an obvious effect. The corrosion resistance of Fe–Cr–Ni alloy coatings which was significantly superior to T10 steel decreased with the decreasing Cr/Ni ratio of the blending powder. This research exhibits that the Fe–Cr–Ni coatings and laser cladding processing have a potential engineering application value on hypereutectoid carbon steel.