In this paper, we investigate the problem of determining regions in 3D scene visible to some given viewpoints when obstacles are present in the scene. We assume that the obstacles are composed of some opaque objects w...In this paper, we investigate the problem of determining regions in 3D scene visible to some given viewpoints when obstacles are present in the scene. We assume that the obstacles are composed of some opaque objects with closed surfaces. The problem is formulated in an implicit framework where the obstacles are represented by a level set function. The visible and invisible regions of the given viewpoints are determined through an efficient implicit ray tracing technique. As an extension of our approach, we apply the multiview visibility estimation to an image-based modeling technique. The unknown scene geometry and multiview visibility information are incorporated into a variational energy functional. By minimizing the energy functional, the true scene geometry as well as the accurate visibility information of the multiple views can be recovered from a number of scene images. This makes it feasible to handle the visibility problem of multiple views by our approach when the true scene geometry is unknown.展开更多
We propose an automatic garment seam modeling framework to create a garment model with the seam structure from a single image. In order to achieve this, a marked seam image database and parametric seam models have bee...We propose an automatic garment seam modeling framework to create a garment model with the seam structure from a single image. In order to achieve this, a marked seam image database and parametric seam models have been set up. Given a real seam image, we first identify the type of the seam image based on our marked semn image database and the seam parameters are parsed automatically by our sewing thread estimation method. Second the seam initial model is generated through the pre-defined parametric seam models. A garment model with the seam structure is finally obtained based on the seam position infrmation which users have marked on the garment. Moreover. we verify the effectiveness of our method with numerous experiments.展开更多
This paper proposes a numerical three-dimensional(3D)mesoscopic approach based on the discrete element method combined with X-ray computed tomography(XCT)images to characterize the dynamic impact behavior of heterogen...This paper proposes a numerical three-dimensional(3D)mesoscopic approach based on the discrete element method combined with X-ray computed tomography(XCT)images to characterize the dynamic impact behavior of heterogeneous coal-rock(HCR).The dynamic impact loading in three directions was modelled to investigate the effects of the 3D meso-structure on the failure patterns and fracture mechanism,with different impact velocities.The XCT image-based discrete element model of HCR was calibrated through appropriate standard uniaxial compression tests.Numerical simulations were carried out to investigate how the breakage behaviors are affected by different loading directions with different impact velocities.The loading direction,input energy,and spatial distribution of the mineral phase had a remarkable influence on the failure patterns and load-carrying capacities.The shape of the gangue phase and the approximate location of the gangue interfaces are key parameters to consider when investigating the failure patterns and fracture mechanism of heterogeneous rock materials.The damage and fracture tended to propagate from the surfaces to the HCR interior.The gangue phase area contacting the loading wall,growth direction of the strong gangue interfaces,and loading directions greatly influenced the failure patterns of the heterogeneous rock materials.展开更多
The objective of this study is to systematically assess the influences of the larynopharyneal anatomical details on airflow and particle behaviors during exhalation by means of image-based modeling. A physiologically ...The objective of this study is to systematically assess the influences of the larynopharyneal anatomical details on airflow and particle behaviors during exhalation by means of image-based modeling. A physiologically realistic nose-throat airway was developed with medical images. Individual airway anatomy such as uvula, pharynx, and larynx were then isolated for examination by progressively simplifying this image-based model geometry. Low Reynolds number (LRN) k-w model and Langrangian tracking model were used to simulate the dynamics of airflow and particle transport for a wide range of exhalation conditions (4-45 L/min) and particle sizes (1 nm-1 μm). Results showed that pharyngeal anatomical details exerted a significant impact on breathing resistance and particle profiles. Abrupt pressure drop resulting from the uvula-related airway obstruction was observed. Even though the total deposition rate in the nasal airway is largely unaffected by the upstream effect, the local deposition patterns vary notably. Results of this study also indicate that the pressure drop appears to be an appropriate parameter to characterize the geometric variations for diffusive depositions. Inclusion of pressure drop (D0.5Q-0.62dp0.07) gives an improved correlation than using the conventional diffusion factor (D0.5Q﹣0.28).展开更多
The numerical simulation of internal features,such as inclusions and voids,is important to analyze their impact on the performance of composite materials.However,the complex geometries of internal features and the ind...The numerical simulation of internal features,such as inclusions and voids,is important to analyze their impact on the performance of composite materials.However,the complex geometries of internal features and the induced continuous-discontinuous(C-D)deformation fields are challenges to their numerical simulation.In this study,a 3D approach using a simple mesh to simulate irregular internal geometries is developed for the first time.With the help of a developed voxel crack model,image models that are efficient when recording complex geometries are directly imported into the simulation.Surface reconstructions,which are usually labor-intensive,are excluded from this approach.Moreover,using image models as the geometric input,image processing techniques are applied to detect material interfaces and develop contact pairs.Then,the C-D deformations of the complex internal features are directly calculated based on the numerical manifold method.The accuracy and convergence of the developed3D approach are examined based on multiple benchmarks.Successful 3D C-D simulation of sandstones with naturally formed complex microfeatures demonstrates the capability of the developed approach.展开更多
In some military application scenarios,Unmanned Aerial Vehicles(UAVs)need to perform missions with the assistance of on-board cameras when radar is not available and communication is interrupted,which brings challenge...In some military application scenarios,Unmanned Aerial Vehicles(UAVs)need to perform missions with the assistance of on-board cameras when radar is not available and communication is interrupted,which brings challenges for UAV autonomous navigation and collision avoidance.In this paper,an improved deep-reinforcement-learning algorithm,Deep Q-Network with a Faster R-CNN model and a Data Deposit Mechanism(FRDDM-DQN),is proposed.A Faster R-CNN model(FR)is introduced and optimized to obtain the ability to extract obstacle information from images,and a new replay memory Data Deposit Mechanism(DDM)is designed to train an agent with a better performance.During training,a two-part training approach is used to reduce the time spent on training as well as retraining when the scenario changes.In order to verify the performance of the proposed method,a series of experiments,including training experiments,test experiments,and typical episodes experiments,is conducted in a 3D simulation environment.Experimental results show that the agent trained by the proposed FRDDM-DQN has the ability to navigate autonomously and avoid collisions,and performs better compared to the FRDQN,FR-DDQN,FR-Dueling DQN,YOLO-based YDDM-DQN,and original FR outputbased FR-ODQN.展开更多
Clouds play an important role when synthesizing realistic images of outdoor scenes.The realistic display of clouds is therefore one of the important research topics in computer graphics.In order to display realistic c...Clouds play an important role when synthesizing realistic images of outdoor scenes.The realistic display of clouds is therefore one of the important research topics in computer graphics.In order to display realistic clouds,we need methods for modeling,rendering,and animating clouds realistically.It is also important to control the shapes and appearances of clouds to create certain visual effects.In this paper,we explain our efforts and research results to meet such requirements,together with related researches on the visual simulation of clouds.展开更多
Structure from motion (SfM) has been an active research area in computer vision for decades and numerous practical applications are benefiting from this research. While no previous work has tried to summarize the appl...Structure from motion (SfM) has been an active research area in computer vision for decades and numerous practical applications are benefiting from this research. While no previous work has tried to summarize the applications appearing in the literature, this paper deals with a comprehensive overview of recent applications of SfM by classifying them into 10 categories, namely augmented reality, autonomous navigation/guidance, motion capture, hand-eye calibration, image/video processing, image-based 3D modeling, remote sensing, image organization/browsing, segmentation and recognition, and military applications. The goal is to provide insights for researchers to position their work more appropriately in the context of existing techniques, and to perceive both new applications and relevant research problems.展开更多
Artistic augmentation of photographs with water droplets aims at generating aesthetic yet realistic images, and thus differs from traditional augmented reality in two aspects. One difference lies in the adoption of a ...Artistic augmentation of photographs with water droplets aims at generating aesthetic yet realistic images, and thus differs from traditional augmented reality in two aspects. One difference lies in the adoption of a new image as the environment map in order to render reflected or refracted effects on the surface of inserted water droplets. The other difference is in modeling of water droplets including hanging droplets and resting droplets. These differences raise two research challenges:(1) how to adjust the brightness and colors of the new environment map to maintain visual consistency between the new environment map and the original input image;(2) how to model hanging and resting droplets aesthetically. This paper proposes a framework that addresses these two challenges and demonstrates the effectiveness of our framework by generating example augmented images.展开更多
基金supported by the National Natural Science Foundation of China under Grant No.90920009the National High-Tech Research and Development 863 Program of China under Grant No.2009AA01Z323
文摘In this paper, we investigate the problem of determining regions in 3D scene visible to some given viewpoints when obstacles are present in the scene. We assume that the obstacles are composed of some opaque objects with closed surfaces. The problem is formulated in an implicit framework where the obstacles are represented by a level set function. The visible and invisible regions of the given viewpoints are determined through an efficient implicit ray tracing technique. As an extension of our approach, we apply the multiview visibility estimation to an image-based modeling technique. The unknown scene geometry and multiview visibility information are incorporated into a variational energy functional. By minimizing the energy functional, the true scene geometry as well as the accurate visibility information of the multiple views can be recovered from a number of scene images. This makes it feasible to handle the visibility problem of multiple views by our approach when the true scene geometry is unknown.
基金Supported in part by the National Basic Research Program of China (Grant No. 2004CB318000)the National High-Tech Research & Development Program of China (Grant Nos. 2006AA01Z301, 2006AA01Z302, 2007AA01Z336)Key Grant Project of Chinese Ministry of Education (Grant No. 103001)
基金This work was partially supported by the National Natural Science Foundation of China under Grant Nos. 61532003 and 61421003.
文摘We propose an automatic garment seam modeling framework to create a garment model with the seam structure from a single image. In order to achieve this, a marked seam image database and parametric seam models have been set up. Given a real seam image, we first identify the type of the seam image based on our marked semn image database and the seam parameters are parsed automatically by our sewing thread estimation method. Second the seam initial model is generated through the pre-defined parametric seam models. A garment model with the seam structure is finally obtained based on the seam position infrmation which users have marked on the garment. Moreover. we verify the effectiveness of our method with numerous experiments.
基金The authors gratefully acknowledge the financial support received from the China Postdoctoral Science Foundation(2018M630676)National Nature Science Foundation of China(Nos.51675521 and 51779224)+1 种基金Zhejiang Basic Public Welfare Research Program(No.LHZ19E090002)and Open Founda-tion of Shandong Province Key Laboratory of Mine Mechanical.Engineering(No.2019KLMM105).
文摘This paper proposes a numerical three-dimensional(3D)mesoscopic approach based on the discrete element method combined with X-ray computed tomography(XCT)images to characterize the dynamic impact behavior of heterogeneous coal-rock(HCR).The dynamic impact loading in three directions was modelled to investigate the effects of the 3D meso-structure on the failure patterns and fracture mechanism,with different impact velocities.The XCT image-based discrete element model of HCR was calibrated through appropriate standard uniaxial compression tests.Numerical simulations were carried out to investigate how the breakage behaviors are affected by different loading directions with different impact velocities.The loading direction,input energy,and spatial distribution of the mineral phase had a remarkable influence on the failure patterns and load-carrying capacities.The shape of the gangue phase and the approximate location of the gangue interfaces are key parameters to consider when investigating the failure patterns and fracture mechanism of heterogeneous rock materials.The damage and fracture tended to propagate from the surfaces to the HCR interior.The gangue phase area contacting the loading wall,growth direction of the strong gangue interfaces,and loading directions greatly influenced the failure patterns of the heterogeneous rock materials.
文摘The objective of this study is to systematically assess the influences of the larynopharyneal anatomical details on airflow and particle behaviors during exhalation by means of image-based modeling. A physiologically realistic nose-throat airway was developed with medical images. Individual airway anatomy such as uvula, pharynx, and larynx were then isolated for examination by progressively simplifying this image-based model geometry. Low Reynolds number (LRN) k-w model and Langrangian tracking model were used to simulate the dynamics of airflow and particle transport for a wide range of exhalation conditions (4-45 L/min) and particle sizes (1 nm-1 μm). Results showed that pharyngeal anatomical details exerted a significant impact on breathing resistance and particle profiles. Abrupt pressure drop resulting from the uvula-related airway obstruction was observed. Even though the total deposition rate in the nasal airway is largely unaffected by the upstream effect, the local deposition patterns vary notably. Results of this study also indicate that the pressure drop appears to be an appropriate parameter to characterize the geometric variations for diffusive depositions. Inclusion of pressure drop (D0.5Q-0.62dp0.07) gives an improved correlation than using the conventional diffusion factor (D0.5Q﹣0.28).
基金supported by the National Natural Science Foundation of China(Grant Nos.41807277,42172306,and U1965204)the Natural Science Foundation of Hebei Province(Grant No.D2019202440)。
文摘The numerical simulation of internal features,such as inclusions and voids,is important to analyze their impact on the performance of composite materials.However,the complex geometries of internal features and the induced continuous-discontinuous(C-D)deformation fields are challenges to their numerical simulation.In this study,a 3D approach using a simple mesh to simulate irregular internal geometries is developed for the first time.With the help of a developed voxel crack model,image models that are efficient when recording complex geometries are directly imported into the simulation.Surface reconstructions,which are usually labor-intensive,are excluded from this approach.Moreover,using image models as the geometric input,image processing techniques are applied to detect material interfaces and develop contact pairs.Then,the C-D deformations of the complex internal features are directly calculated based on the numerical manifold method.The accuracy and convergence of the developed3D approach are examined based on multiple benchmarks.Successful 3D C-D simulation of sandstones with naturally formed complex microfeatures demonstrates the capability of the developed approach.
文摘In some military application scenarios,Unmanned Aerial Vehicles(UAVs)need to perform missions with the assistance of on-board cameras when radar is not available and communication is interrupted,which brings challenges for UAV autonomous navigation and collision avoidance.In this paper,an improved deep-reinforcement-learning algorithm,Deep Q-Network with a Faster R-CNN model and a Data Deposit Mechanism(FRDDM-DQN),is proposed.A Faster R-CNN model(FR)is introduced and optimized to obtain the ability to extract obstacle information from images,and a new replay memory Data Deposit Mechanism(DDM)is designed to train an agent with a better performance.During training,a two-part training approach is used to reduce the time spent on training as well as retraining when the scenario changes.In order to verify the performance of the proposed method,a series of experiments,including training experiments,test experiments,and typical episodes experiments,is conducted in a 3D simulation environment.Experimental results show that the agent trained by the proposed FRDDM-DQN has the ability to navigate autonomously and avoid collisions,and performs better compared to the FRDQN,FR-DDQN,FR-Dueling DQN,YOLO-based YDDM-DQN,and original FR outputbased FR-ODQN.
文摘Clouds play an important role when synthesizing realistic images of outdoor scenes.The realistic display of clouds is therefore one of the important research topics in computer graphics.In order to display realistic clouds,we need methods for modeling,rendering,and animating clouds realistically.It is also important to control the shapes and appearances of clouds to create certain visual effects.In this paper,we explain our efforts and research results to meet such requirements,together with related researches on the visual simulation of clouds.
基金Project (No. 61070140) supported by the National Natural Science Foundation of China
文摘Structure from motion (SfM) has been an active research area in computer vision for decades and numerous practical applications are benefiting from this research. While no previous work has tried to summarize the applications appearing in the literature, this paper deals with a comprehensive overview of recent applications of SfM by classifying them into 10 categories, namely augmented reality, autonomous navigation/guidance, motion capture, hand-eye calibration, image/video processing, image-based 3D modeling, remote sensing, image organization/browsing, segmentation and recognition, and military applications. The goal is to provide insights for researchers to position their work more appropriately in the context of existing techniques, and to perceive both new applications and relevant research problems.
基金This work was supported by the National Natural Science Foundation of China under Grant Nos.61772463 and 61772440the Aeronautical Science Foundation of China under Grant No.20165168007the National Key Research and Development Program of China under Grant No.2018YFB1700900。
文摘Artistic augmentation of photographs with water droplets aims at generating aesthetic yet realistic images, and thus differs from traditional augmented reality in two aspects. One difference lies in the adoption of a new image as the environment map in order to render reflected or refracted effects on the surface of inserted water droplets. The other difference is in modeling of water droplets including hanging droplets and resting droplets. These differences raise two research challenges:(1) how to adjust the brightness and colors of the new environment map to maintain visual consistency between the new environment map and the original input image;(2) how to model hanging and resting droplets aesthetically. This paper proposes a framework that addresses these two challenges and demonstrates the effectiveness of our framework by generating example augmented images.