Vehicle positioning is critical for inter-vehicle communication, navigation, vehicle monitoring and tracking. They are regarded as the core technology ensuring safety in everyday-driving. This paper proposes an enhanc...Vehicle positioning is critical for inter-vehicle communication, navigation, vehicle monitoring and tracking. They are regarded as the core technology ensuring safety in everyday-driving. This paper proposes an enhanced vehicle ego-localization method based on streetscape image database. It is most useful in the global positioning system(GPS) blind area. Firstly, a database is built by collecting streetscape images, extracting dominant color feature and detecting speeded up robust feature(SURF) points. Secondly, an image that the vehicle shoots at one point is analyzed to find a matching image in the database by dynamic programming(DP)matching. According to the image similarity, several images with higher probabilities are selected to realize coarse positioning. Finally, different weights are set to the coordinates of the shooting location with the maximum similarity and its 8 neighborhoods according to the number of matching points, and then interpolating calculation is applied to complete accurate positioning. Experimental results show that the accuracy of this study is less than 1.5 m and its running time is about 3.6 s. These are basically in line with the practical need. The described system has an advantage of low cost, high reliability and strong resistance to signal interference, so it has a better practical value as compared with visual odometry(VO) and radio frequency identification(RFID) based approach for vehicle positioning in the case of GPS not working.展开更多
Dense matching of remote sensing images is a key step in the generation of accurate digital surface models.The semi-global matching algorithm comprehensively considers the advantages and disadvantages of local matchin...Dense matching of remote sensing images is a key step in the generation of accurate digital surface models.The semi-global matching algorithm comprehensively considers the advantages and disadvantages of local matching and global matching in terms of matching effect and computational efficiency,so it is widely used in close-range,aerial and satellite image matching.Based on the analysis of the original semi-global matching algorithm,this paper proposes a semi-global high-resolution remote sensing image that takes into account the geometric constraints of the connection points and the image texture information based on a large amount of high-resolution remote sensing image data and the characteristics of clear image texture.123123The method includes 4 parts:①Precise orientation.Aiming at the system error in the image orientation model,the system error of the rational function model is compensated by the geometric constraint relationship of the connecting points between the images,and the sub-pixel positioning accuracy is obtained;②Epipolar image generation.After the original image is divided into blocks,the epipolar image is generated based on the projection trajectory method;③Image dense matching.In order to reduce the size of the cost space and calculation time,the image is pyramided and then semi-globally matched layer by layer.In the matching process,the disparity map expansion and erosion algorithm that takes into account the image texture information is introduced to restrict the disparity search range and better retain the edge characteristics of the ground objects;④Generate DSM.In order to test the matching effect,the weighted median filter algorithm is used to filter the disparity map,and the DSM is obtained based on the principle of forward intersection.Finally,the paper uses the matching results of WordView3 and Ziyuan No.3 stereo image to verify the effectiveness of this method.展开更多
Hollow cathode,with the highest plasma density,current density,and temperature,becomes one of the most important components in the electro-thruster system.As the electric-propulsion thruster performance is directly re...Hollow cathode,with the highest plasma density,current density,and temperature,becomes one of the most important components in the electro-thruster system.As the electric-propulsion thruster performance is directly related to the ionization rate,reliability,and lifetime of the hollow cathode,this paper develops a global model to study the effects of discharge current,gas flow rate,and gas species on the discharge characteristics in the insert and orifice regions of the hollow cathode.The emitter wall temperatures of hollow cathodes predicted by the global model are compared with experimental results from NSTAR thruster neutralization cathodes,confirming the model's validity.The influence of hollow cathode emitter material and structure sizes on the plasma parameters in the internal regions was also evaluated.The simulation results show that there is an optimal matching relationship between the discharge current and gas flow rate to guarantee the maximum ionization rate.The optimal working region for the hollow cathode has been deter-mined under different energetic,regime and structural parameters.The global model established in this paper can quickly determine the key structure and operating parameters of hollow cathode at the design stage,and provide the theoretical basis for hollow cathode design and development.展开更多
基金the National Natural Science Foundation of China(No.51278058)111 Project on Information of Vehicle-Infrastructure Sensing and ITS(No.B14043)+1 种基金the Natural Science Basic Research Program of Shaanxi Province,China(No.2018JQ6091)the Special Fund for Basic Scientific Research of Central Colleges,Chang’an University in China(Nos.310824150012,310824130248,310824141003,310824153103,310824151033,310824164004,300102328204 and 2014G1241046)
文摘Vehicle positioning is critical for inter-vehicle communication, navigation, vehicle monitoring and tracking. They are regarded as the core technology ensuring safety in everyday-driving. This paper proposes an enhanced vehicle ego-localization method based on streetscape image database. It is most useful in the global positioning system(GPS) blind area. Firstly, a database is built by collecting streetscape images, extracting dominant color feature and detecting speeded up robust feature(SURF) points. Secondly, an image that the vehicle shoots at one point is analyzed to find a matching image in the database by dynamic programming(DP)matching. According to the image similarity, several images with higher probabilities are selected to realize coarse positioning. Finally, different weights are set to the coordinates of the shooting location with the maximum similarity and its 8 neighborhoods according to the number of matching points, and then interpolating calculation is applied to complete accurate positioning. Experimental results show that the accuracy of this study is less than 1.5 m and its running time is about 3.6 s. These are basically in line with the practical need. The described system has an advantage of low cost, high reliability and strong resistance to signal interference, so it has a better practical value as compared with visual odometry(VO) and radio frequency identification(RFID) based approach for vehicle positioning in the case of GPS not working.
基金National Natural Science Foundation of China(41871367)Ministry of Science and Technology of the People’s Republic of China(2018YFE0206100)。
文摘Dense matching of remote sensing images is a key step in the generation of accurate digital surface models.The semi-global matching algorithm comprehensively considers the advantages and disadvantages of local matching and global matching in terms of matching effect and computational efficiency,so it is widely used in close-range,aerial and satellite image matching.Based on the analysis of the original semi-global matching algorithm,this paper proposes a semi-global high-resolution remote sensing image that takes into account the geometric constraints of the connection points and the image texture information based on a large amount of high-resolution remote sensing image data and the characteristics of clear image texture.123123The method includes 4 parts:①Precise orientation.Aiming at the system error in the image orientation model,the system error of the rational function model is compensated by the geometric constraint relationship of the connecting points between the images,and the sub-pixel positioning accuracy is obtained;②Epipolar image generation.After the original image is divided into blocks,the epipolar image is generated based on the projection trajectory method;③Image dense matching.In order to reduce the size of the cost space and calculation time,the image is pyramided and then semi-globally matched layer by layer.In the matching process,the disparity map expansion and erosion algorithm that takes into account the image texture information is introduced to restrict the disparity search range and better retain the edge characteristics of the ground objects;④Generate DSM.In order to test the matching effect,the weighted median filter algorithm is used to filter the disparity map,and the DSM is obtained based on the principle of forward intersection.Finally,the paper uses the matching results of WordView3 and Ziyuan No.3 stereo image to verify the effectiveness of this method.
基金supported by the National Natural Science Foundation of China (Nos.U22B20120,NSFC52202460 and NSFC52177128)the National Key R&D Program of China (Nos.2020YFC2201100 and 2021YFC2202804,2022YFB3403504)+1 种基金the China Postdoctoral Science Foundation (Nos.2021M690392 and 2021TQ0036)the Advanced Space Propulsion Laboratory of BICE and Beijing Engineering Research Center of Efficient and Green Aerospace Propulsion Technology,China (No.LabASP-2021-04).
文摘Hollow cathode,with the highest plasma density,current density,and temperature,becomes one of the most important components in the electro-thruster system.As the electric-propulsion thruster performance is directly related to the ionization rate,reliability,and lifetime of the hollow cathode,this paper develops a global model to study the effects of discharge current,gas flow rate,and gas species on the discharge characteristics in the insert and orifice regions of the hollow cathode.The emitter wall temperatures of hollow cathodes predicted by the global model are compared with experimental results from NSTAR thruster neutralization cathodes,confirming the model's validity.The influence of hollow cathode emitter material and structure sizes on the plasma parameters in the internal regions was also evaluated.The simulation results show that there is an optimal matching relationship between the discharge current and gas flow rate to guarantee the maximum ionization rate.The optimal working region for the hollow cathode has been deter-mined under different energetic,regime and structural parameters.The global model established in this paper can quickly determine the key structure and operating parameters of hollow cathode at the design stage,and provide the theoretical basis for hollow cathode design and development.
