针对传统车牌特征提取及匹配不足,提出了基于尺度不变特征变换(Scale-invariant feature transform,SIFT)的车牌特征提取及(Best Bin First,BBF)匹配方法。通过构建车牌字符标准模板,采用SIFT算法提取标准模板和待检测车牌中每个字符的S...针对传统车牌特征提取及匹配不足,提出了基于尺度不变特征变换(Scale-invariant feature transform,SIFT)的车牌特征提取及(Best Bin First,BBF)匹配方法。通过构建车牌字符标准模板,采用SIFT算法提取标准模板和待检测车牌中每个字符的SIFT特征向量,主要包括车牌高斯差分(Difference of Gauss,DoG)空间极值点检测,去除边缘相应点和低对比点,确定特征向量的方向和生成车牌特征向量。利用BBF(Best Bin First)算法完成标准模板特征向量与待检测车牌特征向量匹配,并获取识别结果。最后给出实验分析,证明该算法的识别率。展开更多
This paper,using the data of three Cluster satellites,compares the observations of Bursty Bulk Flow (BBF) by single satellite with those by multi satellites.The results indicate that there exists remarkable difference...This paper,using the data of three Cluster satellites,compares the observations of Bursty Bulk Flow (BBF) by single satellite with those by multi satellites.The results indicate that there exists remarkable difference between observations of BBF by single satellite and multi satellites.The observations of BBF by a single satellite depend on its position relative to the flow channel.The difference is caused by the localization characteristics of fast flows in the plasma sheet,and can lead to diverging views about substorm and causal relations among substorm phenomena.展开更多
This paper using the dataset of BBFs (bursty bulk flows) observed by two Cluster satellites C1 and C4 studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time differenc...This paper using the dataset of BBFs (bursty bulk flows) observed by two Cluster satellites C1 and C4 studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time differences of most of BBFs observed by C1 and C4 are smaller than 60 s. The average onset time difference of BBFs of C1 and C4 is 68.5 s. The probabilities of onset time difference of BBFs of C1 and C4 larger than 30 60 90 and 120 s are respectively 55% 35% 27% and 23%. The largest onset time difference of BBFs of C1 and C4 decreases with the increase of earthward component of maximum velocities of BBFs. The onset time difference of BBFs of C1 and C4 results from the velocity inhomogeneity inside the flow channel of BBF which may be produced in propagation path and/or in source region of BBFs. Such a wide range of onset time difference of BBFs suggests that the velocity inhomogeneity inside the flow channel of BBF is various. These results are very important to the current study of substorm research based on THEMIS data because they indicate that it is impossible to determine the onset time of BBF with a single satellite.展开更多
基金The Higher Education Teaching Reform Research Project of Chongqing Province in 2015,China(152072)~~
文摘针对传统车牌特征提取及匹配不足,提出了基于尺度不变特征变换(Scale-invariant feature transform,SIFT)的车牌特征提取及(Best Bin First,BBF)匹配方法。通过构建车牌字符标准模板,采用SIFT算法提取标准模板和待检测车牌中每个字符的SIFT特征向量,主要包括车牌高斯差分(Difference of Gauss,DoG)空间极值点检测,去除边缘相应点和低对比点,确定特征向量的方向和生成车牌特征向量。利用BBF(Best Bin First)算法完成标准模板特征向量与待检测车牌特征向量匹配,并获取识别结果。最后给出实验分析,证明该算法的识别率。
文摘This paper,using the data of three Cluster satellites,compares the observations of Bursty Bulk Flow (BBF) by single satellite with those by multi satellites.The results indicate that there exists remarkable difference between observations of BBF by single satellite and multi satellites.The observations of BBF by a single satellite depend on its position relative to the flow channel.The difference is caused by the localization characteristics of fast flows in the plasma sheet,and can lead to diverging views about substorm and causal relations among substorm phenomena.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40931054 and 41174141)National Basic Research Program of China ("973" Program) (Grant No. 2011CB811404)
文摘This paper using the dataset of BBFs (bursty bulk flows) observed by two Cluster satellites C1 and C4 studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time differences of most of BBFs observed by C1 and C4 are smaller than 60 s. The average onset time difference of BBFs of C1 and C4 is 68.5 s. The probabilities of onset time difference of BBFs of C1 and C4 larger than 30 60 90 and 120 s are respectively 55% 35% 27% and 23%. The largest onset time difference of BBFs of C1 and C4 decreases with the increase of earthward component of maximum velocities of BBFs. The onset time difference of BBFs of C1 and C4 results from the velocity inhomogeneity inside the flow channel of BBF which may be produced in propagation path and/or in source region of BBFs. Such a wide range of onset time difference of BBFs suggests that the velocity inhomogeneity inside the flow channel of BBF is various. These results are very important to the current study of substorm research based on THEMIS data because they indicate that it is impossible to determine the onset time of BBF with a single satellite.
