The existing nearest neighbor query methods cannot directly perform the nearest neighbor query of specified geographical direction space.In order to compensate the shortcomings of the existing methods,a directional ne...The existing nearest neighbor query methods cannot directly perform the nearest neighbor query of specified geographical direction space.In order to compensate the shortcomings of the existing methods,a directional nearest neighbor query method in specific direction space based on Voronoi diagram is put forward.This work studies two cases,i.e.the query point is static and the query point moves with a constant velocity.Under the static condition,the corresponding pruning method and the pruning algorithm of the specified direction nearest neighbor(pruning_SDNN algorithm)are proposed by combining the plane right-angle coordinate system with the north-west direction,and then according to the smallest external rectangle of Voronoi polygon,the specific query is made and the direction nearest neighbor query based on Voronoi rectangle(VR-DNN) algorithm is given.In the case of moving with a constant velocity,first of all,the combination of plane right angle coordinate system,geographical direction and circle are used,the query range is determined and pruning methods and the pruning algorithm of the direction nearest neighbor based on decision circle(pruning_DDNN algorithm) are put forward.Then,according to the different position of motion trajectory and Voronoi diagram,a specific query through the nature of Voronoi diagram is given.At last,the direction nearest neighbor query based on Voronoi diagram and motion trajectory(VM-DNN) algorithm is put forward.The theoretical research and experiments show that the proposed algorithm can effectively deal with the problem of the nearest neighbor query for a specified geographical direction space.展开更多
Reverse k nearest neighbor （RNNk） is a generalization of the reverse nearest neighbor problem and receives increasing attention recently in the spatial data index and query. RNNk query is to retrieve all the data po...Reverse k nearest neighbor （RNNk） is a generalization of the reverse nearest neighbor problem and receives increasing attention recently in the spatial data index and query. RNNk query is to retrieve all the data points which use a query point as one of their k nearest neighbors. To answer the RNNk of queries efficiently, the properties of the Voronoi cell and the space-dividing regions are applied. The RNNk of the given point can be found without computing its nearest neighbors every time by using the rank Voronoi cell. With the elementary RNNk query result, the candidate data points of reverse nearest neighbors can he further limited by the approximation with sweepline and the partial extension of query region Q. The approximate minimum average distance （AMAD） can be calculated by the approximate RNNk without the restriction of k. Experimental results indicate the efficiency and the effectiveness of the algorithm and the approximate method in three varied data distribution spaces. The approximate query and the calculation method with the high precision and the accurate recall are obtained by filtrating data and pruning the search space.展开更多
Aggregate nearest neighbor(ANN) search retrieves for two spatial datasets T and Q, segment(s) of one or more trajectories from the set T having minimum aggregate distance to points in Q. When interacting with large am...Aggregate nearest neighbor(ANN) search retrieves for two spatial datasets T and Q, segment(s) of one or more trajectories from the set T having minimum aggregate distance to points in Q. When interacting with large amounts of trajectories, this process would be very time-consuming due to consecutive page loads. An approximate method for finding segments with minimum aggregate distance is proposed which can improve the response time. In order to index large volumes of trajectories, scalable and efficient trajectory index(SETI) structure is used. But some refinements are provided to temporal index of SETI to improve the performance of proposed method. The experiments were performed with different number of query points and percentages of dataset. It is shown that proposed method besides having an acceptable precision, can reduce the computation time significantly. It is also shown that the main fraction of search time among load time, ANN and computing convex and centroid, is related to ANN.展开更多
针对水声目标信号复杂、样本获取难度大且富含不确定信息的问题,研究了一种新的证据K类近邻识别算法(Evidence K Nearest Neighbor,EK-NN)。首先在水声目标的各类训练样本中,根据特征距离大小选取待识别目标的K近邻,并构造其基本置信指...针对水声目标信号复杂、样本获取难度大且富含不确定信息的问题,研究了一种新的证据K类近邻识别算法(Evidence K Nearest Neighbor,EK-NN)。首先在水声目标的各类训练样本中,根据特征距离大小选取待识别目标的K近邻,并构造其基本置信指派函数。然后使用证据理论中的Dempster-Shafer(D-S)规则对各类别下的近邻证据进行组合,最后再应用冲突置信的比例分配规则5(Redistribute Conflicting mass proportionally rule5,PCR5)将所有类别的组合证据进行融合,并根据融合结果和所设立的分类规则来判断目标的类别属性。根据水声目标实测数据,将新算法与其他几种常见的水声目标识别算法进行了对比分析,结果表明新算法能有效提高识别的准确率。展开更多
在车联网场景中,现有基于位置服务的隐私保护方案存在不支持多种类型K近邻兴趣点的并行查询、难以同时保护车辆用户和位置服务提供商(Location-Based Service Provider,LBSP)两方隐私、无法抵抗恶意攻击等问题。为了解决上述问题,提出...在车联网场景中,现有基于位置服务的隐私保护方案存在不支持多种类型K近邻兴趣点的并行查询、难以同时保护车辆用户和位置服务提供商(Location-Based Service Provider,LBSP)两方隐私、无法抵抗恶意攻击等问题。为了解决上述问题,提出了一种保护两方隐私的多类型的路网K近邻查询方案MTKNN-MPP。将改进的k-out-of-n不经意传输协议应用于K近邻查询方案中,实现了在保护车辆用户的查询内容隐私和LBSP的兴趣点信息隐私的同时,一次查询多种类型K近邻兴趣点。通过增设车载单元缓存机制,降低了计算代价和通信开销。安全性分析表明,MTKNN-MPP方案能够有效地保护车辆用户的位置隐私、查询内容隐私以及LBSP的兴趣点信息隐私,可以保证车辆的匿名性,能够抵抗合谋攻击、重放攻击、推断攻击、中间人攻击等恶意攻击。性能评估表明,与现有典型的K近邻查询方案相比,MTKNN-MPP方案具有更高的安全性,且在单一类型K近邻查询和多种类型K近邻查询中,查询延迟分别降低了43.23%~93.70%,81.07%~93.93%。展开更多
基金Supported by the National Natural Science Foundation of China(No.61872105,62072136)the Natural Science Foundation of Heilongjiang Province(No.LH2020F047)+1 种基金the Scientific Research Foundation for Returned Scholars Abroad of Heilongjiang Province of China(No.LC2018030)the National Key R&D Program of China(No.2020YFB1710200)。
文摘The existing nearest neighbor query methods cannot directly perform the nearest neighbor query of specified geographical direction space.In order to compensate the shortcomings of the existing methods,a directional nearest neighbor query method in specific direction space based on Voronoi diagram is put forward.This work studies two cases,i.e.the query point is static and the query point moves with a constant velocity.Under the static condition,the corresponding pruning method and the pruning algorithm of the specified direction nearest neighbor(pruning_SDNN algorithm)are proposed by combining the plane right-angle coordinate system with the north-west direction,and then according to the smallest external rectangle of Voronoi polygon,the specific query is made and the direction nearest neighbor query based on Voronoi rectangle(VR-DNN) algorithm is given.In the case of moving with a constant velocity,first of all,the combination of plane right angle coordinate system,geographical direction and circle are used,the query range is determined and pruning methods and the pruning algorithm of the direction nearest neighbor based on decision circle(pruning_DDNN algorithm) are put forward.Then,according to the different position of motion trajectory and Voronoi diagram,a specific query through the nature of Voronoi diagram is given.At last,the direction nearest neighbor query based on Voronoi diagram and motion trajectory(VM-DNN) algorithm is put forward.The theoretical research and experiments show that the proposed algorithm can effectively deal with the problem of the nearest neighbor query for a specified geographical direction space.
基金Supported by the National Natural Science Foundation of China (60673136)the Natural Science Foundation of Heilongjiang Province of China (F200601)~~
文摘Reverse k nearest neighbor （RNNk） is a generalization of the reverse nearest neighbor problem and receives increasing attention recently in the spatial data index and query. RNNk query is to retrieve all the data points which use a query point as one of their k nearest neighbors. To answer the RNNk of queries efficiently, the properties of the Voronoi cell and the space-dividing regions are applied. The RNNk of the given point can be found without computing its nearest neighbors every time by using the rank Voronoi cell. With the elementary RNNk query result, the candidate data points of reverse nearest neighbors can he further limited by the approximation with sweepline and the partial extension of query region Q. The approximate minimum average distance （AMAD） can be calculated by the approximate RNNk without the restriction of k. Experimental results indicate the efficiency and the effectiveness of the algorithm and the approximate method in three varied data distribution spaces. The approximate query and the calculation method with the high precision and the accurate recall are obtained by filtrating data and pruning the search space.
文摘Aggregate nearest neighbor(ANN) search retrieves for two spatial datasets T and Q, segment(s) of one or more trajectories from the set T having minimum aggregate distance to points in Q. When interacting with large amounts of trajectories, this process would be very time-consuming due to consecutive page loads. An approximate method for finding segments with minimum aggregate distance is proposed which can improve the response time. In order to index large volumes of trajectories, scalable and efficient trajectory index(SETI) structure is used. But some refinements are provided to temporal index of SETI to improve the performance of proposed method. The experiments were performed with different number of query points and percentages of dataset. It is shown that proposed method besides having an acceptable precision, can reduce the computation time significantly. It is also shown that the main fraction of search time among load time, ANN and computing convex and centroid, is related to ANN.
文摘为了改善利用SCATS交通数据估计路段行程时间的效果,通过分析SCATS实际交通数据获取时间间隔不一致的特征,构建了SCATS交通数据虚拟时间序列,将利用因子分析法提取的累计贡献率在85%以上的主因子作为交通模式特征向量的构成要素,用欧氏距离作为当前交通模式特征向量和历史交通模式特征向量相似性的测度指标,以路段行程时间估计误差最小为目标选取当前交通模式的近邻数,对交通模式之间距离的倒数进行归一化处理,确定了相似交通模式的行程时间权重,设计了基于SCATS交通数据的路段行程时间估计方法.实例结果表明:与多元线性回归方法相比,本文方法估计的路段行程时间平均绝对误差、平均绝对百分比误差和均方根误差分别平均减少了9.68 s、8.07%和4.5 s.
文摘针对水声目标信号复杂、样本获取难度大且富含不确定信息的问题,研究了一种新的证据K类近邻识别算法(Evidence K Nearest Neighbor,EK-NN)。首先在水声目标的各类训练样本中,根据特征距离大小选取待识别目标的K近邻,并构造其基本置信指派函数。然后使用证据理论中的Dempster-Shafer(D-S)规则对各类别下的近邻证据进行组合,最后再应用冲突置信的比例分配规则5(Redistribute Conflicting mass proportionally rule5,PCR5)将所有类别的组合证据进行融合,并根据融合结果和所设立的分类规则来判断目标的类别属性。根据水声目标实测数据,将新算法与其他几种常见的水声目标识别算法进行了对比分析,结果表明新算法能有效提高识别的准确率。
文摘在车联网场景中,现有基于位置服务的隐私保护方案存在不支持多种类型K近邻兴趣点的并行查询、难以同时保护车辆用户和位置服务提供商(Location-Based Service Provider,LBSP)两方隐私、无法抵抗恶意攻击等问题。为了解决上述问题,提出了一种保护两方隐私的多类型的路网K近邻查询方案MTKNN-MPP。将改进的k-out-of-n不经意传输协议应用于K近邻查询方案中,实现了在保护车辆用户的查询内容隐私和LBSP的兴趣点信息隐私的同时,一次查询多种类型K近邻兴趣点。通过增设车载单元缓存机制,降低了计算代价和通信开销。安全性分析表明,MTKNN-MPP方案能够有效地保护车辆用户的位置隐私、查询内容隐私以及LBSP的兴趣点信息隐私,可以保证车辆的匿名性,能够抵抗合谋攻击、重放攻击、推断攻击、中间人攻击等恶意攻击。性能评估表明,与现有典型的K近邻查询方案相比,MTKNN-MPP方案具有更高的安全性,且在单一类型K近邻查询和多种类型K近邻查询中,查询延迟分别降低了43.23%~93.70%,81.07%~93.93%。
