Navigation integration of a mobile robot in dynamic environments

This article presents a design and experimental study of navigation integration of an intelligent mobile robot in dynamic environments. The proposed integration architecture is based on the virtual‐force concept, by which each navigation resource is assumed to exert a virtual force on the robot. The resultant force determines how the robot will move. Reactive behavior and proactive planning can both be handled in a simple and uniform manner using the proposed integration method. A real‐time motion predictor is employed to enable the mobile robot to deal in advance with moving obstacles. A grid map is maintained using on‐line sensory data for global path planning, and a bidirectional algorithm is proposed for planning the shortest path for the robot by using updated grid‐map information. Therefore, the mobile robot has the capacity to both learn and adapt to variations. To implement the whole navigation system efficiently, a blackboard model is used to coordinate the computation on board the vehicle. Simulation and experimental results are presented to verify the proposed design and demonstrate smooth navigation behavior of the intelligent mobile robot in dynamic environments. ©1999 John Wiley & Sons, Inc.     

基于地面视差分布的栅格地图建立方法

针对使用立体视觉建立环境地图方法存在信息不完整的问题,提出一种基于地面视差分布的栅格地图建立方法。利用地面视差分布在视差图中进行障碍物和地面点的检测,通过统一但参数值不同的投影模型将障碍物像素和地面点像素投影到栅格地图中,同时考虑立体视觉的量化和匹配误差、地面视差和栅格占据概率的空间分布。通过在非结构化环境中的实验表明,该方法可以实时地建立信息完整且准确的栅格地图。     

Creating and Preserving Vortical Details in SPH Fluid

We present a new method to create and preserve the turbulent details generated around moving objects in SPH fluid. In our approach, a high‐resolution overlapping grid is bounded to each object and translates with the object. The turbulence formation is modeled by resolving the local flow around objects using a hybrid SPH‐FLIP method. Then these vortical details are carried on SPH particles flowing through the local region and preserved in the global field in a synthetic way. Our method provides a physically plausible way to model the turbulent details around both rigid and deformable objects in SPH fluid, and can efficiently produce animations of complex gaseous phenomena with rich visual details.     

SAR observations of Arctic freeze-up compared to SSM/I during ARCTIC'91

Ice concentration in the Arctic derived from ERS-1 Synthetic Aperture Radar (SAR) and Special Scanning Microwave/Imager (SSM/I) images are compared. The satellite data are compared to video images and in situ measurements. The data were acquired during the freeze-up period of the ARCTIC'91 expedition. The studied areas were characterized by melting conditions and new ice formation with frost flowers. The ERS-1 SAR images are classified by a local averaging method and a segmentation method. Parameters for the methods are derived from the backscattering distributions. Temporal sequences and meteorological information are used for consistent results. Ice concentration derived from SAR are compared with the SSM/I ice concentration (NASA team algorithm) and ship observations. SSM/I may underestimate the ice concentration by 20 per cent due to thin ice formation and melting conditions while SAR may overestimate. However, by using the SAR estimate of the different ice classes we believe it is possible to increase the accuracy of the NASA team algorithm. We conclude that it is important to compare results from different sensors and methods.     

实时更新的全局一致三维栅格建图

在未知的三维环境中,移动机器人自主导航通常需要实时构建与环境全局一致的栅格地图,而现有大部分系统缺少地图更新策略,构建的栅格地图与实际环境不一致.文中将同步定位与建图模块获得的环境信息以点云形式提供给栅格建图模块处理,同时提出基于关键帧的高效数据结构和地图实时更新策略,实时构建可用于移动机器人自主导航的全局一致的地图.室内动态的实验数据测试表明,文中方法可以有效实时更新地图,生成与环境一致的三维栅格地图,支持其后续的自主导航操作.     

基于粒子聚合重采样的移动机器人蒙特卡洛定位

提出了一种基于粒子聚合重采样的移动机器人聚合蒙特卡洛定位（Merge Monte Carlo localization,Merge-MCL）方法．首先将移动机器人作业空间划分为离散栅格,建立栅格集,然后提出一种基于粒子空间相近性的粒子聚合技术, 在保证粒子空间分布合理性的同时自适应调整粒子集规模．提出的粒子聚合重采样方法能够缓解粒子权值退化问题, 并避免了传统重采样方法导致的多样性匮乏问题．仿真结果表明,粒子聚合重采样方法能够有效控制粒子集规模, 聚合蒙特卡洛定位方法是鲁棒、有效的．     

基于环约束的虚拟人动态LOD技术

针对虚拟人体模型及其运动序列提出一种简化方法．首先在人体骨架节点（关节）等基本模型表面附近添加环形约束，结合Qslim算法生成基本简化模型；其次利用顶点混合方法从基本简化模型生成简化序列．实验结果表明。该方法可生成逼真的简化运动序列，且在简化过程和LOD控制过程中均独立于具体运动序列，适合规模群体的实时驱动．     

基于网格状模板的实时图像跟踪算法

传统相关跟踪算法存在运算量大和实时性差的缺陷.针对这一问题,提出了一种基于网格状模板的实时图像跟踪算法.该算法首先从减少参与匹配运算的像素数目的角度出发,剔除部分冗余像素,将匹配模板设置为网格状.然后在成像跟踪仿真实验平台下,用归一化互相关匹配方法实现了对运动目标的跟踪.仿真实验结果表明,该算法不仅在很大程度上减少了图像匹配的计算量,提高了跟踪实时性,而且跟踪快速准确,具有一定的实用价值.     

基于概率栅格地图的移动机器人可定位性估计

基于广泛使用的概率栅格地图,提出了一种移动机器人可定位性估计方法.通过对定位Fisher信息矩阵进行栅格离散化,提出了静态可定位性矩阵,该矩阵适用于已知地图条件下的离线估计.在此基础上,针对在线估计中环境存在的非预期动态变化问题,采用局部感知的未知障碍物影响因子来修正静态可定位性矩阵,进而得到动态可定位性矩阵,该矩阵定量描述了机器人可定位性能力及其方向性.各种典型环境下的机器人实验结果表明了所提方法的有效性.     

海冰与海洋平台碰撞分析中的可视化方法

针对基于离散元方法的海冰与海洋平台结构碰撞分析系统,对运行于CPU GPU异构高性能计算平台上的大规模粒子模拟进行可视化方法的研究.使用OpenGL完成不同规模的平整冰、浮冰、冰脊和不规则形态海冰的呈现,不同形状海洋平台结构与受力网格的绘制,海冰粒子的运动轨迹与速度的表达,海浪效果的模拟以及碰撞过程的动画演示等.通过定义合理的交互模式与接口,在一定程度上融合GPU加速的离散元计算与后处理显示,基于多进程管道通信、多线程并行输出等实现在GPU加速计算的同时实时显示粒子模拟计算结果.该方法在帮助研究者随时掌握程序执行状况的同时,大幅减少后续传输、处理和存储的数据.     

Control of leader–follower formation and path planning of mobile robots using Asexual Reproduction Optimization (ARO)

This paper presents the optimal path of nonholonomic multi robots with coherent formation in a leader–follower structure in the presence of obstacles using Asexual Reproduction Optimization (ARO). The robots path planning based on potential field method are accomplished and a novel formation controller for mobile robots based on potential field method is proposed. The efficiency of the proposed method is verified through simulation and experimental studies by applying them to control the formation of four e-Pucks robots (low-cost mobile robot platform). Also the proposed method is compared with Simulated Annealing, Improved Harmony Search and Cuckoo Optimization Algorithm methods and the experimental results, higher performance and fast convergence time to the best solution of the ARO demonstrated that this optimization method is appropriate for real time control application.     

栅格地图环境下机器人速度势实时路径规划

针对智能制造工程环境中移动机器人的自动避障问题,提出一种基于栅格地图的移动机器人速度势实时避障路径规划方法。利用栅格法二值化移动机器人的工作场景,从机器人中心出发向不同方向进行栅格搜索。基于障碍物对移动机器人有排斥作用以及目标点对机器人有吸引作用的思想,通过栅格数的累加计算机器人到障碍物之间的实时距离,并以此为参数,考虑障碍物的形状、最小安全距离等因素的影响来建立负的速度增量函数;以机器人当前位置与目标点的实时距离和角度为参数建立正向速度增量函数。进而在机器人运动学模型基础上,定义速度势函数来对移动机器人进行实时速度驱动。通过设置最小速度增量,避免在零势点处的局部极小点问题;通过设立距离阈值,避免在目标点附近速度增量趋于无穷的问题。通过仿真对所提出的算法进行验证。     

Probabilistic terrain classification in unstructured environments

Autonomous navigation in unstructured environments is a complex task and an active area of research in mobile robotics. Unlike urban areas with lanes, road signs, and maps, the environment around our robot is unknown and unstructured. Such an environment requires careful examination as it is random, continuous, and the number of perceptions and possible actions are infinite.We describe a terrain classification approach for our autonomous robot based on Markov Random Fields (MRFs ) on fused 3D laser and camera image data. Our primary data structure is a 2D grid whose cells carry information extracted from sensor readings. All cells within the grid are classified and their surface is analyzed in regard to negotiability for wheeled robots.Knowledge of our robot’s egomotion allows fusion of previous classification results with current sensor data in order to fill data gaps and regions outside the visibility of the sensors. We estimate egomotion by integrating information of an IMU, GPS measurements, and wheel odometry in an extended Kalman filter.In our experiments we achieve a recall ratio of about 90% for detecting streets and obstacles. We show that our approach is fast enough to be used on autonomous mobile robots in real time.     

室外自主移动机器人AMOR的导航技术

在非结构化环境,移动机器人行驶运动规划和自主导航是非常挑战性的问题。基于实时的动态栅格地图,提出了一个快速的而又实效的轨迹规划算法,实现机器人在室外环境的无碰撞运动导航。AMOR是自主研发的室外运动移动机器人,它在2007年欧洲C-ELROB大赛中赢得了野外自主侦察比赛的冠军。它装备了SICK的激光雷达,用来获取机器人运动前方的障碍物体信息,建立实时动态的环境地图。以A*框架为基础的改造算法,能够在众多的路径中快速地找到最佳的安全行驶路径,实现可靠的自主导航。所有的测试和比赛结果表明所提方案是可行的、有效的。     

Sonar Map Construction for Autonomous Mobile Robots Using a Data Association Filter

This paper presents a method for building a probability grid map for autonomous mobile robots with ultrasonic sensors using a data association filter (DAF). The method is based on evaluating the possibility that the acquired sonar data are all reflected by the same object. The DAF is able to associate data points with each other. Data affected by specular reflection are not likely to be associated with the same object, so they are excluded from the data cluster by the DAF, thereby improving the reliability of the data used for the probability grid map. Since the corrupted data are not used to update the probability map, it is possible to build a good quality grid map even in a specular environment. The DAF was applied to the Bayesian and the Orientation probability models, which are typical models used to build grid maps, to verify its effectiveness. Experimental results were also obtained using a mobile robot in a real-world environment.     

Grid-partition index: a hybrid method for nearest-neighbor queries in wireless location-based services

Traditional nearest-neighbor (NN) search is based on two basic indexing approaches: object-based indexing and solution-based indexing. The former is constructed based on the locations of data objects: using some distance heuristics on object locations. The latter is built on a precomputed solution space. Thus, NN queries can be reduced to and processed as simple point queries in this solution space. Both approaches exhibit some disadvantages, especially when employed for wireless data broadcast in mobile computing environments. In this paper, we introduce a new index method, called the grid-partition index, to support NN search in both on-demand access and periodic broadcast modes of mobile computing. The grid-partition index is constructed based on the Voronoi diagram, i.e., the solution space of NN queries. However, it has two distinctive characteristics. First, it divides the solution space into grid cells such that a query point can be efficiently mapped into a grid cell around which the nearest object is located. This significantly reduces the search space. Second, the grid-partition index stores the objects that are potential NNs of any query falling within the cell. The storage of objects, instead of the Voronoi cells, makes the grid-partition index a hybrid of the solution-based and object-based approaches. As a result, it achieves a much more compact representation than the pure solution-based approach and avoids backtracked traversals required in the typical object-based approach, thus realizing the advantages of both approaches. We develop an incremental construction algorithm to address the issue of object update. In addition, we present a cost model to approximate the search cost of different grid partitioning schemes. The performances of the grid-partition index and existing indexes are evaluated using both synthetic and real data. The results show that, overall, the grid-partition index significantly outperforms object-based indexes and solution-based indexes. Furthermore, we extend the grid-partition index to support continuous-nearest-neighbor search. Both algorithms and experimental results are presented. Edited by R. Guting     

动态3维场景中多角色动画的交互式模拟研究

当前角色动画的合成大多是在预设的场景中,采用导入与角色骨骼模型匹配的运动捕获数据的方法,这就满足不了多种拓扑结构的骨骼模型和实时变化场景的需要。针对上述问题,提出重定向运动捕获数据到多个任意骨骼拓扑结构的算法,通过采用以实时3维动态寻径算法为基础的角色智能寻径模型,结合语音用户接口代替图形用户接口的方法,实现虚拟角色在动态3维场景中的真实感运动。实验结果表明,本方法可以合成流畅而逼真的,与环境实时交互的角色动画,提高了数据重用性,降低了动画合成成本,满足不同动态3维场景中动画合成的需要。     

Classifying watermelon ripeness by analysing acoustic signals using mobile devices

This work addresses the problem of distinguishing between ripe and unripe watermelons using mobile devices. Through analysing ripeness-related features extracted by thumping watermelons, collecting acoustic signals by microphones on mobile devices, our method can automatically identify the ripeness of watermelons. This is possible in real time, making use of machine learning techniques to provide good accuracy. We firstly collect a training dataset comprising acoustic signals generated by thumping both ripe and unripe watermelons. Audio signal analysis on this helps identify features related to watermelon ripeness. These features are then used to construct a classification model for future signals. Based on this, we developed a crowdsourcing application for Android which allows users to identify watermelon ripeness in real time while submitting their results to us allowing continuous improvement of the classification model. Experimental results show that our method is currently able to correctly classify ripe and unripe watermelons with an overall accuracy exceeding 89 %.     

输电线路智能融冰辅助决策关键技术研究与实现

冰雪天气是对电力系统稳定运行影响最大的自然灾害之一,会造成输电线路覆冰,危害电网安全运行。本文围绕线路融冰方案编制的流程展开,针对流程中的重点和难点步骤,研究辅助决策的智能技术,以提高电网调控中心融冰方案编制质量和实效性。具体内容如下：针对实际电网运行数据和覆冰数据进行预处理,实现了多源数据融合,基于深度优先算法进行可停电融冰线路分析;采用加权均值综合评判的方法,基于多指标对融冰线路进行优先级排序和组合;基于直流潮流支路开断分布因子的评估方法,对融冰方案进行快速校核;基于多机多任务并行处理技术,对融冰方案进行详细校核,以此来提高输电线路融冰方案安排效率,保证电网在冰雪天气的安全稳定运行。     

Context preserving maps of tubular structures

When visualizing tubular 3D structures, external representations are often used for guidance and display, and such views in 2D can often contain occlusions. Virtual dissection methods have been proposed where the entire 3D structure can be mapped to the 2D plane, though these will lose context by straightening curved sections. We present a new method of creating maps of 3D tubular structures that yield a succinct view while preserving the overall geometric structure. Given a dominant view plane for the structure, its curve skeleton is first projected to a 2D skeleton. This 2D skeleton is adjusted to account for distortions in length, modified to remove intersections, and optimized to preserve the shape of the original 3D skeleton. Based on this shaped 2D skeleton, a boundary for the map of the object is obtained based on a slicing path through the structure and the radius around the skeleton. The sliced structure is conformally mapped to a rectangle and then deformed via harmonic mapping to match the boundary placement. This flattened map preserves the general geometric context of a 3D object in a 2D display, and rendering of this flattened map can be accomplished using volumetric ray casting. We have evaluated our method on real datasets of human colon models.