树高是监测森林状况的重要参数,摄影测量法具有低成本、灵活的特性,是树高采集的重要方法之一.作为一种被动遥感方式,传统的摄影测量方法往往需要数量较多,重叠率较高的图像数据,这与传统图像特征的稀疏性有关.为了提高图像数量受限条...树高是监测森林状况的重要参数,摄影测量法具有低成本、灵活的特性,是树高采集的重要方法之一.作为一种被动遥感方式,传统的摄影测量方法往往需要数量较多,重叠率较高的图像数据,这与传统图像特征的稀疏性有关.为了提高图像数量受限条件下的树高提取精度,提出将稀疏特征匹配和稠密像素匹配相结合,并使用对极约束过滤外点的方法,得到稠密且精度较高的匹配结果,并通过三维重建算法得到森林场景点云.该方法在少量图像的情况下就可以较为完整地重建森林场景并提取树高,将提取的树高与机载激光雷达(light detection and ranging,LiDAR)点云的结果进行对比,相关系数为0.91,最大误差为1.64 m.该算法只需要少量的重叠图像,这表明了该算法在处理高分辨率卫星图像方面具有一定潜力.展开更多
The existing research on dynamics and slip ratio of wheeled mobile robot （WMR） are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the...The existing research on dynamics and slip ratio of wheeled mobile robot （WMR） are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS- Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS- Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified, Moreover, the relative horizontal motion between fore/hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore/hind wheels become larger/smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.展开更多
将气压测高方法应用于基于通信卫星的中国区域定位系统(Chinese Area Positioning System,CAPS)中,可以补充卫星星座、改善星座布局、提高定位精度。介绍了气压测高原理、高程约束定位解算模型和方法,在CAPS-I期系统中进行了仿真计算与...将气压测高方法应用于基于通信卫星的中国区域定位系统(Chinese Area Positioning System,CAPS)中,可以补充卫星星座、改善星座布局、提高定位精度。介绍了气压测高原理、高程约束定位解算模型和方法,在CAPS-I期系统中进行了仿真计算与分析,对高程约束下CAPS的定位精度情况以及气压测高自身误差对定位精度的影响进行了深入的研究和探讨,从而为气压测高下的实际定位工作提供了指导与参考。展开更多
文摘树高是监测森林状况的重要参数,摄影测量法具有低成本、灵活的特性,是树高采集的重要方法之一.作为一种被动遥感方式,传统的摄影测量方法往往需要数量较多,重叠率较高的图像数据,这与传统图像特征的稀疏性有关.为了提高图像数量受限条件下的树高提取精度,提出将稀疏特征匹配和稠密像素匹配相结合,并使用对极约束过滤外点的方法,得到稠密且精度较高的匹配结果,并通过三维重建算法得到森林场景点云.该方法在少量图像的情况下就可以较为完整地重建森林场景并提取树高,将提取的树高与机载激光雷达(light detection and ranging,LiDAR)点云的结果进行对比,相关系数为0.91,最大误差为1.64 m.该算法只需要少量的重叠图像,这表明了该算法在处理高分辨率卫星图像方面具有一定潜力.
基金supported by National Outstanding Youth Science Foundation of China (Grant No. 51125020)National Hi-tech Research and Development Program of China (863 Program, Grant No. 2006AA04Z207)Program for New Century Excellent Talents in University, China
文摘The existing research on dynamics and slip ratio of wheeled mobile robot （WMR） are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS- Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS- Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified, Moreover, the relative horizontal motion between fore/hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore/hind wheels become larger/smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.
文摘将气压测高方法应用于基于通信卫星的中国区域定位系统(Chinese Area Positioning System,CAPS)中,可以补充卫星星座、改善星座布局、提高定位精度。介绍了气压测高原理、高程约束定位解算模型和方法,在CAPS-I期系统中进行了仿真计算与分析,对高程约束下CAPS的定位精度情况以及气压测高自身误差对定位精度的影响进行了深入的研究和探讨,从而为气压测高下的实际定位工作提供了指导与参考。
