2-D delineation of individual citrus trees from UAV-based dense photogrammetric surface models   总被引：1，自引：0，他引：1  

Ali Ozgun Ok  Asli Ozdarici-Ok 《International Journal of Digital Earth》2018,11(6):583-608

One of the challenges of remote sensing and computer vision lies in the three-dimensional (3-D) reconstruction of individual trees by using automated methods through very high-resolution (VHR) data sets. However, a successful and complete 3-D reconstruction relies on precise delineation of the trees in two dimensions. In this paper, we present an original approach to detect and delineate citrus trees using unmanned aerial vehicles based on photogrammetric digital surface models (DSMs). The symmetry of the citrus trees in a DSM is handled by an orientation-based radial symmetry transform which is computed in a unique way. Next, we propose an efficient strategy to accurately build influence regions of each tree, and then we delineate individual citrus trees through active contours by taking into account the influence region of each canopy. We also present two efficient strategies to filter out erroneously detected canopy regions without having any height thresholds. Experiments are carried out on eight test DSMs composed of different types of citrus orchards with varying densities and canopy sizes. Extensive comparisons to the state-of-the-art approaches reveal that our proposed approach provides superior detection and delineation performances through supporting a nice balance between precision and recall measures.  相似文献   

A joint distribution of significant wave height and characteristic surf parameter     

Dag Myrhaug  Sébastien Fouques 《Coastal Engineering》2010

The paper provides a joint distribution of significant wave height and characteristic surf parameter. The characteristic surf parameter is given by the ratio between the slope of a beach or a structure and the square root of the characteristic wave steepness in deep water defined in terms of the significant wave height and the spectral peak period. The characteristic surf parameter is used to characterize surf zone processes and is relevant for e.g. wave run-up on beaches and coastal structures. The paper presents statistical properties of the wave parameters as well as an example of results corresponding to typical field conditions.  相似文献   

The interaction of two asymmetric quasi-geostrophic vortex patches     

M. M. Jalali 《地球物理与天体物理流体动力学》2013,107(6):375-401

ABSTRACT

Herein we study the general interaction of two vortex patches in a single-layer quasi-geostrophic shallow-water flow. Steadily-rotating equilibrium states are found over a wide parameter space spanning the Rossby deformation length, vortex area ratio, potential vorticity ratio, and gap between their innermost edges. A linear stability analysis is then used to identify the critical gap separating stable and unstable solutions, over the entire range of area and potential vorticity ratios, and for selected values of the Rossby deformation length. A representative set of marginally unstable equilibrium states are then slightly perturbed and evolved by an accurate contour dynamics numerical algorithm to understand the long-term fate of the instabilities. Not all instabilities lead to vortex merger; many in fact are characterised by weak filamentation and a small adjustment of the vortex shapes, without merger. Stronger instabilities lead to material being torn from one vortex and either wrapped around the other or reduced to ever thinning filamentary debris. A portion of the vortex may survive, or it may be completely strained out by the other.  相似文献   

地形图等高线成组综合的试验   总被引：15，自引：0，他引：15  

费立凡 《武汉大学学报(信息科学版)》1993,(Z1)

本文在讨论制图自动综合一般问题的基础上,着重分析了两种等高线自动综合的技术路线存在的优缺点。笔者提出,采用模拟人类专家智能的方法,从二维的等高线输入数据出发,提取地貌结构信息,从而对等高线进行成组的综合,直接形成经综合的二维等高线输出数据,有可能获得较为简捷,效果良好的综合结果。在对这条技术路线进行实验的过程中所涉及的人工智能问题,主要包括:对无序数字化等高线数据的整理、等高线上重要特征点的识别、正负向地貌特征的确定、谷地点的选出、谷底线的自动跟踪、谷地重要性的计算、谷间距的自动量算、对称谷地的寻找、综合后图形的生成等。  相似文献   

CONTOUR DYNAMICS FOR VORTEX MOTION INFLUENCED BY THE CORIOLIS FORCE^*          下载免费PDF全文

Luo Zhexian 《Acta Meteorologica Sinica》1994,8(1):60-71

The computational formulae are given for single-contour constant-value vortex motion influenced by the Coriolis force in the framework of contour dynamics,by which four numerical computations are performed,the result exhibiting their validity.  相似文献   

用物质线的轨迹积分方法研究阻塞     

张绍晴  陈久康 《南京气象学院学报》1992,15(3):315-322

  相似文献   

复杂等高线自动综合的分形处理方法研究     

王桥  吴纪桃 《测绘学院学报》1995,(2)

复杂等高线自动综合是计算机辅助制图领域中一项重要且难度较大的任务。本文根据分形理论的基本原理，提出了一种基于量化等高线形状结构特征的复杂等高线自动综合的新方法。研究和实验表明，该方法充分顾及了地貌形态特征，能够对等高线图形进行客观、有效地概括。  相似文献   

四边形法绘制水下河床等深线图     

闻道秋 《测绘工程》1999,8(3):21-25

根据水下河床水深点测量采样的既有规则格网法又有三角形法二者优点的四边形法绘制河床等深线图,该法数据结构简单,编程方便,速度快。文 图表对水下对河床水深点的数据数据结构,四边形的构万能主等深线的追踪作了详细的讨论。  相似文献   

基于IGRF的地磁基准图技术   总被引：1，自引：0，他引：1  

陈贵芳  郁丰  王润 《地震地磁观测与研究》2020,41(3):98-104

地磁导航需要获得目标区域的地磁基准图。研究了基于国际地磁参考场的地磁场要素计算和等值线绘制方法。以给定目标区域的经纬高为输入,计算高阶地磁球谐函数获取地磁矢量并计算地磁场要素,修正了因地球扁率带来的数据差异。采用具有虚节点的移动矩形网格算法来绘制地磁参数等值线,生成目标区域的地磁基准图。采用C#实现了地磁基准图软件,测试表明,获得的地磁等高线数据满足使用要求,等值线精度较高。  相似文献   

基于区间树索引的等高线提取算法   总被引：1，自引：0，他引：1  

王涛  毋河海  刘纪平 《武汉大学学报(信息科学版)》2007,32(2):131-134

重新设计了从高程格网中提取等高线过程中的遍历策略，以保证提取结果具有统一的方向；针对日益增长的高程格网数据量，提出了基于区间树索引来查找等高线起点的算法。  相似文献