一种采用基础矩阵描述的核线影像生成方法

设计了一种采用基础矩阵的立体像对核线影像制作方法,由基础矩阵来描述影像间的相对方位关系,避免了相对定向过程中复杂的迭代过程。通过稀疏匹配获取高精度的同名点,由基础矩阵确定每组同名点对应的同名核线,根据核线必相交于核点的原理,采用最小二乘法确定左右影像的核点坐标;然后根据核点坐标完成影像间核线的快速映射,沿核线方向采用双线性内插法进行核线重采样,完成核线影像制作。采用多组影像进行核线影像制作实验,对生成的核线影像进行同名特征点提取与匹配,结果表明采用该方法制作的核线影像上下视差较小,验证了方法的有效性。     

基于普通数码立体影像的同名核线搜索方法

普通相机拍摄的像片越来越成为近景摄影测量的主要数据来源,针对普通相机内方位元素不固定、图像畸变较大的问题,论文提出了先对立体影像进行内方位元素(x0、y0)和畸变系数k1改正、再建立核线影像的操作流程,推导了相关的数学模型,根据实例验证,得到了很好的效果。     

球面全景影像相对定向与精度验证

对传统的5点法相对定向算法的共面误差计算方法进行改进,提出了一种适合球面全景成像特点的相对定向计算流程。与传统方法相同,该算法首先计算本质矩阵,然后对本质矩阵进行奇异值分解得到旋转矩阵和平移矢量的候选解,最后利用重建的物方三维点坐标排除错误解。本文的贡献在于推导了球面全景共面条件公式,并使用点到核线平面的球面距离作为球面全景共面条件的误差项。模拟数据试验显示:当图像特征点的随机噪声在[-0.5,0.5]像素范围内时,3个姿态角的中误差约为0.1°,由相对定向恢复的相对平移量与模拟值的夹角中误差约为1.5°。使用车载全景相机配合POS获取的数据进行试验的结果显示:横滚角和俯仰角的中误差可以达到0.2°以内,航向角的中误差可以达到0.4°以内,由相对定向恢复的相对平移量与POS平移量的夹角中误差可以达到2°以内。采用本文相对定向算法的结果生成球面全景核线影像,提取影像之间同名点坐标并计算其列方向误差,结果显示核线影像同名点列坐标差的中误差在1个像素以内。     

支持近似最短距离查询的高效图加密机制

近似最短距离查询是图检索的基本模式.为了保护外包数据安全,通常对图数据进行加密.已有加密方案使用两跳覆盖模型构建加密图索引,导致索引结构复杂,降低了查询效率.本文提出了一种基于图压缩的加密机制,可以提高图的检索效率,并且支持加密图最短路径查询.该机制使用K-mediods聚类使得图中的节点按照距离分成K个簇,每个簇内的节点使用其中心节点代理,当查询2个点间最短距离时,对于相同簇内的点直接查询,对于簇间的点使用代理节点查询距离.实验结果表明该机制有效地减少了查询时间,提高了查询效率,且查询结果误差度在可接受范围内.     

Propagation and run-up of nearshore tsunamis with HLLC approximate Riemann solver

A numerical model describing the propagation and run-up process of nearshore tsunamis in the vicinity of shorelines is developed based on an approximate Riemann solver. The governing equations of the model are the nonlinear shallow-water equations. The governing equations are discretized explicitly by using a finite volume method. The nonlinear terms in the momentum equations are solved with the Harten-Lax-van Leer-Contact (HLLC) approximate Riemann solver. The developed model is first applied to prediction of water motions in a parabolic basin, and propagation and subsequent run-up process of nearshore tsunamis around a circular island. Computed results are then compared with available analytical solutions and laboratory measurements. Very reasonable agreements are observed.     

Rapid simulation of multiple radially growing hydraulic fractures using an energy‐based approach

The goal of hydraulic fracturing stimulation of horizontal wells is typically to generate uniform, simultaneously growing hydraulic fractures from 3 to 6 initiation/entry sites that are spaced within a certain interval of the wellbore comprising a so‐called stage. Because of the stress interaction among growing hydraulic fractures, however, it is hard to attain simultaneous growth of all hydraulic fractures. While models have been proven useful for devising mitigation strategies of these so‐called stress‐shadow effects, the required simulations are so computationally expensive that optimization is possible only in the simplest cases. Here, we present an approximate (energy‐based) model capable of running an entire simulation in 1–2s, which is about one million times faster than the benchmark model. The approach is built on asymptotic solutions to approximate growth of radial hydraulic fractures, a far field approximation for the stress shadow interactions among growing hydraulic fractures, and coupling the effect of the stress shadow to fracture growth via a global energy balance equation. We show very close agreement in predictions of the lengths of each fracture in the array between the approximate model and the benchmark model, thus verifying that the new approximate model is useful for optimization of hydraulic fracture design. Copyright © 2015 John Wiley & Sons, Ltd.     

A general framework for error analysis in measurement-based GIS Part 2: The algebra-based probability model for point-in-polygon analysis

This is the second paper of a four-part series of papers on the development of a general framework for error analysis in measurement-based geographic information systems (MBGIS). In this paper, we discuss the problem of point-in-polygon analysis under randomness, i.e., with random measurement error (ME). It is well known that overlay is one of the most important operations in GIS, and point-in-polygon analysis is a basic class of overlay and query problems. Though it is a classic problem, it has, however, not been addressed appropriately. With ME in the location of the vertices of a polygon, the resulting random polygons may undergo complex changes, so that the point-in-polygon problem may become theoretically and practically ill-defined. That is, there is a possibility that we cannot answer whether a random point is inside a random polygon if the polygon is not simple and cannot form a region. For the point-in-triangle problem, however, such a case need not be considered since any triangle always forms an interior or region. To formulate the general point-in-polygon problem in a suitable way, a conditional probability mechanism is first introduced in order to accurately characterize the nature of the problem and establish the basis for further analysis. For the point-in-triangle problem, four quadratic forms in the joint coordinate vectors of a point and the vertices of the triangle are constructed. The probability model for the point-in-triangle problem is then established by the identification of signs of these quadratic form variables. Our basic idea for solving a general point-in-polygon (concave or convex) problem is to convert it into several point-in-triangle problems under a certain condition. By solving each point-in-triangle problem and summing the solutions, the probability model for a general point-in-polygon analysis is constructed. The simplicity of the algebra-based approach is that from using these quadratic forms, we can circumvent the complex geometrical relations between a random point and a random polygon (convex or concave) that one has to deal with in any geometric method when probability is computed. The theoretical arguments are substantiated by simulation experiments.This project was supported by the earmarked grant CUHK 4362/00H of the Hong Kong Research grants Council.     

基于结构光与核线的匹配方法研究

摄影测量与计算机视觉中,同名点的匹配是难点.本文提出基于结构光与核线的同名点匹配方法,简化了对于某些特定物体测量时的匹配问题,方法简单快速,出错率低.本文试验中利用OpenGL模拟无纹理人物头像,用该方法进行立体匹配,取得良好的效果.     

车载纵向摄影影像的核线影像生成与同名点匹配

根据车载纵向摄影影像核线排列的特点，利用相对定向确定立体像对的核线几何关系生成核线影像，并进行同名点匹配，取得了很好的效果。