三维激光扫描技术曲面拟合方法研究

点云数据处理以及点云的曲面、曲线拟合是逆向工程中一个重要的研究课题,其重要任务就是将实际物理模型重建生成几何模型,而核心问题就是如何从采样点出发重建曲线、曲面模型。本文以C++开发平台和MATLAB为基础,对三维激光扫描数据利用B样条、NURBS、三角网格曲面拟合方法和曲线拟合方法进行研究探索。     

基于GPGPU技术快速提取数字表面模型

介绍一种基于通用计算图形处理单元（GPGPU）技术快速提取数字表面模型（DSM）的方法,探讨了使用LiDAR和摄影测量方法获取数字表面模型的不同特点,并通过分别使用CPU和GPU技术获取一个大面积山区数字表面模型的案例对比,证明了基于CUDA架构的数字表面模型提取方法是有效和可行的。     

基于支漳河治理的工程测量设计

本文在对支漳河研究的背景下,结合所学工程测量知识,从测区概况、外业实测、内业设计等方面进行阐述,并进行了土方计算、曲线放样的设计,为支漳河治理的实施提供理论依据。     

横向非均匀介质多道瑞雷波频散曲线正演

作为近地表横波速度结构成像的主要手段之一,面波多道分析法的正问题研究对现场观测系统设计及后续反演计算具有重要意义.目前面波频散曲线的正演主要分为两类:一是对水平层状介质中面波的本征值问题进行求解,该类方法计算效率高但较难考虑地下介质在横向上的不均匀性;二是基于波动方程的全波场模拟,该类方法在理论上可考虑任意复杂的地质模型但计算成本相对较高.本文基于振幅归一化加权的聚束分析,提出了一种适用于横向非均匀介质模型的多道瑞雷波频散曲线正演方法.首先,基于聚束分析的计算公式推导得到了经振幅归一化加权后输出功率谱中相速度与局部相速度之间的关系,然后通过黄金分割极值搜索算法计算得到了多道瑞雷波数据的理论频散曲线.数值分析结果表明,该算法能够快速地实现横向非均匀介质中多道瑞雷波频散曲线的正演计算,所求取的频散曲线与采用二维弹性波时间域有限差分模拟分析得到的结果误差较小,这在一定程度上说明了该计算方法的可靠性,从而可为面波多道分析法中的观测系统快速优化设计以及横向非均匀介质中频散曲线的反演解释提供理论支撑.     

遥感影像边缘灰度分布函数研究

通过正态分布函数、反正切分布函数和二次有理分式函数分析了边缘灰度分布的变化特征,力图找出精度更高、速度更快的边缘定位方法 ;用3种函数对灰度图像和彩色图像边缘进行了定位分析。实验证明,反正切函数具有较高的精度,运算速度更快,可广泛应用于海量遥感影像边缘提取。     

ParSymG: a parallel clustering approach for unsupervised classification of remotely sensed imagery

ABSTRACT

Symmetry is a common feature in the real world. It may be used to improve a classification by using the point symmetry-based distance as a measure of clustering. However, it is time consuming to calculate the point symmetry-based distance. Although an efficient parallel point symmetry-based K-means algorithm (ParSym) has been propsed to overcome this limitation, ParSym may get stuck in sub-optimal solutions due to the K-means technique it used. In this study, we proposed a novel parallel point symmetry-based genetic clustering (ParSymG) algorithm for unsupervised classification. The genetic algorithm was introduced to overcome the sub-optimization problem caused by inappropriate selection of initial centroids in ParSym. A message passing interface (MPI) was used to implement the distributed master–slave paradigm. To make the algorithm more time-efficient, a three-phase speedup strategy was adopted for population initialization, image partition, and kd-tree structure-based nearest neighbor searching. The advantages of ParSymG over existing ParSym and parallel K-means (PKM) alogithms were demonstrated through case studies using three different types of remotely sensed images. Results in speedup and time gain proved the excellent scalability of the ParSymG algorithm.     

Development of fragility curves using high‐dimensional model representation

Fragility curves represent the conditional probability that a structure's response may exceed the performance limit for a given ground motion intensity. Conventional methods for computing building fragilities are either based on statistical extrapolation of detailed analyses on one or two specific buildings or make use of Monte Carlo simulation with these models. However, the Monte Carlo technique usually requires a relatively large number of simulations to obtain a sufficiently reliable estimate of the fragilities, and it is computationally expensive and time consuming to simulate the required thousands of time history analyses. In this paper, high‐dimensional model representation based response surface method together with the Monte Carlo simulation is used to develop the fragility curve, which is then compared with that obtained by using Latin hypercube sampling. It is used to replace the algorithmic performance‐function with an explicit functional relationship, fitting a functional approximation, thereby reducing the number of expensive numerical analyses. After the functional approximation has been made, Monte Carlo simulation is used to obtain the fragility curve of the system. Copyright © 2012 John Wiley & Sons, Ltd.     

Author index 2000

Abstract

Both the conventional and the Carlson trophic state index (TSI) classification methods were employed to assess the eutrophication state of 26 lakes in the Norfolk Broads, UK. The parameters employed were: Secchi depth, chlorophyll a and total phosphorous which had been obtained previously by using Landsat TM imagery, ground reference data and empirical algorithms for the Norfolk Broads (Baban, 1993). The conventional method did not provide sufficient differentiation between the Broads. The Carlson TSI provided sufficient information to differentiate between all 26 Broads. Consequently, using the Carlson TSI information, these Broads were classified into three groups. The classification was based on the relationship between the calculated Carlson TSI of the external phosphorous loading and its influence on the eutrophication process as deduced from the calculated TSI values for the other two parameters. The results were consistent with all the available knowledge and experience concerning these Broads and demonstrated the potential of combining remote sensing techniques and Carlson TSI in eutrophication assessment, ecosystem checking and watershed analysis.     

自然伽马拟声波曲线构建技术探讨

声波测井曲线在地震反演中起着约束和控制模型反演的作用,当其不能反映地层岩性变化时,通常会将现有的非声波测井曲线按照一定的经验公式或统计方法来重构新的声波曲线。但是,这些拟声波曲线构建技术并没有考虑到地层岩石孔隙及孔隙中流体的影响。在考虑到岩石孔隙和孔隙中流体的情况下,拟声波曲线构建技术可以先利用岩石基质的声波速度与自然伽马之间的关系来重构具有声波量纲的新曲线,然后结合原声波曲线中能够反映背景速度的低频信息,构建出新的声波曲线。该方法在鄂尔多斯盆地镇泾地区取得了不错的应用效果。