顾及城区机载LiDAR数据特征的配准算法

条带配准是点云数据处理的一个重要环节.文章介绍了经典ICP配准算法的基本原理;考虑到城区机载LiDAR数据中地物的组成、空间分布等特征,提出了一种ICP算法中对应点集的选择策略,并建立了城区机载LiDAR数据的自动配准流程.利用河南安阳试验场的真实点云数据进行配准实验,结果表明在不需要人工干预的情况下,可以很好地将条带数据拼接在一起,建立无缝点云数据.     

全球导航卫星反射信号的镜面反射点算法

文章从镜面反射点的定义出发,导出了在搜索镜面反射点时应满足的几何条件,分析了目前用于搜索镜面反射点算法的优点及不足;在此基础上,提出了一种二分算法;最后通过双基实验数据对这一算法进行验证,并与其他算法进行对比,结果显示出这种算法在收敛速度、搜索精度以及准确性等方面的优越性.     

基于布尔矩阵的空间关联规则提取方法研究

空间关联规则是空间数据挖掘(SDM)中的重要内容之一。由于空间数据的复杂性,传统的空间关联规则挖掘方法主要是将空间数据库变换为非空间数据库,通过挖掘算法挖掘空间关联规则。目前,Apriori算法是关联规则挖掘中使用最为普遍的算法,但是,由于该算法在关联规则提取过程中需要多次扫描数据库,并且产生冗余的候选项集,因此,在执行大型数据库的关联规则挖掘时,具有效率低下的缺陷。本文基于Apriori算法提出了基于布尔矩阵的空间关联规则挖掘算法,并以挖掘福建省厦门市土地覆盖现状与地形特征因子的空间关联关系作为试验案例,对比Apriori算法的提取结果与提取效率,结果表明:该算法不仅减少了扫描数据库的次数,而且减少了冗余候选项集的产生,提高了空间关联规则的提取效率。     

楼宇内部路径规划算法研究及其应用综述

在人群密集的大型楼宇,构建基于楼宇内部空间三维拓扑结构的逃生疏散路径,是当前路径规划算法研究的难点和热点。本文对当前常见的路径规划算法进行优劣对照比较,并详细阐述其在楼宇内部逃生疏散场景应用的算法思想和主要特征,最后总结了楼宇内部路径规划算法研究的发展方向。     

Forward simulation of coal fire model by transient electromagnetic method with electrical source

Uncontrolled coal fires are natural disasters that may cause mineral loss and environmental damage. The traditional loop source transient electromagnetic method can effectively detect the low-resistivity region of coal fires, but its detection efficiency is not so good for high-resistivity regions. In view of this limitation, a technique based on electrical source transient electromagnetics is proposed in this paper to detect high-resistivity regions in the spontaneous combustion process of coal. Considering the complex geometry of the coal fire area, an unstructured tetrahedral grid is used in this study to realize the spatial discretization of the model, and solve the electromagnetic field based on a vector finite element algorithm. Numerical analysis is used to investigate methods for detecting coal fires and the characteristics of effective anomalies are further examined to provide guidance for practical detection.     

基于QSSP的震源破裂过程反演方法

在Qt平台上,基于QSSP软件,利用C⁺⁺进行地震破裂过程反演方法研究。采用按阶段反演的方法,第1阶段反演采用热浴算法进行全局搜索,先按断层区域的构造背景等初始条件对参数范围进行划取,在该范围内随机给定一组初始值开始迭代,使波形初步拟合避开局部最优解;第2阶段反演使用拟牛顿法进行快速收敛,提高波形拟合程度,迭代至目标函数小于误差条件时停止,输出满足误差条件的待解模型参数。为避免模型参数出现病态问题,使用拉普拉斯方程建立平滑矩阵并引入平滑因子对断层模型进行平滑约束。使用棋盘模型验证该方法的稳定性和可靠性。最后,将全国13个台站的重力数据积分后对2013-04-20芦山7.0级地震的破裂过程进行反演,并与其他研究结论进行对比分析。     

An iterative pressure‐stabilized fractional step algorithm in saturated soil dynamics

This paper presents an iterative, incremental pressure‐stabilized fractional step algorithm for coupled hydro‐mechanical problems with mixed formulations of the displacement–pressure ( u –p) model in saturated soil dynamics that allows the use of finite elements with equal low order of interpolation approximation of u and p. In comparison with the original fractional step algorithm, the distinct features of the proposed algorithm lie in its enhanced stability owing to the introduction of both an iteration procedure and a finite increment calculus (FIC) process into the algorithm. The introduction of the iterative procedure makes the velocity term satisfy the momentum conservation equation in an implicit sense and allows much larger time step sizes to be used than those limited in existing explicit and semi‐implicit versions of the algorithm. The introduction of the FIC process removes the dependence of the stability of the proposed algorithm on the time step size, as a result it allows to using the incremental version of the algorithm and evades the minimum time step size requirement presented in the existing versions of the fractional step algorithm that restricts the application of the algorithm to saturated soil dynamics problems with high frequencies. Numerical experiments demonstrate the effectiveness and improved performance of the proposed iterative pressure‐stabilized fractional step algorithm. Copyright © 2009 John Wiley & Sons, Ltd.     

Multi-objective autocalibration of SWAT model for improved low flow performance for a small snowfed catchment

ABSTRACT

A reliable modelling framework needs to ensure that the model is simulating reality with limited uncertainty, thus enhancing its predictive ability. In the literature, hydrological model assessment using one or more metrics is reported to be inadequate when the river flow regime is required to be reproduced comprehensively. This research is aimed to: (a) calibrate the Soil and Water Assessment Tool (SWAT) based on the concept of multi-objective optimization by applying the Borg multi-objective evolutionary algorithm (MOEA); (b) apply hydrological signatures as objective functions; and (c) adopt a multi-metric approach for model evaluation. The SWAT model was coupled with a relatively newer and powerful Borg MOEA. The inclusion of hydrological signatures as objective functions along with the conventional statistical functions assisted in improving the performance for low flows by 135% in terms of volume efficiency and 65% for flow time series simulation.     

Estimation of Nash's IUH parameters using stochastic search algorithms

In rainfall–runoff studies, it is often necessary to change the duration of a given unit hydrograph. Nash's Instantaneous Unit Hydrograph (IUH) is an ideal method that eliminates the hydrograph duration. This paper presents the results of the application of search algorithms, namely a genetic algorithm and hill climbing, to develop the IUH that minimizes the error between the observed and generated hydrographs. Also the performance of these methods has been compared with that of the classical method used for estimation of IUH, namely the method of moments. The genetic algorithm is a popular search procedure for function optimization that applies the mechanics of natural genetics and natural selection to explore a given search space. Hill climbing is an optimization technique that belongs to the family of local search and algorithms can be used to solve problems that have many solutions, with some solutions better than others. The results obtained from both the genetic algorithm and hill climbing algorithm for estimation of Nash's IUH parameters were compared with the results obtained by the method of moments for storms from two river basins that are located in different climatic regions. It was found that both the genetic algorithm and hill climbing provided improved and consistent results. Copyright © 2008 John Wiley & Sons, Ltd.     

用微机进行Mie散射算法研究

本文介绍在东海微机上用伦茨算法计算Mie级数的系数,其计算程序已运行成功。计算结果表明此法可使误差传播显著减小,计算精度提高,降低了对微机内存客量的要求,同时,本文得到的计算结果与国外公开发表的计算结果达到同样精度。