Accuracy assessment of digital elevation models by means of robust statistical methods

Measures for the accuracy assessment of Digital Elevation Models (DEMs) are discussed and characteristics of DEMs derived from laser scanning and automated photogrammetry are presented. Such DEMs are very dense and relatively accurate in open terrain. Built-up and wooded areas, however, need automated filtering and classification in order to generate terrain (bare earth) data when Digital Terrain Models (DTMs) have to be produced. Automated processing of the raw data is not always successful. Systematic errors and many outliers at both methods (laser scanning and digital photogrammetry) may therefore be present in the data sets. We discuss requirements for the reference data with respect to accuracy and propose robust statistical methods as accuracy measures. Their use is illustrated by application at four practical examples. It is concluded that measures such as median, normalized median absolute deviation, and sample quantiles should be used in the accuracy assessment of such DEMs. Furthermore, the question is discussed how large a sample size is needed in order to obtain sufficiently precise estimates of the new accuracy measures and relevant formulae are presented.     

多波束数据的海底数字地形模型构建

提出大批量多格式原始多波束数据的DTM构建方法，以满足大区域、大比例尺海底地形制图的需要。在多种格式原始多波束数据接口和系统内部标准数据结构的基础上，通过对数据文件、数据种类和数据运算量的有效组织管理，实施边读入、边权重配赋的网格插值，分析了高斯、指数和距离平方反比权重函数的适用性，及最小值、最大值和平均值的实用性。在权重配赋网格插值基础上，提出分形fBM和张力样条配合使用的方程式插值方法，保证DTM数据的有效外延和地形分辨。整套算法效率高，并能有效保证DTM的精度，对存储在外部介质的数据遍历一次即可完成网格插值。     

平面约束条件在LIDAR点云滤波中的应用

介绍了一种利用平面约束条件对LIDAR点云数据进行滤波的方法,利用每个数据点的邻域点拟合平面,根据平面约束条件和平面点分类方法得到地面点,最后利用地面点内插该区域的DTM.     

基于GIS城市洪水淹没模拟分析

城市洪水淹没范围动态模拟分析是城市防洪规划与防治决策的一个重要基础工作。本文主要研究洪水从翻堤口出发在地理空间蔓延、扩散、动态行进及确定淹没范围的数字模拟方法。为此,根据数学形态学及测地圆概念,研究设计了洪水扩散范围的“膨胀”模拟算法和淹没范围搜索算法,用于查询淹没通块中从翻堤处到任一点之间的淹没路径和ｔ时刻洪水扩散范围。     

香港DTM快速建立的研究

本文论述了建立1：5000香港DTM的基本过程，总结了在DTM生产实践中的技术和管理上所取得的一些经验，对生产中各环节的实际问题提出一些建议，对提高所建立DTM的精度与可用性及提高工作效率，具有一定的意义，为以后各种比例尺的DTM生产提供参考。     

从城市地区的DSM到DTM

讨论了根据影像匹配的结果将ＤＳＭ修正成ＤＴＭ的方法。本文针对城市地区航空影像的立体匹配结果，结合影像的结构纹理特征，提出了一种自动修正影像匹配结果以获得正确的ＤＴＭ的方法。     

Delineation and assessment of Central Indian Suture through lineament extraction approach using Remote Sensing and Geographic Information System

Lineament extraction approach allowed mapping of larger number of lineaments in a classical manner in tectonic and structural studies. In the present study, various techniques were adopted to extract lineaments using Landsat ETM+ images. To remove the biasness of the images, some pre-processing techniques like stream ordering, band differencing, colour texturing were employed to enhance the edges of the structural features. Extracted lineaments and its distribution and orientation were mapped using ArcGIS Spatial analyst tool. Results of the study showed maximum number of lineaments were oriented in the ENE–SWS direction with 63° overall inclination. Accuracy assessment and validation were made with respect to visual interpretation and overlaying the lineament on Digital Topographic Model as well as with respect to an existing geological lineament map of the study site. The result of accuracy assessment indicates higher compatibility of Central Indian Suture with the geological map of the study area.     

用于生成DTM的改进的最小二乘匹配(LSM)算法

本文提供了一种用于生成DTM的LSM算法的数学模型。其特点是,引入了辐射线条件和共面条件的几何约束,以及辐射偏差和几何变形参数的虚拟观测方程。试验表明.改善了LSM算法的收敛性、稳定性和可靠性,因而提高了图像配准的质量。     

Book Reviews

Books reviewed;
D. Fritsch and R. Spiller, Photogrammetric Week '99.
D. R. Wilson, Air Photo Interpretation For Archaeologists
D. R. Green, Gis: A Sourcebook For Schools
R. Gower, Workshop On National Mapping Agencies And The Internet
A. Flotron and O. Koelbl, Precision Terrain Models For Civil Engineering
P. Atkinson and D. Martin, Gis And Geocomputation. Innovations In Gis 7
R. P. Kirby, Revision Measurement Of Large Scale Topographic Data
J. Höhle, Automatic Orientation Of Aerial Images On Database Information
S. Dequal, L. A. Koen and F. Renaudo, Comparison Of National Guidelines For Technical And Cadastral Mapping In Europe ("Ferrara Test")
P. J. Gibson, Introductory Remote Sensing: Principles and Concepts
T. Luhmann, Nahbereichsphotogrammetrie: Grundlagen, Methoden Und Anwendungen     

MAPGIS下重磁数据直接成图的实现及意义

作者在文中介绍了通过编制QBASIC小程序实现两种常见格式重磁数据直接生成MAPGIS图形文件的方法，为其它类似格式数据在MAPGIS下成图及建库提供可借鉴的思路和途径。