基于本体的异构数据集成方法及其实现

分析了传统异构数据集成中存在的困难,给出一个改进的基于本体的异构数据集成方法.该方法采用本体描述信息源领域中的概念,通过构建语义映射关系,解决数据集成中存在的语义异构问题.     

A shadow fraction method for mapping biomass of northern boreal black spruce forests using QuickBird imagery

We have developed and tested a method for mapping above-ground forest biomass of black spruce (Picea mariana (Mill.) B.S.P.) stands in northern boreal forests of eastern Canada. The method uses QuickBird images and applies image processing algorithms to extract tree shadow fraction (SF) as a predictive variable for estimating biomass. Three QuickBird images acquired over three test sites and 108 ground sample plots (GSP) were used to develop and test the method. SF was calculated from the fraction of tree shadow area over the area of a reference square overlaid on the images. Linear regressions between biomass of GSP and SF from the images for each test site resulted in R² in the range from 0.85 to 0.87 (except one case at 0.41), RMSE of 11 to 18 t/ha and bias of 2 to 5 t/ha. Statistical tests demonstrated that local regressions for the three test sites were not statistically significantly different. Consequently, a global regression was calculated with all GSP and produced R², RMSE, and bias of 0.84, 14.2 t/ha and 4.2 t/ha, respectively. While generalization of these results to extended areas of the boreal forest would require further assessment, the SF method provided an efficient means for mapping biomass of black spruce stands for three test areas that are characteristic of the northern boreal forest of eastern Canada (boreal and taiga shield ecozones).     

Remote sensing support for national forest inventories

National forest inventory programs are tasked to produce timely and accurate estimates for a wide range of forest resource variables for a variety of users and applications. Time, cost, and precision constraints cause these programs to seek technological innovations that contribute to measurement and estimation efficiencies and that facilitate the production and distribution of an increasing array of inventory data, estimates, and derived products. Many of the recent innovations have involved remotely sensed data and related statistical estimation techniques. Current applications of remote sensing in support of national forest inventories are reviewed for three areas: (1) observation or measurement, meaning using remotely sensed data in lieu of field observations or measurements; (2) estimation, meaning calculation of traditional inventory areal estimates such as forest area or volume per unit area; and (3) mapping. Future applications focus on two areas: augmenting field measurements with remotely sensed data obtained from lidar sensors and Internet accessible map-based estimation.     

Development of an Elastoviscoplastic Microstructural-Based Continuum Model to Predict Permanent Deformation in Hot Mix Asphalt

Permanent deformation in hot mix asphalt is caused by a combination of densification (decrease in volume and hence increase in density) and shear deformation. The primary objective of this paper is to develop an elastoviscoplastic model that accounts for the influence of important microstructure properties such as anisotropy and damage on permanent deformation. The model incorporates a yield surface based on the Drucker-Prager function that is modified to capture the influence of stress state on the material response. Also, parameters that reflect the directional distribution of aggregates and damage density in the microstructure are included in this yield surface model. The elastoviscoplastic model is converted into a numerical formulation and is implemented in finite element (FE). The FE model is used in this study to simulate experimental measurements under different confining pressures and strain rates.     

虚拟地形建模及运动目标实时监测的研究

随着虚拟现实技术、3S技术、网络技术的发展,地形三维可视化和目标监测等方面已成为研究的热点。该文结合开发的应用系统论述了实现地球三维可视化的建模方法,以及Internet环境下在三维虚拟地形上实现目标监测的技术。     

对象/关系映射框架的研究与应用

在软件工程的各个阶段运用并体现面向对象的思想,已经成为软件设计开发的主旋律。占主导地位的关系数据库成为了面向对象系统架构中对象与关系数据库转换的“瓶颈”。论文着眼于面向对象系统中的类及其实例与关系数据库中表的映射,分析了类及其实例与关系数据库的映射模型,比较了几种映射解决方案的优缺点,重点研究了Castor在O/R(对象/关系)映射方面的优势及应用。     

Consideration of the errors inherent in mapping historical glacier positions in Austria from the ground and space (1893-2001)

The historical record of in situ measurements of the terminus positions of the Pasterze and Kleines Fleißkees glaciers in the eastern Alps of Austria is used to assess uncertainties in the measurement of decadal scale changes using satellite data. Topographic maps beginning in 1893, and satellite data from 1976 to 2001, were studied in concert with ground measurements to measure glacier changes. Ground measurements show that the tongue of the Pasterze Glacier receded ∼1150 m from 1893 to 2001, while satellite-derived measurements, using August 2001 Landsat Enhanced Thematic Mapper Plus (ETM+) data registered to an 1893 topographic map, show a recession of 1300-1800 m, with an unknown error. The measurement accuracy depends on the registration technique and the pixel resolution of the sensor when two satellite images are used. When using topographic maps, an additional source of error is the accuracy of the glacier position shown on the map. Between 1976 and 2001, Landsat-derived measurements show a recession of the terminus of the Pasterze Glacier of 479±136 m (at an average rate of 19.1 m a⁻¹) while measurements from the ground showed a recession of 428 m (at an average rate of 17.1 m a⁻¹). Four-meter resolution Ikonos satellite images from 2000 and 2001 reveal a shrinkage of 22,096±46 m² in the Pasterze tongue. The nearby Kleines Fleißkees glacier lost 30% of its area between 1984 and 2001, and the area of exposed ice increased by 0.44±0.0023 km², according to Landsat satellite measurements. As more recent satellite images are utilized, especially data that are geocoded, the uncertainty associated with measuring glacier changes has decreased. It is not possible to assess the uncertainty when an old topographic map and a satellite image are coregistered.     

端口守护进程的研究与实现:同时支持IPv4与IPv6协议栈

讨论了IPv4网络与IPv6网络之间的互操作及平滑升级机制。阐述了守护进程运行原理,IPv6服务器与IPv6,IPv4客户端进行通信的原理。讨论了基于端口守护进程实现双协议栈支持的技术方案,并在Linux环境下实现了一个端口守护进程,能够同时支持IPv4与IPv6协议栈。     

基于多XML文档的政务数据交换平台构造及实现

基于多XML文档的政务数据交换平台以映射函数作为基本计算单位，将XML数据交换操作分解为数据抽取、函数及数据组合3个步骤，通过映射函数的组合实现复杂的XML数据交换操作。相对目前采用XSLT技术进行XML文档格式转换的方式，该平台具有开发效率高、可扩育性强等优点。     

基于Java技术的WebGIS框架研究

本文力图把当前软件开发技术和Java技术领域中逐渐成熟的设计模式和方法,引入到WebGIS基础开发框架的设计中,以提高框架的可设计性和简化应用开发;表现层中引入MVC模式,数据访问层使用对象一关系映射技术,逻辑层提供有关空间操作的Java APIs(Java Application Program-ming Interface).以此作为框架的基本组成单元.基于Java平台对这个框架的原型进行了实现。以期能为WebGIS框架设计提供一个有意义的参考实现。