基于时态数据库技术的导航信息空间关系局部动态更新方法

针对目前导航电子地图生产中导航地图数据生产周期长的问题,提出了一种基于导航数据生命周期状态维护触发器的导航地图数据生产时空动态更新模型。首先基于时空数据库技术构建了导航地图数据生产时空数据模型,构建了导航数据生命周期状态维护触发器,将导航数据空间关系分为一级几何拓扑和二级逻辑拓扑。利用触发器,使得导航数据的任何变更（几何和逻辑）得到有效记录,保证了增量包的有效导出。     

Terrestrial laser scanning to estimate plot-level forest canopy fuel properties

This paper evaluates the potential of a terrestrial laser scanner (TLS) to characterize forest canopy fuel characteristics at plot level. Several canopy properties, namely canopy height, canopy cover, canopy base height and fuel strata gap were estimated. Different approaches were tested to avoid the effect of canopy shadowing on canopy height estimation caused by deployment of the TLS below the canopy. Estimation of canopy height using a grid approach provided a coefficient of determination of R² = 0.81 and an RMSE of 2.47 m. A similar RMSE was obtained using the 99th percentile of the height distribution of the highest points, representing the 1% of the data, although the coefficient of determination was lower (R² = 0.70). Canopy cover (CC) was estimated as a function of the occupied cells of a grid superimposed upon the TLS point clouds. It was found that CC estimates were dependent on the cell size selected, with 3 cm being the optimum resolution for this study. The effect of the zenith view angle on CC estimates was also analyzed. A simple method was developed to estimate canopy base height from the vegetation vertical profiles derived from an occupied/non-occupied voxels approach. Canopy base height was estimated with an RMSE of 3.09 m and an R² = 0.86. Terrestrial laser scanning also provides a unique opportunity to estimate the fuel strata gap (FSG), which has not been previously derived from remotely sensed data. The FSG was also derived from the vegetation vertical profile with an RMSE of 1.53 m and an R² = 0.87.     

长度检定场设计及控制测量

长度检定场是电磁波测距仪量值传递的主要标准,主要用于各等级电磁波测距仪的常数测定,本文根据相关的测量规范,就建场设计及其控制测量中一些技术问题作了一些分析和探讨.     

土地利用现状图的矢量化方法研究

土地利用现状图的数字化是建立土地利用数据库的主要技术手段之一,图斑作为土地利用现状图的主要要素,其矢量化方法的优化与否不仅关系着整个数据采集的进程,而且还将影响到土地信息系统的稳定与否。文章针对传统的图斑矢量化引起的面域交叉、对象撕裂等问题研究提出了基于弧段的图斑矢量化方法,并通过线状地物与图斑的叠合分析,建立线状地物...     

基于不同类型底图的旅游地图符号设计

作为一种现代生活时尚中的旅游工具,旅游地图种类多样,需求量大。本文分析了旅游地图不同类型底图的表示特点和相互差异,探讨了不同类型底图上旅游地图符号的设计原则和方法,为更好地设计和制作旅游地图提供了依据。     

大比例尺土地利用数据库建设有关技术问题的探讨

地籍调查、村集体土地所有权调查和土地利用调查对调查底图的要求不同,在土地利用数据库建设的过程中应综合考虑;GPS、GIS和RS技术的应用,改变了土地利用调查的技术流程,提高了调查效率;土地利用数据库质量控制包括质量检查方法、质量标准和质量责任体系。     

基于ArcGIS的面状要素中轴线提取方法研究

专题制图中利用遥感技术获取专题要素和地理底图要素已成为大势所趋,而如何实现面状要素中轴线的提取从而获得线状道路、线状河流等底图要素一直是GIS界研究的热点。本文通过对ArcGIS9.0中提供的各种功能模块的综合应用实现了面状要素中轴线的自动提取。经实验这种方法简单实用、效果理想,效率很高。     

浅谈全国第二次土地调查项目的几个关键环节

介绍了全国第二次土地调查项目中调绘底图生产、土地调查、田坎系数测定、农村宅基地调查等关键环节,结合实际生产,分析了各环节的重要性及实施情况。     

《测量学》教学实习的改革与实践

介绍了９５年至今我们对土建类专业测量教学实习的改革措施和积累的经验,它对相关专业的测量教学实习有一定的参考意义。     

Interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane

The complex variables boundary element method (CVBEM) is used to study interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane. A new complex hypersingular equation for piecewise homogeneous media with a circular opening is obtained. The equation is solved using the CVBEM technique with circular and straight boundary elements and polynomial approximations (with square root asymptotics for crack tip elements) for the unknown functions. The algorithm is verified through comparison with known semi‐analytical and numerical solutions that involve interaction between a circular opening and specific systems of cracks or other openings. New numerical results concerning the interaction of the circular opening with the cracks and circular inclusions are presented. The method is applied to an important problem in the petroleum industry: modelling propagation of hydraulic fractures in the vicinity of a borehole. Copyright © 2000 John Wiley & Sons, Ltd.