A New 3‐D Solar Radiation Model for 3‐D City Models

Estimates of solar radiation distribution in urban areas are often limited by the complexity of urban environments. These limitations arise from spatial structures such as buildings and trees that affect spatial and temporal distributions of solar fluxes over urban surfaces. The traditional solar radiation models implemented in GIS can address this problem only partially. They can be adequately used only for 2‐D surfaces such as terrain and rooftops. However, vertical surfaces, such as facades, require a 3‐D approach. This study presents a new 3‐D solar radiation model for urban areas represented by 3‐D city models. The v.sun module implemented in GRASS GIS is based on the existing solar radiation methodology used in the topographic r.sun model with a new capability to process 3‐D vector data representing complex urban environments. The calculation procedure is based on the combined vector‐voxel approach segmenting the 3‐D vector objects to smaller polygon elements according to a voxel data structure of the volume region. The shadowing effects of surrounding objects are considered using a unique shadowing algorithm. The proposed model has been applied to the sample urban area with results showing strong spatial and temporal variations of solar radiation flows over complex urban surfaces.     

基于三棱柱的三维地质体建模及可视化研究

建立可视化的三维地质模型是地质信息可视化的一个研究重点,能够为各种地质现象描述提供科学依据。本文主要研究了基于三棱柱的模型构造,提出了三棱柱的改进数据结构和切割的构形以及算法,并且在VC6.0环境下,采用OpenGL作为图形开发工具,实现了三维地质体的可视化,解决了地质体剖切和基坑开挖等问题。     

浅谈基于ArcGIS的三维可视化系统实现

将ArcGIS作为基础平台,以面向对象的思想原理为基础,对相对规则的实体对象进行了三维重建。考虑到三维平台模型缺乏真实感,在用传统三维建模的基础上,实现了对三维模型的创建并巧妙地将得到的模型转换为GIS可以处理利用的数据格式,进而依此实现对三维GIS系统的开发。     

Development and Application of 2D and 3D GRASS Modules for Simulation of Thermally Driven Slope Winds

The ability to manage and process fully three‐dimensional information has only recently been made available for a few Geographical Information Systems (GIS). An example of integrated and complementary use of 2D and 3D GRASS modules for the evaluation and representation of thermally induced slope winds over complex terrain is presented. The analytic solution provided by Prandtl (1942) to evaluate wind velocity and (potential) temperature anomaly induced by either diurnal heating or nocturnal cooling on a constant angle slope is adopted to evaluate wind and temperature profiles at any point over both idealised and real complex terrain. As these quantities depend on the slope angle of the ground and on the distance from the slope surface suitable procedures are introduced to determine the coordinate n of a point in the 3D volume measured along the direction locally normal to the terrain surface. A new GRASS module has been developed to evaluate this quantity and to generate a 3D raster file where each cell is assigned the value of the cell on the surface belonging to the normal vector. The application of the algorithm implemented in GRASS to an ideal valley and to a real valley close to the city of Trento in the Alps provides results in accordance with data reported in the literature. An extension of Prandtl's (1942) model to take into account humidity and evaporation processes on the soil is also proposed and implemented.     

平面随机线元等概率密度误差模型边界包络线

线状实体误差模型包络线既是GIS位置不确定性研究的重要内容,又是GIS可视化研究的关键指标.为了充分利用计算机技术求解符合GIS精度要求的误差模型包络线,基于文献[1,2]中探讨过的等概率密度误差模型建模机理和数值算法,研究了平面随机线元等概率密度误差模型边界包络线的确定原理和计算方法,并通过实例辅以可视化分析,验证了原理的正确性和可操作性.     

基于钻孔数据的地层三维可视化改进算法

地层可视化是三维GIS在地学中的一个重要应用。针对矿山特性,在综合前人研究成果的基础上,给出了一种由工程钻孔数据构建三维地层模型的方法,同时改进了构建地层的三角格网生成算法,提高了三角格网的生成速度,并通过一个建模实例展示了该方法的实际建模效果。     

树模型的三维可视化研究

树的表达无论是在3DGIS，VRGIS还是在3DCM中，都是一个难点问题。与一般实体对象不同的是，树明显具有分形空间特征，因此用常规简单的建模方法很难表达一颗树。现在分形算法常用来生成树模型，具有逼真的可视效果，但所产生的数据量对于GIS环境来说太大，可视化困难；另外，用树的图像替代树模型也是一种常用的方法，但在近视点视觉效果差，同时也没有表达出树木所固有的空间特征。本文作者提出一种方法，使用LOD技术，将树的分形模型与其图像替代模型两者结合起来，初步解决树模型在GIS中的可视化问题，可达到逼真、高速的可视效果。     

基于三棱柱的地质体三维交互应用研究

三维交互应用研究是3DGM领域面向应用的研究重点,能够充分展示地质体的三维空间属性,具有重要的实践意义。本文以三棱柱作为基本体元进行建模,讨论了虚拟钻探、虚拟地质剖面、虚拟开挖、虚拟漫游四种在地质领域的应用算法,并且采用VC++和OpenGL作为开发平台模拟实现,解决了工程实践中的一些实际问题。     

Using fuzzy logic for modeling aquifer architecture

Modeling the geologic architecture of an aquifer and visualizing its three-dimensional structure require lithologic data recorded during well drilling. Uncertainties in layer boundaries arise due to questionable quality of drilling records, mixing during the drilling process, which results in blurred contacts, and natural heterogeneity of the geologic materials. An approach for modeling and visualizing the spatial distribution of aquifer units three-dimensionally based on fuzzy set theory is developed. An indicator is defined for evaluating the possibility of aquifer existence based on fuzzy set theory and probability principles. A specific interpolation method for aquifer 3D spatial distribution requiring only very basic borehole log data is proposed. A 3D modeling and visualization system for aquifers is also developed, which can implement basic GIS functions, like borehole identification and cross-section creation. The methodology developed is tested using real borehole lithology data available for an aquifer in British Columbia, Canada.

---

基于Java/Java 3D的地层3维建模与可视化

利用Java 3D技术建立一个地层可视化3维建模系统,实现地层3维模型漫游、旋转、剖切等功能,并以某地区地下水资源调查评价中采集的地质钻孔数据为例,验证该系统的有效性。该系统将不仅为地下水模型的3维实体建模提供理论支持,而且将推动WebGIS在地下水模型中的应用。     

CAUSTA: Clifford Algebra‐based Unified Spatio‐Temporal Analysis

Introducing Clifford algebra as the mathematical foundation, a unified spatio‐temporal data model and hierarchical spatio‐temporal index are constructed by linking basic data objects, like pointclouds and Spatio‐Temporal Hyper Cubes of different dimensions, within the multivector structure of Clifford algebra. The transformation from geographic space into homogeneous and conformal space means that geometric, metric and many other kinds of operators of Clifford algebra can be implemented and we then design the shortest path, high‐dimensional Voronoi and unified spatial‐temporal process analyses with spacetime algebra. Tests with real world data suggest these traditional GIS analysis algorithms can be extended and constructed under Clifford Algebra framework, which can accommodate multiple dimensions. The prototype software system CAUSTA (Clifford Algebra based Unified Spatial‐Temporal Analysis) provides a useful tool for investigating and modeling the distribution characteristics and dynamic process of complex geographical phenomena under the unified spatio‐temporal structure.     

3D GIS技术研究发展综述

回顾了3DGIS的发展进程,从三维空间数据获取,三维数据模型,三维空间数据管理和分析以及三维可视化技术4个方面综述了3DGIS技术的发展。探讨了目前研究3DGIS的4个热点问题:①数据源集成快速获取数据的方法;②不同数据模型的集成;③支持空间分析的面向对象的数据模型;④城市三维模型。     

浅谈OpenGL在地学3维可视化中的应用

3维地形模型无论是在直观的视觉感受还是在空间分析等方面都是2维地学模型所无法比拟的。DEM是建立地学3维可视化的主要内容,也是3维地理信息系统GIS的主要研究内容之一。本文所实现的程序是在VC 6.0平台基础上,基于DEM数据,利用OpenGL提供的相关功能函数,达到地学3维可视化的目的,同时利用纹理映射技术为3维模型贴纹理建立真实感强的3维环境。     

Integrating GIS‐Based Geo‐Atom Theory and Voxel Automata to Simulate the Dispersal of Airborne Pollutants

Environmental processes are usually conceptualized as complex systems whose dynamics are best understood by examining the relationships and interactions of their constituent parts. The cellular automata paradigm, as a bottom‐up modeling approach, has been widely used to study the macroscopic behavior of these complex natural processes. However, the cellular automata models are largely restricted to the two‐dimensional spatial perspective even though the process dynamics they represent evolve in the three spatial dimensions. The objective of this study is to develop a voxel‐based automata approach for modeling the propagation of airborne pollutants in three‐dimensional space over time. The GIS‐based geo‐atom theory was used to manage the data within the automaton. The simulation results indicate the model has the capability to generate effective four‐dimensional (4D) simulations from simple transition rules that describe the processes of particle advection and diffusion. The application of voxel‐based automata and the geo‐atom concepts allows for a detailed 4D analysis and tracking of the changes in the voxel space at every time‐step. The proposed modeling approach provides new means to examine the relationships between pattern and process in 4D.     

GIS中平面一般曲线误差模型包络线

误差模型包络线是GIS位置不确定性研究的重要内容,是GIS可视化研究的关键指标.为了充分利用计算机技术求解符合GIS精度要求的包络线,以不规则曲线为例,叙述基于数值算法的一般曲线误差模型包络线的确定原理和计算方法,并通过实例进行可视化分析,验证原理的正确性和可操作性.     

GIS三维建模技术在镇江市体育会展中心岩土工程中的应用

本文介绍了GIS三维地形建模技术的常用方法,利用ArcGIS平台三维分析扩展模块建立一个三维地形模型。模型为该项岩土工程的建设提供了真实、客观的可视化参考数据,对本次岩土工程的建设起到了重要作用。     

Geometric Parameters as Key Factors for the 3D-modeling of Fluvial Deposits

GIS is an established and appropriate tool for the management and evaluation of geodata which is being increasingly used for the three‐dimensional modeling of strata. An advanced technique for the GIS‐based 3D‐modeling is developed here in order to integrate genetic aspects of deposition into the modeling process. The ArcView^® software (ESRI, Inc., Redlands, California) and the extensions 3D‐Analyst and Spatial Analyst have been used for the data management and layer rendering. The tools VirGIL and GSI‐3D (Insight Corp., Germany) have been applied for the purpose of visualization of the layers in 3D. The main topic of the work is the generation of geometrically consistent models of fluvial terrace bodies, which represent monogenetic fills of Pleistocene palaeovalleys. One peculiarity of the investigated Illerglacier foreland, southern Germany, is the occurrence of highly eroded terrace remnants. The preserved deposits are tied to several accumulation levels, but the usual way of morphostratigraphic interpretation is limited and results in lots of different stratigraphies and palaeogeographic ideas presented in literature. The sediment fill of meltwater valleys, which can be identified in the Illerglacier area is reconstructed based upon intense field mapping. The terrace accumulations are defined by the base and surface layers, which are thought to be isochronous. Some 1,400 data points were used to model these layers in 3D. The geometry of the sediment deposits is defined using basic parameters, e.g. the gradient and the thickness of the terrace, which are used as bench levels for the modeling process. The quality of the calculated maps and cross‐sections far surpasses that of those derived in the classic way without a genetic concept and without using the 3D‐modeling technique. The results derived from the terrace models are relevant for the stratigraphy and palaeogeography of the investigated region of the Alpine foreland. The advanced modeling technique can be used for the detail analyses of terrace sequences of other regions.     

Total 3D‐viewshed Map: Quantifying the Visible Volume in Digital Elevation Models

The 3D perception of the human eye is more impressive in irregular land surfaces than in flat land surfaces. The quantification of this perception would be very useful in many applications. This article presents the first approach to determining the visible volume, which we call the 3D‐viewshed, in each and all the points of a DEM (Digital Elevation Model). Most previous visibility algorithms in GIS (Geographic Information Systems) are based on the concept of a 2D‐viewshed, which determines the number of points that can be seen from an observer in a DEM. Extending such a 2D‐viewshed to 3D space, then to all the DEM‐points, is too expensive computationally since the viewshed computation per se is costly. In this work, we propose the first approach to compute a new visibility metric that quantifies the visible volume from every point of a DEM. In particular, we developed an efficient algorithm with a high data and calculation re‐utilization. This article presents the first total‐3D‐viewshed maps together with validation results and comparative analysis. Using our highly scalable parallel algorithm to compute the total‐3D‐viewshed of a DEM with 4 million points on a Xeon Processor E5‐2698 takes only 1.3 minutes.     

A Hybrid System of Expanding 2D GIS into 3D Space

A hybrid system that integrates two-dimensional (2D) GIS and three-dimensional (3D) visualization has been developed to provide unique solutions to application domains where traditional 2D GIS and 3D visualization cannot alone provide a solution. In this paper, we focus on three key issues in realizing such an integrated system, including large-scale terrain rendering, 2D and 3D combination display (for example, rendering 2D GIS layers in 3D space), expanding traditional 2D GIS analysis functions into a 3D environment, and visualizing 3D geographical data. A generic framework is developed to integrate 3D visualization with various types of 2D GIS, such as commercial GIS software, open source GIS software and spatial databases. A prototype 2D and 3D hybrid system that seamlessly integrates 2D GIS (developed with ArcEngine) and 3D rendering engine (developed with DirectX) is then developed based on the framework. In this hybrid system, 2D and 3D data are viewed within the same scene. Multiple 2D GIS layers are overlaid on the base terrain using a Level of Detail (LOD) model. Advanced query functions, data accessing, data management and spatial analysis, which are executed in the traditional 2D GIS, are provided to users in a 3D environment by continuously transforming information between the 2D GIS subsystem and the 3D subsystem. The 3D data are organized and displayed by Keyhole Markup Language (KML) and textured 3D models in the COLLAborative Design Activity (COLLADA) format. The prototype demonstrates that this hybrid system has effectively addressed the three key issues identified above and that it can seamlessly integrate 2D GIS and 3D visualization. The hybrid system has great potential to be employed in many application domains, such as urban planning, landscape design and environmental decision making, among others, to enhance the 3D design capability and facilitate public participation in the planning, design and decision-making process.     

基于OGRE的高精度三维城市建模技术分析

三维城市模型作为城市三维地理信息系统的重要组成部分,已广泛应用于城市规划、城市建设、建筑设计等领域。随着计算机图形学技术以及虚拟现实技术的不断发展,为快速、自动化生成高精度的三维城市模型提供了条件。本文基于OGRE引擎,阐述了三维城市建模技术的整体架构及关键技术,开发了自动化建模工具及三维可视化平台,实现了城市建筑自动建模及模型实时渲染显示。