纹理在铁路线路三维景观动态仿真系统中的应用

介绍了OpenGL中纹理贴图技术的基本概念、性质，结合在铁路线路三维景观动态仿真系统的具体应用，深入剖析了纹理贴图在生成高逼真度的三维模型时的应用方法及技术特点。     

铁路线路三维景观动态仿真系统中纹理的应用

介绍了OpenGL中纹理贴图技术的基本概念、性质，结合在铁路线路三维景观动态仿真系统的具体应用，深入剖析了纹理贴图在生成高逼真度的三维模型时的应用方法及技术特点。     

由矢量等高线数据生成DEM数据的简易方法

当前由等高线数据生成DEM数据的方法大部分都存在算法复杂,实现困难等特点。文章描述了一种通过矢量等高线生成DEM数据的简易方法。通过将等高线网格化然后再进一步进行横向和纵向的插值,生成DEM数据。该方法具有简单易行,适用于精度要求不高的场合。而且对硬件的要求也不高。生成的DEM数据很容易转换成三维模型。     

综合录井井下三维地层可视化建模研究与实现

针对综合录井井下地层特点,采用多层DEM三维可视化模型对地下地质环境进行三维描述,实现综合录井三维地层实时显示.将三维坐标投影转换到二维坐标系中,采用二维Delaunay剖分改进算法构建Delaunay三角网;探讨了剖分后的不规则三角网(TIN)到格网的转换和插值以及通过格网DEM构建三维地层;介绍了根据选择的剖切面方程生成地质体的剖面.系统采用VC++6.0和OPENGL图形接口作为开发平台,可以从任意的角度对剖切开的三维地质体进行观察和分析也能够从任意的角度对三维地质体整体进行观察、缩放和剖切等操作.     

等高线生成DEM以及三维地形建模的研究

文章描述了一种通过等高线生成DEM数据的方法,即先对等高线进行离散化,再进行Delaunay构网然后插值生成DEM数据,并对数据进行三维显示。该方法简单易行,对硬件无较高需求,适用于精度要求不高的场合。     

一种城市三维建模的集成处理方法

在对AutoCAD和MapInfo的数据结构进行分析比较的基础上，首先提出了从CAD图形符合及注记中，提高取程点、高程值以及相关属性信息的面积匹配与类型转换的方法；然后创建了基于CAD线划建筑物的重现点-线拓扑关系生成多边形的方法；最后实现了地形高程与建筑物空间及其属性特征值的自动获取，在此基础上进一步构建了城市DEM模型和实现了三维影象显示，形成了由CAD数据→GIS矢量数据→GIS栅格数据→三维影像的一种城市三维建模的集成处理方法，该方法较之工程化的航空摄影测量方法简单、快速、具有较大的实有价值，另外，还以苏州市32 号街坊的地形数据为例进行了实验，获得了较好的实验结果。     

路线三维建模及三维动画制作

提出了一种构建数字高程模型来描述地形,利用横断面、桥梁、隧道等数据建立路基、桥梁、隧道三维模型,并将地形与这些三维模型拼合在一起形成路线三维模型的方法,在此基础上,通过集成AutoCAD及3DS即可达到对铁路线路进行三维造型的目的。     

铁路线路智能CAD(IRLCAD)系统中的三维景观动态仿真

铁路线路是大地上长大带状建筑物。自然环境和既有的人工建筑对线路走向的规划起着根本性的作用。在计算机上用三维景观动态仿真技术模拟现实环境,让工程师动态地对规划线路经行地区的环境进行观察和分析,从而作出线路走向决策,将是一种理想的设计境界。介绍了铁路线路智能CAD系统中的三维景观动态仿真技术。     

高精度高速度曲面建模的3维地表模拟和漫游算法

三维真实感地形场景是生态系统模拟、虚拟地理环境和三维GIS不可或缺的要素,而高精度高速度曲面建模方法可以动态实时构建高精度曲面模型。论文引入高精度高速度曲面建模方法,提出了一种可以动态生成地表模型并实时绘制和漫游三维真实感地表的方法。该方法实时动态建立高精度DEM,结合改进的视点依赖多分辨率绘制方法,随视点改变动态重建并绘制当前DEM。首先建立当前可见场景的DEM,然后通过依赖于视点的简化等处理建立层次细节模型,进行实时场景绘制和漫游,随视点改变,在当前场景基础上动态加点和减点更新DEM及层次细节模型,生成当前可见场景,以次循环。实例测试表明,算法可产生真实感较强的场景,实时漫游效率较高,模拟精确。     

三维模型任意剖面的程序式凹凸映射生成算法

为解决传统二维凹凸映射无法适用于三维模型任意剖面的问题,提出一种三维模型任意剖面的程序式凹凸映射生成算法。该算法使用球、圆柱等作为模型内部的微观颗粒,使用三维Perlin噪声对颗粒添加扰动,提升模拟真实感。根据颗粒与剖面的位置关系,将剖面分为撕裂面、空心切割面、实心切割面。分别应用不同的程序式凹凸映射算法,计算法线扰动信息,得到剖面的凹凸映射纹理。仿真结果表明,该算法可以在三维模型任意剖面上产生凹凸映射效果,渲染一帧大约只需0.5ms,满足实时切割渲染的需求。     

基于数据库的大地形可视化关键技术研究

地形可视化在GIS、虚拟现实等方面有着广泛应用。论文基于Oracle数据库技术,将DEM数据分块、与视点相关的LOD等技术相结合,采用四叉树遍历高程数据,并给出一种误差控制方法,在PC上实现了对海量地形数据的实时漫游。     

一种高效的Delaunay三角网合并生成技术

在传统的建模方法中，规则三角网方法（GRID）由于是在格网点上对格网周围采样点按照距离远近加权平均，难以在细节上反映原貌，精度不高；不规则三角网方法（TN）按照某种原则（delaunay)将采样点直接民网，建立起模型，但是建模过程复杂，内存耗费很大，当原始采样数据量很大时，效率很低，引进四叉树分块生成标准delaunay网格，并采用凸壳边界跟踪优化合并形成三角网格，大大提高delaunay三角网生成速度，提高了建模效率。     

DEM保真精度定量化描述模型研究

等高线回放法是DEM精度评估的重要方法之一,可以用于检测地形的保真程度,但是现有定量评估指标属于相对保真精度的范畴。因此本文基于水系和地形的固有套合特性,提出了水系和地形套合隶属度函数,从两者的套合程度实现DEM保真精度的定量化描述。首先,根据线状要素位移准则、尺度准则、平均坡度准则、最大套合偏移量准则和目视效果准则,运用模糊数学方法建立水系和地形套合隶属度函数;然后,使用四个不同地貌类型实验区域的1:5万地形图作为基础源数据,实验分析了DEM保真精度的评估。实验结果表明水系和地形套合隶属度函数不仅可以用于DEM保真精度的定量评估,而且可以用于DEM最佳分辨率的确定以及DEM尺度转换的适宜范围的确定。     

DEM保真精度定量化描述模型

等高线回放法是数字高程模型(DEM)精度评估的重要方法之一,可以用于检测地形的保真程度,但是现有定量评估指标属于相对保真精度的范畴,因此基于水系和地形的固有套合特性,提出了水系和地形套合隶属度函数,从两者的套合程度实现DEM保真精度的定量化描述.首先,根据线状要素位移准则、尺度准则、平均坡度准则、最大套合偏移量准则和目视效果准则,运用模糊数学方法建立水系和地形套合隶属度函数;然后,使用4个不同地貌类型实验区域的1∶5万地形图作为基础源数据,实验分析了DEM保真精度的评估.实验结果表明水系和地形套合隶属度函数不仅可以用于DEM保真精度的定量评估,而且可以用于DEM最佳分辨率的确定以及DEM尺度转换适宜范围的确定.     

Evaluation of TanDEM-X 90 m Digital Elevation Model

German Aerospace Center (DLR), EADS Astrium GmbH and Infoterra GmbH alliance came up with the idea of taking DTED-2 (Digital terrain elevation data, level-2) specifications to even higher standard of HRTE-3 (High resolution terrain elevation, level-3) in 2006, as a result TDX (TerraSAR-X, TanDEM-X) constellation was born. The mission was geared to create a rather sensitive, high precision 3 dimensional map of the entire Earth in seamless and very high quality. After Shuttle Radar Topography Mission (SRTM) in 2000 and its derivatives, along with numerous prior and subsequent other similar data, have practically set the standard for defining the topographical surfaces in global scale, the twin satellites acquired all of Earth’s land surfaces numerous times to produce varying resolution digital elevation models (DEM) between 2011 and late 2015. DEMs are widely used in many planning, decision making and engineering related projects. They provide sound backing for mankind’s endeavors. Ground resolution is the most sought after feature of any DEM. Finer resolution is usually associated with a better surface definition. Recently, an entirely new global DEM has been released DLR. The 90 m DEM is the latest variant derived from such an undertaking. This study aimed to examine the overall effectiveness of this alleged new data in four previously surveyed locations and against the performances of finer SRTM 1- and comparable SRTM 3 arc second data. The results showed that TanDEM-X 90 m data overestimated. They seemed to be rather accurate in flat to slightly undulating terrain, but overestimated in broken to treacherous terrain than both SRTMs. Root Mean Square Error was greater in site one and site four, and lower in site two and site three compared to both SRTM 1 and SRTM 3 arc second data.     

Evaluation of terrain effect on microwave radiometer measurement and its correction

We develop a new technique for terrain correction of coarse resolution satellite microwave radiometer measurements using the high-resolution digital elevation model (DEM). With the high-resolution DEM and a facet model, we first simulated the terrain influences that resulted from both effects of local incidence and polarization rotation (PR) on the microwave radiometer measurements at the different scales of the radiometer footprints. The emissivity signals of bare surfaces are more sensitive on incidence and PR than vegetated surfaces. So the emissivities at different incidence angles of the bare surface generated by the advanced integral equation model (AIEM) were used to simulate the terrain effects on the satellite measurements. It was found that (1) the PR effect at the satellite footprint can be corrected using the absolute mean PR angle from all facets within the footprint, and (2) the satellite measurements can be described as from a mean incidence angle. Both angles can be obtained from all facets within the footprint with the high-resolution DEM and the satellite viewing geometry. Therefore, a corresponding terrain-correction technique was developed for satellite brightness temperature measurements. We also demonstrate the terrain effects on the satellite measurements from the advanced microwave scanning radiometer–earth observing system (EOS) (AMSR-E).     

Estimation of average DEM accuracy under linear interpolation considering random error at the nodes of TIN model

The concept of a digital elevation model (DEM) can be used for a digital representation of any single‐valued surface such as a terrain relief model (digital terrain model, DTM). DEMs are widely used in remote sensing, geographical information systems (GIS), and virtual reality. Estimating the accuracy of a DEM is an essential issue in the acquisition of spatial data, particularly for applications that require a highly accurate DEM, such as engineering applications. The accuracy of a DEM is subject to many factors such as the number of sampling points, the spatial distributions of the sampling points, the methods used for interpolating surface elevations, the propagated error from the source data, and other factors. Of these factors, this study will focus on estimating the mean elevation error in a DEM surface that is caused by errors of component nodes in a triangulated irregular network (TIN). This paper will present a newly derived mathematical formula, with the details of the procedure used to derive this formula, to study the relationship between the errors at the TIN nodes and the propagated mean elevation error of a DEM surface that is linearly constructed from the TIN. We have verified the analytical formula by numerical simulation. The experimental results confirm the theoretical derivation of the formula.     

Morphological segmentation of physiographic features from DEM

A terrain can be segmented into three predominant physiographic features; mountains, basins and piedmont slopes. The objective of this paper is to develop a mathematical morphological based algorithm to segment the terrain of a digital elevation model (DEM) into the three predominant physiographic features. Ultimate erosion is used to extract the peaks and pits of the DEM. Conditional dilation is performed on the peaks and pits of the DEM to extract the mountain and basin pixels, respectively. The unclassified pixels are assigned as piedmont slope pixels. The combination of the mountain, basin and piedmont slope regions form the physiographically segmented DEM. The effectiveness of the proposed physiographic segmentation algorithm is tested by implementing it on the Global Digital Elevation Model (GTOPO30) of the Great Basin, Nevada, USA.     

利用雷达摄影测量方法提取DEM及其精度评价

为了解雷达立体摄影测量中各项因素对最终DEM精度的影响,采用马来西亚热带雨林地区具有不同波束模式和入射角的6对Radarsat-1影像,应用两种不同的SAR成像模型,即距离/多普勒模型和等效共线方程模型,对使用雷达摄影测量方法提取DEM进行了试验.首先分析了两种成像模型不同的物理基础,然后通过比较由它们得到的DEM的精度,发现利用距离/多普勒模型提取DEM的精度优于等效共线方程模型;然后,利用研究区的数字地形图等参考资料,分析了不同轨道、不同模式、不同分辨率、不同交角的立体像对组合以及地形因素对DEM精度的影响,要得到高精度的DEM,必须综合考虑立体像对的选取和研究区的地形、地貌等特征.     

由离散点和特征线构建DEM的优化控制方法

基于拉普拉斯方程和优化控制(OC)理论,提出一种构建地形的OC方法.以极小化拉普拉斯方程左端项平方和为目标函数、采样离散点作为等式约束条件、河流线作为不等式约束条件、格网点附近的离散点集的高程范围为上下界约束条件,形成一个标准的OC问题,求解该问题即可获得融合原始数据中隐含信息的数字高程模型(DEM).通过调节OC的参数值,可以获得不同的DEM.实际案例表明,OC方法既能保证地形曲面的整体光滑性,又能保证DEM结果对于原始数据的忠实性,其模拟结果优于约束不规则三角网方法.