用于ROAM算法优化的三角形条生成方法

三维地形模型的生成与显示是建模与仿真领域的一个重要研究内容．研究了使用三角形条对ROAM算法进行优化,得到了一种适用于实时运行的视点相关多分辨率地形模型生成算法,对地形的建模、与地形相关研究及地形实时可视化渲染等问题的解决具有实际意义．     

基于小波分析的多分辨率地形构建

地形建模是虚拟战场构建的一个重要方面,DEM和正射影像是地形可视化的主要数据来源,他们可看作是表示地形信息的二维信号。首先论述了小波分析的基本原理,利用多次二进制小波对DEM和影像进行压缩,构建了一个多分辨率地形模型。实践证明,该方法具有压缩比高、压缩速度快等优点,同时还解决了不同分辨率子块之间的"裂缝"问题,可以满足大规模地形数据实时无缝漫游的需要。     

GeoTIFF遥感图像在Unreal Engine中的应用

Unreal Engine是目前世界上顶级的游戏引擎,其在制作地形模型方面功能强大,但要制作真实地形模型时就需要遥感图像的支持.GeoTIFF是TIFF图像格式的一种扩展,它含有位置、高程、映射关系等地理信息.本文首先简要介绍了UE地形编辑器和GeoTIFF图像的格式.随后我们将GeoTIFF遥感图像转换为UE地形编辑器需要的16位PNG格式图像,将PNG格式图像导入到UE地形编辑器后,UE地形编辑器生成了具有真实位置和高程信息的地形模型.同时我们对该过程中遇到的几个关键问题给出了解决办法.     

基于MATLAB提取数字地图的电波传播问题研究

在抛物方程的基础上引入了地形高程剖面,预测了复杂地形条件下的电波传播特性.首先,基于MATLAB提取调用了数字地图,给出了其主要程序流程图以及提取调用的方法,之后采用插值方法增加了地形模型与实际地形剖面的契合度;其次,使用MATLAB的GUI功能设置了一个高程剖面系统,该系统能够提取地球上任意两点之间的地形高程剖面;最后,通过将高程剖面系统提取的地形高程剖面加入到抛物方程模型中进行计算,分析了在复杂地形环境下电波传播的特性.     

基于GIS战场环境传感信息的可视化研究

现有的地理信息系统仅给出了地形、地貌数据,不能满足雷达、红外等传感器成像仿真的需要.基于此本文提出了一种在建立地形、地貌及其战场环境传感信息基础上,利用雷达、红外传感器对战场环境进行可视化仿真的方法.该方法首先是在分析地理信息系统的前提下,讨论了战场地形模型的建立方法,并给出了战场人文目标模型的建模技术,建立了战场地形...     

基于分形和高度图控制的三维地形生成技术研究

介绍了分形理论,论述了使用随机布朗运动和中点位移法生成地形的过程及其不足,并在分形理论的基础上提出了一种基于中点位移法和高度面控制混合的随机地形生成方法,介绍了对地形模型进行纹理贴图的方法及其实现,最后给出利用该方法生成随机地形的实例.     

基于ROAM算法的数字地面模型研究与实现

针对规则网格的数据量过大问题,采用了基于分块的ROAM算法进行多分辨率渲染,根据地形粗糙程度和视点位置,对地形进行有选择的细化,将庞大的三角形二叉树分为多个小二叉树,提高了地形构建效率,在此基础上建立地物要素模型,完成了数字地面模型的构建与多分辨率渲染.     

航向台电磁信号覆盖分析系统设计

由于航向台电磁辐射场的有效覆盖范围与其部署的海拔高度、周边地形条件存在密切关系，因此，针对航向台周围的地形环境，设计了 LOC 天线模型，搭建了高性能 GIS 平台， 构建了基于 SRTM 数据的高程数字地形模型，并结合无线电信号传输模型和衰减模型，运用 Deygout 算法预测无线电在地形遮蔽下的衍射损耗值，最后实现了对航向台无线电在地形下的覆盖范围仿真评估系统的软件设计，该软件可对航向台无线电的有效覆盖范围进行仿真分析评估。     

三维地形在虚拟现实中的建模与算法研究

虚拟现实中地表模型的应用,三维建模的应用更是提供了较高的刷新频率,将海量数据地形实时显示问题有效解决,做好地形建模多分辨模型的建立,实现高度真实感三维地形的构造。文章通过结合虚拟现实技术,对图形生成加速技术做了具体分析,并在真实数据三维地形的特点下,对规则格网地形分辨率可视化算法建立,并做好不规则三角网模型层次结构的建立,将动态实时显示全面显示。     

一种大规模地形简化的算法

在地形可视化领域,实时绘制复杂地形场景的最有效工具是LOD技术。结合四叉树数据结构与不规则三角网数据结构的优点,提出一种混合数据结构的地形简化算法。算法通过使用不同的误差阈值,实现了视点相关的地形简化。同时通过有效的误差控制原则,解决了不规则三角网分块之间的拼接问题,消除了地形裂缝。实验结果证明了算法能高效地生成地形的连续多分辨率模型,实现地形场景的平滑绘制。     

基于FBM分形特征的快速小波地形模拟算法

该文基于FBM分形原理,采用Haar小波对自然地形数据进行模拟构建。在分析自然地形分形系数与小波系数之间关系的基础上,建立基于Haar小波的地形构建模型;通过对真实地形数据不同阶层小波系数统计计算得到分形特征参数;以构建模型为基础,结合分形特征参数,模拟生成自然地形。该算法相对真实地形数据具有小的交叉熵,且计算复杂度较小,仿真数据验证了算法的有效性。     

Evaluation of terrain models for the geocoding and terraincorrection, of synthetic aperture radar (SAR) images

The variability of the resolutions and the presence of artifacts cause inaccurate correction of the terrain-induced geometric distortions in synthetic-aperture radar (SAR) images. To quantify the effects of these inaccuracies on SAR terrain correction, corrections of a Seasat SAR image were performed using a 1° US Geological Survey (USGS) terrain model, a 7.5-min USGS terrain model, and a terrain model derived from stereoimagery acquired from SPOT. Geometric verifications of the corrected imagery showed that the resolution of the 1° terrain model is not adequate to resolve many features in the Seasat image. Geometric verifications of images corrected with the two higher resolution terrain models showed localized errors as large as 52 m for mountain peaks. However, comparison of data corrected with those models shows that both produce results that differ by less than the resolution of either of them. Periodic artifacts observed in the terrain models translated to ground range differences of 18 m, which are well below the resolution of the SAR imagery     

An automated approach for implementing GTD to model 2-D terraineffects at microwave frequencies

The impetus for the work described arose out of the need to model absolute signal strength for a microwave landing system (MLS) operating in the presence of irregular terrain. A complete, automated approach for predicting absolute signal strength at microwave frequencies for sites involving irregular, 2-D terrain profiles is presented. The approach involves two computer models: one to convert raw terrain elevation data into a linear profile; the other to estimate path loss using the geometrical theory of diffraction. The linearization of a terrain profile is accomplished by mapping raw terrain data into a phase domain and then identifying significant terrain features from the stationary phase points as defined by Fermat's principle. Since the entire modeling process is automated, little expertise on the part of the user is required. Validation of the approach is given by comparisons of measured and modeled signal strength data for representative sites. While the model described is limited to 2-D terrain, the approach is applicable to 3-D terrain as well     

一个地形可视化系统的建立与阴影分析计算

地形可视化对土地的规划利用和综合决策都具有重要的应用价值。它能够给人们提供一个直观的地理形象，便于实施操作和想定作战方案，从而取代传统的沙盘模型且易于进行地形定量计算。本文根据某工程的实际需要建立了一个地形可视化系统，并对太阳时角地形造影(阴影)进行了分析计算。实用结果证明：该系统效果良好。     

SEKE: A computer model for low altitude radar propagation over irregular terrain

SEKE, a new site-specific propagation model for general terrain, makes use of the original Lincoln Laboratory models geometrical optics (GOPT), low altitude propagation spherical earth (LAPSE), and low altitude propagation knife edges (LAPKE) to compute multipath, spherical earth diffraction, and multiple knife-edge diffraction losses. The proper algorithm is selected based on terrain geometry, antenna and target heights, and frequency. Comparison of model predictions with measurements over several paths ranging from level to rough at five frequencies (X-band through VHF) is presented. A brief discussion on the performance of SEKE over general terrain with respect to the expected performance of the two other general terrain-specific models (Longley-Rice and terrain integrated rough earth model (TIREM)) is given.     

相干雷达高度表大地回波去相关研究与实验

由于非刚体目标自身的变化或者刚体目标与雷达之间的距离、视角发生变化都会产生大地回波去相关现象.文中针对上述现象建立了大地回波的几何与幅度起伏模型,对机载相干雷达高度表回波特性进行了仿真研究.文中还利用S波段相干脉冲散射计开展了大地回波测量实验,对回波数据进行了相干处理,并对仿真结果进行了实验验证.仿真与实验的结果表明:大地回波的去相关损失取决于地面粗糙度以及载机在一个脉冲重复周期内移动的距离.     

VHF propagation over hilly, forested terrain

Propagation measurements at low altitudes over hilly, forested terrain made with the objective of developing a computer-based propagation model capable of predicting path loss over similar terrain given the terrain profile between transmitter and receiver are reported. The measurements were made at a frequency of 110.6 MHz with the very high frequency omnidirectional range (VOR) station at Gardner, MA, as a transmitter. The received signals were measured at distances between 7 and 15 km by making vertical descents with a helicopter from altitudes of roughly 600 m down to 10 m above ground. Negligible specular ground reflection was observed from this terrain, and no reflection is included in the model. We found good agreement between the measurements and a multiple-diffraction model based on an extension of the Deygout approximation. Use of two knife edges was sufficient to characterize the terrain diffraction. Predictions of the Longley-Rice computer model are included for comparison.     

基于空间自相关的地形建模简化研究

针对基于数字高程模型（Digital Elevation Model,DEM）数据的大规模三维地形简化问题,提出了基于空间自相关理论的地形建模简化方法。该方法考虑地形坡度这一表达地形特征关键因素,以地貌特征区域相似与高程数据相关性为依据,对地形数据进行聚类分析,获取区分地形的特征值,在此基础上采用基于倾斜度的距离加权法计算中心点的高程值,生成新的网格进行地形构建。实验结果表明,该方法一定程度上降低了数据规模,减少了相对误差,同时较好的保持了地形特征。