面向大尺度战场的地貌晕渲增强方法

地貌晕渲是大尺度战场仿真中的重要一环,针对现有的地貌晕渲技术在细节处纹理特征不明显的问题,提出了一种结合高程曲率和环境光遮蔽的大尺度战场地貌晕渲增强方法.第1步,通过分析数字高程数据的曲率属性生成地形曲率图,曲率图与卫星影像叠加可以突出显示地貌特征线.第2步,提出一种基于深度可分离卷积的环境光遮蔽计算方法,能够增强战场地形在沟壑处的视觉表现.最后将曲率图、环境光遮蔽与卫星影像三者融合生成实时地貌晕渲效果.实验表明,本文方法可以在较低级别的全球卫星影像上呈现更好的视觉效果,使得观察者在把握三维地形整体走势的同时,能进一步分析地貌细节处的纹理特征.     

面向遥感叶面积指数产品的地形校正研究

地形校正是提高复杂地形区地表参数遥感定量化反演精度的重要手段。当前广泛应用的遥感叶面积指数产品（Leaf Area Index, LAI）多具有一定的地形误差,减少地形影响、提升其产品精度有着非常重要的意义。以我国江西省千烟洲地区为研究区域,利用地面实测LAI数据、LandsatTM数据和高程数据等,基于高程标准差和GLOBMAP LAI产品值的关系,建立面向叶面积指数产品的地形校正模型,利用这一模型对GLOBMAP LAI产品进行地形校正。结果表明：校正后的LAI与地面实测数据更为接近,LAI产品与地面测量值的RMSE由2.11下降到2.04;校正后LAI产品的标准差由2.08下降至1.69,LAI产品的地形误差得到了较好的改正。该方法较好地完成了LAI产品的地形校正,进一步提高了产品精度,具有一定的实用价值。     

一种新的三维地景库的建模方法

针对传统的模拟器计算机成像系统之不足,提出了1种新的视景系统的建模方法,即基于矢量数字地图的三维地景生成算法。该算法以矢量地图为约束,各种地表纹理作为输入样图,用矢量地图中的高程信息构建三维地形网格,并根据矢量数字地图中图元之间的不同属性映射相应的纹理,得到了与矢量数字地图相一致的三维地景。与传统的地景库生成算法相比,新算法生成的三维地景更加真实精确;解决了以往地景库一经生成就无法更改的问题;具有一定的预测和重现场景的功能;缩短了地景库的开发周期,降低了开发成本。同时,运用了基于视点的地景数据动态调度策略,可实现真实场景的实时绘制。     

三维地形生成及其可视化处理研究

针对在三维地形处理领域中存在的地形数据获取困难,可视化处理过程复杂真实感效果不强的问题.文中提出了一种三维地形生成和可视化处理的方法,该方法采用分形算法生成虚拟地形数据,然后将其存储为地理信息系统中通用的数字高程数据格式,最后将数据导入三维建模软件Multigen Creator 3.0中,结合网格生成、三维投影和纹理映射等,进行可视化处理.仿真试验表明:该方法能快速获取有效的地形高程数据,经过处理后得到了直观的,真实感较强的三维显示效果图.该文为三维地形生成和可视化处理问题提供了一种有效的、可实现的处理方法.     

基于改进蚁群算法的直升机航迹规划仿真

提出了基于改进蚁群算法的直升机航迹规划仿真过程,直升机在执行任务的过程中,有效地利用地形以躲避雷达扫描是直升机提高其生存能力的关键手段。利用真实地形的DEM数字高程建立真实地形;根据目标与雷达的交会几何关系,推算出雷达在真实地形中扫描的盲区;并针对传统的蚁群算法缺点,提出一种改进的蚁群算法仿真飞机飞行通过雷达区域,为其选择一条安全的飞行路线,使直升机从起始点到目的点的路径最优,从而达到提高战斗效率的目的。     

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.     

基于优化的电势理论规划三维飞行路径

利用优化的电势理论进行飞行器三维航迹规划。对电势理论进行了优化,使其既能回避雷达、火力威胁,又能有效地回避地形威胁,使规划出的三维航迹具有一定的实用性。根据突防任务的需要,确定地形威胁与雷达、火力威胁的权重,并将模拟地形的高程数据与雷达、火力威胁按各自的权重叠加得到综合威胁电场;通过限定位于起始点和目标点之间的搜索范围,并对搜索条件进行改进,保证飞行路径最终能收敛于目标点;最后,用坡度限制平滑算法、曲率限制平滑算法对航迹进行法向加速度和曲率限制使其符合飞行器机动性能和可飞性要求。仿真结果表明,优化的电势理论可以进一步考虑地形威胁,而且在能够考虑目标点附近的各种威胁,提高了该方法的实用性,还能缩短航线规划的时间。     

大面积人工数字地图生成软件的设计与实现

为给地形匹配研究提供低成本、大面积、生成速度快的随机数字地图,开发了一种数字地图生成软件.选用二维离散AR算法产生模拟数字地形,采用小块地图拼接的方法生成大面积地图.用标准C语言编程实现地形数据的快速生成和调用,并根据要求可以任意加入威胁地形.建立了便于调用数据的地形数据存储格式.利用该软件生成大面积数字地图速度快,面积可以按需要设定,生成的地形符合实际地形特征.由于每次生成的地形特征可以不相同,所以该软件可为地形匹配研究提供有效的大面积地形数据.     

Cross-validation as a means of investigating DEM interpolation error

Studies of the detailed characteristics of DEM error have been hampered by the difficulty in obtaining a large sample of error values for a DEM. The approach proposed in this paper is to resample a DEM to a lower resolution and then reinterpolate back to the original resolution which produces a large sample of error values well distributed across the DEM. This method is applied to a sample area from Scotland, which contains a variety of terrain types. The results show that the standard measure of error, the root mean square error (RMSE) of elevation, shows only moderate correlation with a visual assessment of the quality of DEMs produced by a range of interpolation methods. The frequency distribution and strength of spatial autocorrelation are shown to vary with the initial data density and interpolation method. When the source data density is low, the error has strong spatial autocorrelation and a distribution that is close to being Gaussian. However, as the data density increases, levels of spatial autocorrelation drop and the distribution becomes leptokurtic with values very strongly clustered around zero. At the level of the individual DEM point, elevation error is shown to be a poor predictor of error in slope derivatives which depend on the spatial pattern of elevation errors around the point and are also sensitive to differences in terrain. At the level of a whole DEM, however, RMSE of elevation is a good predictor of RMSE in gradient and aspect but not of curvature.     

基于RS和GIS的洪涝灾害监测与评估研究

以鄱阳湖区为例,对洪灾的快速监测与评估进行研究。首先探讨了洪灾监测与评估所需的基础背景数据,包括数字地面高程模型(DEM)、本底水体数据及土地利用数据;然后介绍了以RS和GIS为支撑,对洪涝灾害进行监测评估,实现了对遥感获取的灾情信息与地面实况信息进行各种空间分析与专题分析,从而提取出洪涝淹没的范围和面积,及时地反映出淹没的程度及地理位置,快速地对洪涝灾情进行评估。最后结果显示:该方法快速、有效,能够为相关决策部门了解灾情、制定救灾方案以及灾后规划等提供决策支持。     

基于静态LOD的输电线路虚拟地形渲染优化算法

针对输电线路三维可视化系统中大规模地形场景的渲染问题,提出一种基于静态LOD的虚拟地形绘制优化算法. 建立输电线路廊道内地形高程数据的分块模型,将视角移动速度纳入细节层级的评价因子中,结合视点距离、地形复杂度等因素改进评价函数. 通过阈值判断网格内数据点高程值的方差,选择不同的线性插值函数完成地形曲面的模拟效果. 实验结果表明所提算法有效减少了运动状态下地形三角面的绘制数,具有更加流畅的虚拟场景帧数和良好的地形仿真效果.     

TOPO III: a FORTRAN program for terrain analysis

TOPO III is a FORTRAN program that operates with rectangular arrays of equally spaced elevations, producing lists of terrain parameters (coordinates, elevation, average and maximum relief, average and maximum slope, azimuth of maximum slope, and topographic shape: slope, ridge, valley, knob, sink, saddle), point-frequency distributions of maximum and average slope, symbolic slope maps, frequency distributions of areas comprising contiguous points with the same topographic shape, and topographic shape maps with point-frequency distributions of shape types. The program compares a central elevation with interpolated elevations around the perimeter of a circular “window”, and the radius of the window may be increased in successive passes through the array. The results have been used for slope studies, for analysis of terrain factors in environmental studies, and for terrain classification.     

Urban flood risk analysis for determining optimal flood protection levels based on digital terrain model and flood spreading model

The objective of the paper is to present a new risk-analysis approach for the assessment of optimal flood protection levels in urban flood risk management, which is based on an active contour method. Although the active contour method is a very popular research topic, there has been no attempt made on deriving a model for simulating flooding and inundating to date, as far as we are aware. We have developed a flooding prototype system, which consists of two main parts: a digital terrain model and a flood simulation model. The digital terrain model is constructed using real world measurement data of GIS, in terms of digital elevation data and satellite image data. A pyramidal data arrangement structure is used for dealing with the requirements of terrain details with different resolutions. A new flooding model has been developed, which is useful for urban flood simulation. It consists of a flooding image spatial segmentation based on an active contour model, a water level calculation process, a standard gradient descent method for energy minimisation. When testing the 3D flood simulation system, the simulation results are very close to the real flood situation, and this method has faster speed and greater accuracy of simulating the inundation area in comparison to the conventional 2D flood simulation models.     

DEM建模中基于等高线的高程样本值预处理方法

根据DEM的精度在很大程度上取决于高程样本点精度这一特性,提出了一种高程样本值的线性预处理方法。该方法将两根相邻等高线间的地形近似视为直线变化,根据这个假设应用简单的三角计算,可以计算出相邻等高线上线性变化方向上的两点连线上任意一点的高程值,即增加高程样本值的数量,又增加了样本值的精度,从而达到了提高最终DEM的精度的目标。     

基于高程归一化的布料模拟滤波算法

点云的滤波处理是LiDAR数据处理中一个非常重要的环节,即分离出点云数据中的地面点和非地面点,为后续的数据处理打下基础。本文在传统的渐进式数学形态学滤波和布料模拟滤波方法的基础上,考虑到渐进形态学滤波对于地面点分离的效果尚可,也就是能基本保留所有的地面点,但由于其地形的自适应性较弱,高差阈值随着地形坡度的变化也有着不稳定性使得一部分非地面点容易被当成地面点,而布料模拟滤波算法具备运行效率高的优点,且布料模拟滤波在地形平坦地区的滤波效果较地形起伏大的地区滤波效果更好。因此在渐进形态学滤波结果的基础上建立目标区域的粗DEM栅格数据,然后对目标区域点云数据中各点的高程值进行一个归一化处理,消除目标区域中地形有起伏的因素给布料模拟滤波结果带来的影响。最后采用ISPRS官方网站的3组标准数据样本的实验结果表明,相比于传统的渐进式形态学滤波的结果其I类误差降低,相比于未进行归一化过程的布料模拟滤波算法的结果其II类误差降低,而其总误差均降低,达到较好的滤波效果。     

A comparison of Landsat TM and MODIS vegetation indices for estimating forage phenology in desert bighorn sheep (Ovis canadensis nelsoni) habitat in the Sonoran Desert,USA

Sonoran Desert bighorn sheep (Ovis canadensis mexicana) occupy rugged upland areas that experience irregular periods of vegetation growth associated with precipitation events. These episodic and often spatially limited events provide important forage and preformed water resources that may be important drivers of animal movement and habitat use. Habitat-use models that incorporate forage phenology would broaden our understanding of desert bighorn ecology and have considerable potential to inform conservation efforts for the species. Field-based methods are of limited utility to characterize vegetation phenology across large areas. Vegetation indices (VI) derived from satellite imagery are a viable alternative, but may be confounded by areas of high relief and shadow effects that can degrade VI values. The varying spatial and temporal resolutions of readily available satellite sensors, such as the Landsat thematic mapper (TM) and moderate-resolution imaging spectrometer (MODIS), present additional challenges. In this study, we sought to minimize degrading effects of terrain on TM- and MODIS-based estimates of vegetation phenology. We compared effects of high topographic relief on time series MODIS- and TM-based VI such as the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) using VI departures from average (DA) in shaded and unshaded areas. Sun elevation angle negatively impacted TM-derived NDVI and EVI values in areas of steep terrain. In contrast, MODIS-derived NDVI values were insensitive to sun elevation and terrain effects, whereas MODIS-derived EVI was degraded in areas of steep terrain. Time series MODIS NDVI and EVI DA values differed significantly during months of low sun elevation angle. Average MODIS EVI departure values were ≥20% lower than NDVI under these conditions, confounding time series estimates of plant phenology. Our best results were obtained from MODIS 16-day composited NDVI. These remote-sensing-based VI estimates of seasonal plant phenology and productivity can be used to inform models of habitat use and movements of desert bighorn over large areas.     

基于迁移学习的低空摄影测量滑坡方量估算方法

针对现有方法难以准确地估算山体滑坡体积的问题,引入人工智能算法,提出耦合迁移学习与微分算法的低空摄影测量山体滑坡方量估算方法。首先,利用SfM与SGM密集匹配等算法从低空无人机立体影像中解算出高精度三维密集点云,结合可见光植被指数和双边滤波算法从密集点云中剥离出目标区地面点云;然后,构建深度神经网络插值模型来表征二维坐标与高程之间的非线性映射关系,并基于参数共享的迁移学习来自适应优化深度神经网络以实现滑坡目标区高程值预测,进而重构滑坡区域的数字地表模型;最后,基于目标区滑坡前后数字地表模型高程差值和微分算法实现山体滑坡方量估算。实验结果表明,该方法平均相对误差为2.7%,相比常用的方法,显著提高了滑坡方量估计精度,并能适应不同地形条件下滑坡方量估算。     

基于增强型MAD算法的地形辅助导航仿真研究

针对地形辅助导航系统中的地形匹配计算问题,提出一种增强型平均绝对差(MAD)算汉.算法采用最近时刻的位置偏差信息计算当前搜索区域中的高程匹配序列,使系统在任意时刻均可获得当前的地形匹配值,保证了匹配计算的连续性.在此基础上,根据MAD相关系数对数字地图上各搜索点的位置信息进行融合计算,以获取最佳的匹配点.为降低计算冗余量,在重叠的搜索区域对算法进行了优化.另外,当地形特征不明显时引入了判决机制,以增强算法的稳定性.仿真结果表明算法具有较好的动态定位效果.     

茂密植被区域LiDAR点云数据滤波方法研究

点云数据的滤波和分类是激光雷达数据应用处理重要环节,是当前研究的热点问题。本文针对茂密植被区域点云数据的特点,提出了以移动窗口和坡度算法为基础的改进的点云数据滤波算法。试验结果表明,改进的滤波算法对地形变化复杂、植被郁闭度较高覆盖、地面激光脚点比少的点云数据有良好的效果。     

Vegetation-Limited Ground-to-Air Surveillance

It is possible to estimate the limitations on ground-to-air visibility around a point using digital terrain models in which terrain height is given on a rectangular grid and the vegetation class within defined areas is specified. The screening effect of the vegetation can be estimated better by using the inherent autocorrelation in elevation angle data given as a function of azimuth angle about a fixed point. This type of model is useful when the proposed number of observation sites is too large to warrant surveying them, or the precise actual locations cannot be ascertained in advance of the requirement, as is often the case in simulation studies involving mobile observers. The distribution of elevation angle may be non-normal. A procedure is described here to facilitate the use of autoregressive equations which require normally distributed variables.