Underwater Digital Terrain Model with GPS-aided High-resolution Profile-scan Sonar Images

The whole procedures of underwater digital terrain model (DTM) were presented by building with the global positioning system (GPS) aided high-resolution profile-scan sonar images.The algorithm regards the digital image scanned in a cycle as the raw data.First the label rings are detected with the improved Hough transform (HT) method and followed by curve-fitting for accurate location;then the most probable window for each ping is detected with weighted neighborhood gray-level co-occurrence matrix;and finally the DTM is built by integrating the GPS data with sonar data for 3D visualization.The case of an underwater trench for immersed tube road tunnel is illustrated.

基于Terrain model的三角化运算法则

针对目前出现的大量的物体表面扫描数据的分割与插值方法,本文提出了一个新的适合Terrain model及其相近的三角化运算法则,并给出了部分运算程序代码。该运算法则经检验与运用,具有很好的实用性。

Three-Dimensional TIN Algorithm for Digital Terrain Modeling

The problem of taking an unorganized point cloud in 3D space and fitting a polyhedral surface to those points is both important and difficult. Aiming at increasing applications of full three dimensional digital terrain surface modeling, a new algorithm for the automatic generation of three dimensional triangulated irregular network from a point cloud is pro- posed. Based on the local topological consistency test, a combined algorithm of constrained 3D Delaunay triangulation and region-growing is extended to ensure topologically correct reconstruction. This paper also introduced an efficient neighbor- ing triangle location method by making full use of the surface normal information. Experimental results prove that this algo- rithm can efficiently obtain the most reasonable reconstructed mesh surface with arbitrary topology, wherein the automati- cally reconstructed surface has only small topological difference from the true surface. This algorithm has potential applica- tions to virtual environments, computer vision, and so on.

Use of the Wavelet Transform for Digital Terrain Model Edge Detection (Special Issue—Wavelet Analysis)

The purpose of this work is to analyze the feasibility of using the wavelet transform in the edge detection of digital terrain models (DTM) obtained by Laser Scanner. The Haar wavelet transform and the edge detection method called Wavelet Transform Modulus Maxima (WTMM), both implemented in Matlab language, were used. In order to validate and verify the efficiency of WTMM, the edge detection of the same DTM was performed by the Roberts, Sobel-Feldman and Canny methods, chosen due to the wide use in the scientific community in the area of Image Processing and Remote Sensing. The comparison of the results showed superior performance of WTMM in terms of processing time.

RANDOM TERRAIN MODEL

In order to slove a realistic test problem of TF/TA algorithm, it is necessary to make a discrete terrain model. The model has adjustable roughness parameters so as to test the optimization procedure for different types of terrain. In this paper, an algorithm to generate random terrain data is given.

An Efficient Representation of Quadtrees and Bintrees for Multiresolution Terrain Models

A space-filling curve in 2,3,or higher dimensions can be thought as a path of a continuously moving point.As its main goal is to preserve spatial proximity,this type of curves has been widely used in the design and implementation of spatial data structures and nearest neighbor-finding techniques.This paper is essentially focused on the efficient representation of Digital Ele-vation Models(DEM) that entirely fit into the main memory.We propose a new hierarchical quadtree-like data structure to be built over domains of unrestricted size,and a representation of a quadtree and a binary triangles tree by means of the Hilbert and the Sierpinski space-filling curves,respectively,taking into account the hierarchical nature and the clustering properties of this kind of curves.Some triangulation schemes are described for the space-filling-curves-based approaches to efficiently visualize multiresolu-tion surfaces.

Multi-resolution representation of digital terrain models with terrain features preservation

multi-resolution TIN model is an important issue in the contexts of visu-alization,virtual reality (VR),and geographic information systems (GIS). This paper proposes a new method for constructing multi-resolution TIN models with multi-scale topographic features preservation. The proposed method is driven by a half-edge collapse operation in a greedy framework and employs a new quadric error metric to efficiently measure geometric errors. We define topographic features in a multi-scale manner using a center-surround operator on Gaussian-weighted mean curvatures. Experimental results demonstrate that the proposed method performs better than previous methods in terms of topographic features preservation,and is able to achieve multi-resolution TIN models with a higher accuracy.

Dynamic Analysis of the Seafloor Pilot Miner Based on Single-Body Vehicle Model and Discretized Track-Terrain Interaction Model

In order to achieve the complex dynamic analysis of the self-propelled seafloor pilot miner moving on the seafloor of extremely cohesive soft soil and further to make it possible to integrate the miner system with some subsystems to form the complete integrated deep ocean mining pilot system and perform dynamic analysis, a new method for the dynamic modeling and analysis of the miner is proposed and developed in this paper, resulting in a simplified 3D single-body vehicle model with three translational and three rotational degrees of freedom, while the track-terrain interaction model is built by partitioning the track-terrain interface into discrete elements with parameterized force dements built on the theory of terramechanics acting on each discrete dement. To evaluate and verify the correctness and effectiveness of this new modeling and analysis method, typical comparative studies with regard to computational efficiency and solution accuracy are carried out between the traditional modeling method of building the tracked vehicle as a multi-body model and the new modeling method. In full consideration of the particMar structure design of the pilot miner, the special characteristics of the seafioor soil and the hydrodynamic force of near-seafloor currnt, the dynamic simulation analysis of the miner is performed and discussed, which can provide useful guidance and reference for the practical miner system in design and operation. This new method can not only realize the rapid dynamic simulation analysis of the miner but also make possible the integration and rapid dynamic analysis of the complete integrated deep ocean mining pilot system in further researches.

Distributed modeling of direct solar radiation on rugged terrain of the Yellow River Basin

Due to the influences of local topographical factors and terrain inter-shielding, calculation of direct solar radiation （DSR） quantity of rugged terrain is very complex. Based on digital elevation model （DEM） data and meteorological observations, a distributed model for calculating DSR over rugged terrain is developed. This model gives an all-sided consideration on factors influencing th a resolution of 1 km × 1 km for thDSR. Using the developed model, normals of annual DSR quantity wie Yellow River Basin was generated, with DEM data as the general characterization of terrain. Characteristics of DSR quantity influenced by geographic and topographic factors over rugged terrain were analyzed thoroughly. Results suggest that： influenced by local topographic factors, i.e. azimuth, slope and so on, and annual DSR quantity over mountainous area has a clear spatial difference; annual DSR quantity of sunny slope （or southern slope） of mountains is obviously larger than that of shady slope （or northern slope）. The calculated DSR quantity of the Yellow River Basin is provided in the same way as other kinds of spatial information and can be employed as basic geographic data for relevant studies as well.

VALIDATION OF NEAR-SURFACE WINDS OBTAINED BY A HYBRID WRF/CALMET MODELING SYSTEM OVER A COASTAL ISLAND WITH COMPLEX TERRAIN

The results from a hybrid approach that combines a mesoscale meteorological model with a diagnostic model to produce high-resolution wind fields in complex coastal topography are evaluated.The diagnostic wind model(California Meteorological Model,CALMET) with 100-m horizontal spacing was driven with outputs from the Weather Research and Forecasting(WRF) model to obtain near-surface winds for the 1-year period from 12 September 2003 to 11 September 2004.Results were compared with wind observations at four sites.Traditional statistical scores,including correlation coefficients,standard deviations(SDs) and mean absolute errors(MAEs),indicate that the wind estimates from the WRF/CALMET modeling system are produced reasonably well.The correlation coefficients are relatively large,ranging from 0.5 to 0.7 for the zonal wind component and from 0.75 to 0.85 for the meridional wind component.MAEs for wind speed range from 1.5 to 2.0 m s-1 at 10 meters above ground level(AGL) and from 2.0 to 2.5 m s-1 at 60 m AGL.MAEs for wind direction range from 30 to 40 degrees at both levels.A spectral decomposition of the time series of wind speed shows positive impacts of CALMET in improving the mesoscale winds.Moreover,combining the CALMET model with WRF significantly improves the spatial variability of the simulated wind fields.It can be concluded that the WRF/CALMET modeling system is capable of providing a detailed near-surface wind field,but the physics in the diagnostic CALMET model needs to be further improved.

Terrain Simplification Research in Augmented Scene Modeling

Augmented reality is the merging of synthetic sensory information into a user's perception of a real environment. As one of the most important tasks in augmented scene modeling, terrain simplification research has gained more and more attention. In this paper, we mainly focus on point selection problem in terrain simplification using triangulated irregular network. Based on the analysis and comparison of traditional importance measures for each input point, we put forward a new importance measure based on local entropy. The results demonstrate that the local entropy criterion has a better performance than any traditional methods. In addition, it can effectively conquer the 'short-sight' problem associated with the traditional methods.

Modeling the 3D Terrain Effect on MT by the Boundary Element Method

A numerical method is put forward in this paper, using the boundary element method （BEM） to model 3D terrain effects on magnetotelluric （MT） surveys, Using vector integral theory and electromagnetic field boundary conditions, the boundary problem of two electromagnetic fields in the upper half space （air） and lower half space （earth medium） was transformed into two vector integral equations just related to the topography ： one magnetic equation for computing the magnetic field and the other electrical equation for computing the electrical field. The topography integral is decomposed into a series of integrals in a triangle element. For the integral in a triangle element, we suppose that the electromagnetic field in it is the stack of the electromagnetic field in the homogeneous earth and the topography response which is a constant; so the computation becomes simple, convenient and highly accurate. By decomposition and computation, each vector integral equation can be calculated by solving three linear equations that are related to the three Cartesian directions. The matrix of these linear equations is diagonally dominant and can be solved using the Symmetric Successive Over-Relaxation （SSOR） method. The apparent resistivity curve of MT on two 3D terrains calculated by BEM is shown in this paper.

地形影响的水平相关模型在CMA-MESO中的应用

在背景误差水平相关模型中引入地形作用,研究复杂地形下近地面观测资料同化对分析和预报的影响。CMAMESO三维变分系统中背景误差水平相关关系采用高斯相关模型描述,观测信息在高度追随坐标的模式面上各向同性传播。然而在地形复杂的近地面层,观测信息传播受到山脉阻挡,因而其背景误差协方差非均匀且各向异性,观测信息传播应随地形高度变化。为此,采用美国国家气象中心NMC方法统计复杂地形下背景误差水平相关结构,构建包含地形高度和地形梯度影响的高斯相关模型,并将改进的水平相关模型应用于CMA-MESO三维变分分析。理想试验表明:考虑地形项的水平相关模型方案使观测信息以随地形高度变化的各向异性形式传播,越过大地形观测信息影响明显减弱,分析增量更加合理。我国北方一次强降水过程分析预报试验表明:随地形高度变化的水平相关模型方案使地面观测信息各向异性传播,削弱了大地形处近地面的分析增量,对降水预报略有正贡献。针对华东地区降水过程进行5 d逐小时快速更新分析预报循环试验结果表明,随地形变化的水平相关模型方案对10 m风场和24 h时效内降水预报有正贡献。

基于机载多角度InSAR技术的复杂地形高精度DEM重建方法

干涉合成孔径雷达(Interferomtric Synthetic Aperture Radar,InSAR)是全天时、全天候获取三维地表信息重要的技术手段。机载InSAR系统具有机动灵活、多角度获取数据的优势,可以高效率、高精度获取数字高程模型(Digital Elevation Model,DEM)数据。但是,在地形复杂区域,InSAR侧视成像易在地形陡峭区域形成较大范围的阴影和严重的叠掩现象,阴影和叠掩区域在SAR图像上体现为信息的丢失,从而导致DEM数据大面积无效数据的存在,严重影响DEM数据的质量及应用。针对这一问题,本文提出了基于机载多角度InSAR技术的复杂地形高精度DEM重建方法,基于考虑地形起伏的机载多角度InSAR数据获取任务规划设计,最大程度的避免阴影和叠掩导致的无效数据;基于高精度InSAR数据处理,保证每个角度DEM数据精度的高度一致性;基于快速多角度DSM数据融合与滤波处理,实现多角度InSAR体制复杂地形DEM高精度重建。本文以四川省西部山区大坡度、非连续等复杂地形为例,基于本文提出的方法,利用3个角度InSAR数据融合处理,生成了高精度DEM数据,试验结果表明,本文提出的方法获取复杂地形DEM数据高程均方根误差为0.6 m,同时,数据有效率大于99%。

滚动球变换支持下的TIN-DDM地形特征线自动提取方法

针对传统规则格网数字高程模型地形特征线提取方法中存在阈值难以定量调控、连接方式无法自适应调整以及地形特征线类型不完整的问题,将滚动球变换模型应用于不规则三角网数字水深模型(triangulated irregular network digital depth model,TIN-DDM)地形特征线的自动提取,在构建临界滚动球半径关联的地形特征点定量识别判定准则基础上,引入地形形态边界点概念,采用逆向工程的建模思路,建立了以剖分单元为基础的地形特征线自动提取模型,结合地形类型判定准则的多尺度表达特性及顾及水深数值的地形特征优化模型,提出了可多尺度表达且类型完整的地形特征线自动提取方法。试验结果表明:相比于经典地表流水模拟方法,该方法可实现完整、连续且细分的TIN-DDM地形特征线自动提取及多尺度表达,且提取的地形特征线具有更高的地形重构精度。

基于约束DT的大规模动态地形的构建

大规模地形场景模型复杂、数据量大,动态实时构建效率低。论文研究了大规模地形的动态构建问题,提出了一种基于约束DT进行地形动态实时构网的方法。该方法将大规模的地形分割成若干小的地形块,将地形块的四个顶点添加到地形数据集中,对每个地形块单独构网,从而实现大规模地形三角网的快速构建。针对地形的动态变化,采用添加扩展约束的方式仅对扩展约束内部动态变化的地形进行重新构网,提高了地形三角网动态更新的效率。在进行地形纹理贴图时,对地形块进行分块处理,建立纹理数据与地形子块内三角网的映射关系实现纹理贴图,提高了渲染效率。实验结果表明,地形分块动态建模提高了地形动态变化后构网和绘制的效率。

高原地区VHF地空通信覆盖范围影响因素研究

针对利用地形遮蔽法计算的民航VHF通信信号覆盖范围较粗略的问题,提出了一种在原有的算法下加入雾衰减从而提高信号覆盖精度的算法模型,并构建可视化的显示平台。首先,以西藏某高原地区VHF通信监视台站为例,利用地理信息系统从实际的地图中获取台站周围的数字高程模型(DEM),计算在地形影响下不同高度层上的信号传播截止距离;其次,根据国际电联无线电通信部门(ITU-R)P系列建议书中的雾衰减模型,构造在地形和雾共同影响下的新算法模型;最后,给定飞行高度、发射频率、发射功率等进行仿真。结果表明,多因素影响下的信号覆盖范围比单因素下的覆盖范围精确,可以为VHF地面通信监视台站选址、飞行航线规划以及西部地区民航发展提供有效支撑。

典型峡谷Ⅴ型地貌下桥址区风特性

为得到山区峡谷典型Ⅴ型地形下的桥梁抗风设计的关键风特性参数,通过“数值风洞试验”建立模型,以实桥为工程背景构建三维地形网格,基于3种典型湍流模型和流体壁面粗糙度对桥位的风场特性进行分析,选取最优湍流模型和流体壁面粗糙度对该地形桥位处的风场特性进行分析;围绕两个影响桥址区风特性的地形参数(山体高度和夹角),阐明Ⅴ型峡谷地形下风特性参数的变化规律,并与现行规范进行对比,推算桥面设计基准风速。结果表明:该Ⅴ型峡谷地形的最佳湍流模型和流体壁面粗糙度分别为RNG k-ε和20 m;随着山体高度及山体夹角两参数的变化,风速增加幅度分别为2.37%~12.56%和1.24%~6.98%;山体高度及山体夹角两变参数下,梯度风高度分别为700 m和800 m左右;实际湍流强度大于规范中四类地表规范值,在离地高度40 m范围内,湍流强度更接近于D类地表。实际Ⅴ型峡谷桥址区不能简单按规范归为C类或D类地形,在设计风参数计算时应综合考虑规范和经验公式,还可借助模拟手段来提高其准确性。

电大山区地物环境中电波传播的电磁计算

在无人驾驶与无人机等新兴行业中,信号覆盖范围的要求较高,不仅仅在城市,在人迹罕至的山地、沙漠、森林中也需要无线信号的覆盖才能真正完成远程操控,这些地区更多需要考虑的是地势变化对电磁传播所带来的影响。计算电磁学中的一致性几何绕射理论方法是分析电大环境电磁问题的有效方法,使用计算电磁学的方法研究电磁波在山区地物环境中的传播规律。给出了一种建立不规则地形模型的新方法,可以通过数字高程的网格数据生成电磁算法可用的三次多项式曲面,使用多个立方曲面对不规则地形进行拼接,使用平均均方根误差验证模型数据的准确性。基于所得的地形数据,完成了并行的几何光学算法,并对区域电磁场的分布进行了仿真计算。选取了实际山区地物环境进行了实地测量,测量结果与仿真结果对比趋势一致,验证了该方法在非规则地形中电磁波传播分析中的有效性。考虑环境电磁计算的规模,建立了相应的并行策略,100核测试的并行效率可以保持在80%以上。

复杂地形对风速廓线的影响

随着风电利用的发展,越来越多的风电场建立在复杂地形的山区,为了更好地进行风能评估和风电预报,就需要了解复杂地形对风速廓线的影响。本文基于薄翼理论和湍流边界层扰动的线性化理论,采用两层模型对坡度较小的山地在其二维横截面上的风廓线进行了预测,该模型能够较为准确地预报地形、压力、稳定度对风速增速的影响,但对于三维地形或其他因素产生的风速的复杂变化,需要进一步将其扩展至三维,并结合数值模拟进行研究。