机载LiDAR点云的Delaunay三角网快速生成算法     

罗胜  王鑫  孙玉平 《海洋测绘》2014,(2):18-20

为了提高机载激光点云的Delaunay三角网生成效率及稳定性,基于分块算法的思想,改进了点云数据的分块方式,利用点云的凸包及重心点进行数据分块,并结合子块中激光点个数阈值进行三角形子块的细分,从而避免了传统子块合并过程中复杂的相邻三角形搜索及优化处理,仅需简单的一步优化即可完成相邻子块的合并,大大提高了算法的效率。经实验证明,该算法简单、高效且稳定性好,尤其对于大数据量的机载LiDAR点云Delaunay三角网生成具有明显的优势。  相似文献   

A visualization-oriented 3D method for efficient computation of urban solar radiation based on 3D–2D surface mapping     

Jianming Liang  Wenhang Li  Abdoul Nasser Ibrahim 《International journal of geographical information science》2014,28(4):780-798

The temporal and spatial distribution of solar energy in urban areas is highly variable because of the complex building structures present. Traditional GIS-based solar radiation models rely on two-dimensional (2D) digital elevation models to calculate insolation, without considering building facades and complicated three-dimensional (3D) shading effects. Inspired by the ‘texture baking’ technique used in computer graphics, we propose a full 3D method for computing and visualizing urban solar radiation based on image-space data representation. First, a surface mapping approach is employed to project each 3D triangular mesh onto a 2D raster surface whose cell size determines the calculation accuracy. Second, the positions and surface normal vectors of each 3D triangular mesh are rasterized onto the associated 2D raster using barycentric interpolation techniques. An efficient compute unified device architecture -accelerated shadow-casting algorithm is presented to accurately capture shading effects for large-scale 3D urban models. Solar radiation is calculated for each raster cell based on the input raster layers containing such information as slope, aspect, and shadow masks. Finally, a resulting insolation raster layer is produced for each triangular mesh and is represented as an RGB texture map using a color ramp. Because a virtual city can be composed of tens of thousands of triangular meshes and texture maps, a texture atlas technique is presented to merge thousands of small images into a single large image to batch draw calls and thereby efficiently render a large number of textured meshes on the graphics processing unit.  相似文献   

三角平面拟合法在重力地形改正中的应用     

赵军  关云鹏  张海龙 《物探与化探》2012,(2):234-236,241

介绍了三角平面拟合法在重力勘查近中区地形改正中的应用。该方法应用三角平面拟合通过地形图DEM模型数据（或散点模型数据）直接内插求得地形改正量板模型的结点高程数据,实现了地形改正的电脑化作业。  相似文献   

柴达木盆地南翼山油田新近系油砂山组低渗微裂缝储集层特征及成因分析   总被引：2，自引：0，他引：2       下载免费PDF全文

臧士宾  崔俊  郑永仙  许文梅  魏金星 《古地理学报》2012,14(1):133-141

通过岩心观察、薄片鉴定并借助X衍射全岩矿物分析,对柴达木盆地南翼山油田新近系油砂山组储集层特征进行分析。该区岩石中泥质含量高,岩性复杂,可划分为泥岩、碳酸盐岩、砂岩和混积岩4种类型。储集层中发育粒间孔、溶蚀孔、微孔隙和微裂缝等,形成了具有双重孔隙介质的储集空间特征。微裂缝是该区主要渗流通道,而微孔隙是主要储集空间,储集层物性总体较差。该区微裂缝类型包括构造缝、溶蚀缝和成岩缝。储集层岩石纹层发育,砂质纹层和泥灰质纹层交互出现,沉积和成岩作用过程中岩石受力不均衡、碳酸盐矿物的溶解以及泥岩收缩是形成微裂缝的主要原因。该区储集层物性受压实作用明显变差,溶蚀和胶结作用同时存在,对储集层物性影响较大。储集层岩石毛管压力曲线由近似垂直的斜线段和近似水平的曲线段两部分组成,中间存在较为明显的拐折点。斜线段反映了微裂缝特征,近似水平曲线反映了微孔隙特征。利用毛管压力曲线求取的排驱压力和平均孔喉半径无法真实地表述此类微裂缝储集层的孔隙结构特征,提出了有效孔喉半径概念,可以合理表述该区微裂缝储集层孔隙结构特征。  相似文献   

Effect of Moisture on Attraction Force in Beach Sand     

TAE-HYUNG KIM  STEIN STURE 《Marine Georesources & Geotechnology》2013,31(1-2):33-47

Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (D _r ?=?30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands.  相似文献   

缝洞型碳酸盐岩油藏自吸驱油作用及其在开发中的利用   总被引：1，自引：0，他引：1  

孙来喜  王洪辉  武楗棠 《矿物岩石》2007,27(2):108-111

缝洞型碳酸盐岩油藏的多孔基质岩块是主要的储集空间,裂缝为主要的渗流通道,储油层具有非常复杂的孔隙空间结构,影响油层的注水驱油效率,从而影响油藏的最终采收率。实验表明在不具渗透性的多孔基质岩块内,毛管自吸驱油是改善基质岩块内石油动用程度的重要作用;储层在不同含水饱和度下均存在自吸作用,毛管自吸驱油系数随自吸时间延长而提高,最高可达35%;周期注水是利用毛管自吸驱油改善开发效果的有效开发方式,实验中最佳压力变化幅度为1.5倍～2倍,且投注初期即实施周期注水的效果最好;塔河油田数值模拟研究表明周期注水开发效果明显好于依靠天然能量、连续注水的效果,其优点是既保持地层能量,避免注入水的突进,同时又充分利用毛管自吸驱油作用,周期注水是很好的提高采收率方法。  相似文献   

伴随数据同化法反演涌潮河口开边界   总被引：4，自引：1，他引：3       下载免费PDF全文

陈耀登  王如云  李未  卢长娜 《水科学进展》2007,18(6):829-833

构造了非线性守恒型浅水方程的伴随方程,并给出无结构三角网格的开边界校正表达式,利用Godunov格式和Riemann间断解Roe通量格式的设计思想,建立了无结构三角网格有限体积法的伴随开边界反演模型。进行了概化涌潮河口和钱塘江涌潮河口M2分潮开边界反演的数值实验,经过同化得到开边界上振幅的平均误差分别为0.000 6 m和0.053 3 m,证实了本文构造有限体积伴随模型的可行性,也表明本模型能够适应间断解问题。  相似文献   

Modelling hydraulic and capillary-driven two-phase fluid flow in unsaturated concretes at the meso-scale with a unique coupled DEM-CFD technique     

Marek Krzaczek  Michał Nitka  Jacek Tejchman 《国际地质力学数值与分析法杂志》2023,47(1):23-53

The goal of the research was to demonstrate the impact of thin porous interfacial transition zones (ITZs) between aggregates and cement matrix on fluid flow in unsaturated concrete caused by hydraulic/capillary pressure. To demonstrate this impact, a novel coupled approach to simulate the two-phase (water and moist air) flow of hydraulically and capillary-driven fluid in unsaturated concrete was developed. By merging the discrete element method (DEM) with computational fluid dynamics (CFD) under isothermal settings, the process was numerically studied at the meso-scale in two-dimensional conditions. A flow network was used to describe fluid behaviour in a continuous domain between particles. Small concrete specimens of a simplified particle mesostructure were subjected to fully coupled hydro-mechanical simulation tests. A simple uniaxial compression test was used to calibrate the pure DEM represented by bonded spheres, while a permeability and sorptivity test for an assembly of spheres was used to calibrate the pure CFD. For simplified specimens of the pure cement matrix, cement matrix with aggregate, and cement matrix with aggregate and ITZ of a given thickness, DEM/CFD simulations were performed sequentially. The numerical results of permeability and sorptivity were directly compared to the data found in the literature. A satisfactory agreement was achieved. Porous ITZs in concrete were found to reduce sorption by slowing the capillary-driven fluid flow, and to speed the full saturation of pores when sufficiently high hydraulic water pressures were dominant.  相似文献   

基于地表温度—植被指数三角/梯形特征空间的地表蒸散发遥感反演综述     

唐荣林  王晟力  姜亚珍  李召良  刘萌  唐伯惠  吴骅 《遥感学报》2021,25(1):65-82

地表蒸散发是地表水分循环和能量平衡的重要组成成分,其准确估算对农业灌溉与干旱监测、水资源管理、气候变化预估等研究至关重要.基于地表温度—植被指数三角/梯形特征空间开展地表蒸散发遥感反演及土壤蒸发/植被蒸腾分离是地表蒸散发定量遥感研究的国际热点与前沿课题之一.本文全面、系统、深入地综述了地表温度—植被指数三角/梯形空间反...  相似文献   

HⅢ(2n)中元素的一种标准化表示     

沈雁 《大气科学学报》1997,20(4):487-492

给出HⅢ(2n)中元素的一种标准化表示,HⅢ(2n)={Z∈C^2n×2n|1/2(Z+Z'')>0,ZJ=JZ''},J=0 I_n-I_n 0,1/2(Z+Z)>0表示矩阵1/2(Z+z'')是正定的。  相似文献