利用近景摄影测量制作日照分析用图

随着城市化进程日益加快,人民生活水平不断提高,住房的日照采光逐渐被人们所重视。在为居民、开发商以及相关管理部门提供科学、规范的房屋采光情况时,日照分析起着举足轻重的作用。而如何快速、准确、高效地制作日照分析所需的用图,已经成为日照测量中亟待解决的问题。传统的日照分析用图制作是基于电子全站仪和水准仪实现的,制作过程简单,外业工作量大。本文探讨利用近景摄影测量方法制作日照分析用图,并通过理论和实践证明此方法可行。     

环焦天线日照温度场数值分析

日照产生的温度载荷是影响天线性能的主要因素之一,获取天线的日照温度场特性对于天线结构研究与性能维护十分重要。针对现有温度场研究缺乏环焦天线案例问题,仿真计算了9:00～16:00时间段某12 m天线的日照温度场。分析了该天线部件之间的温差现象和主反射面与背架全天逐小时温度变化趋势。结果表明：天线部件间接收热量与热物性参数的差异会造成部件间温差较大;天线结构之间的互相遮挡会造成结构内部产生明显温度梯度;部件内部温差与温度分布均匀程度有关。     

虚拟城市仿真平台日照分析方法的研究和实现

随着城市建设的高速发展,城市规划设计中如何合理地规划建筑,保证日照质量是城市规划设计中必须考虑的问题.为了更好地对建筑物日照环境进行分析评估,研究了日照基本原理,提出了一种直观的日照分析显示方法.该方法利用OpenGL中的模板缓存技术,通过多次绘制并叠加来实现.通过Visual C++环境,在实验室自主研发的虚拟城市仿真平台(VRGIS)中实现了相应的日照分析功能.实验结果表明,该方法直观有效,在城市规划领域中取得了显著效果.     

基于数码城市GIS的日照分析系统的设计与实现*

针对传统的基于CAD平台的日照分析系统不能适应城市规划与管理快速发展的需求,提出了将城市规划中的各种信息在统一的数据库平台上进行组织与管理,以数码城市GIS及其他技术为核心,并在此基础上整合日照分析的应用专题及其他应用专题的思路。特别对涉及到的关键技术包括三维数据模型的设计、基于Oracle的数据库管理、CAD数据的嵌入与操作、日照分析技术、组件式GIS技术等进行了详细的介绍。最后对基于数码城市GIS软件CCGIS日照分析系统CCSunAnalysis的实现与应用作了简要介绍。     

海量散乱点的曲面重建算法研究

基于海量散乱点的曲面重建在机械产品测量造型、计算机视觉、根据切片数据的医学图像重建等领域中有重要应用.给出了一种以物体表面上不附加任何几何和拓扑信息(包括测点法矢、曲面边界信息)的散乱点集为处理对象,自动生成物体表面的三角网格模型的算法.该算法首先根据测点的邻近测点估算曲面在该测点处的法矢,并采用优化的顺序对法矢方向进行调整以使各测点处的法矢都指向曲面外侧,最后用步进立方体算法输出三角网格模型.采用新的方法计算切平面,不但进一步提高了效率,而且改善了曲面边界及尖锐棱边区域的重建效果.还提出并解决了法矢方向传播中可能出现的局部“孤岛”问题.同时,提出了一种对海量数据进行空间划分的算法,从而大大提高了海量数据的处理效率.应用实例表明,算法效果良好     

未知曲面数控加工干涉区域求取算法研究

质量和效率是自由曲面零件数控加工所追求的一对相互矛盾的目标，曲面的分片加工可以较好地解决这这一问题，而自由曲面零件分片加工方法中一个关键问题是如何求取自由曲面的干涉区域，提出了在对自由曲面密集采样测量的基础上，利用未知曲面测点信息，通过参数曲面局部逼近和干涉区域测点问几何关系遍历求取干涉区域的算法，该方法避开了烦琐的自由曲面重建处理，仿真和实验研究的结果验证了算法的有效性。     

组合体太阳帆板遮挡分析及可视化

组合体太阳帆板遮挡分析是航天器在轨能源持续性评估的重要依据.针对电能效率与光照有关,提出一种太阳光线与航天器体素的各个面一一求交点的算法,即“穿点判断法”.算法具有数据输出和可视化特点.首先通过几何学的方法建立了组合体太阳帆板遮挡简化数学模型,并对太阳帆板采用四叉树递归划分,考虑了组合体本体对帆板以及帆板对帆板的遮挡情况,然后应用一元二次方程求根法来判断帆板是否被遮挡,最后通过设定帆板最小粒度来计算帆板的遮挡面积,并用OpenGL对遮挡情况进行可视化显示.仿真结果表明,方法能够有效地解决方程可以描述的任何体素如圆柱、圆台、圆锥、球以及用标准化的体素构造复杂的几何形体等航天器的太阳帆板遮挡问题.     

旋转圆锥网格及其在玻璃/钢结构中的应用

圆锥网格是计算机辅助建筑设计中一类新的平面四边形网格,具有良好的等距性质,非常适用于玻璃/钢结构,而旋转曲面是建筑设计中的常用形状.通过引入旋转圆锥网格的概念,并利用圆锥网格的定义,给出了构造旋转圆锥网格的简单方法.证明了只在旋转曲面r(u,v)=(f(u)cosv,f(u)sinv,g(u))的v参数方向进行均匀分割,而在U参数方向进行任意分割,则所产生的平面四边形网格为圆锥网格;并研究了旋转曲面为圆锥曲面和圆柱曲面的特殊情况;最后给出了基于旋转圆锥网格的玻璃结构造型实例.该方法简单易行,对计算机辅助建筑设计中的玻璃/钢结构造型有一定的实际应用价值.     

基于静力测试的三维曲面结构测点优化配置

传感器测点优化配置在结构健康监测系统中具有重要作用。针对结构健康监测中静力作用下三维曲面结构变形状况进行了研究,提出了三维曲面结构的测点优化配置方法。首先,对三维曲面结构进行测点组合选取,根据已知测点的响应值采用三维超曲面样条函数插值估计未布置测点的响应值,然后建立适应度函数,对未布置测点的估计值与实际值的误差进行判定,最后通过二重结构编码遗传算法对测点组合进行优化,选取适应度函数值最小的测点配置方案,从而实现了传感器测点优化配置的目的。应用该方法对简支的圆柱壳弯曲变形进行了测点优化配置,得到的适应度函数值最小的测点配置方案中,未布置测点的估计值与实际值的误差为1.10％,从而验证了该方法的可行性和有效性。     

针对规则化工件曲面的喷涂轨迹规划研究

基于大曲率复杂自由曲面可被分片造型成若干个近似平面、圆柱面、圆锥面和球面组合的思想,文中分别针对平面、圆柱面,圆锥面、球面等不同规则化曲面的喷涂轨迹优化进行研究。首先根据平面的静态喷涂模型分别建立圆柱面、圆锥面、球面的喷涂模型,并以涂层均匀性为优化目标求解优化的路径参数,喷枪速度v和喷涂间距d,在此基础上分别给出针对平面、圆柱面、圆锥面、球面的喷枪轨迹的生成算法。最后通过仿真验证了所提方法的有效性、正确性。     

从遮挡边缘和局部阴影恢复表面形状

遮挡边缘和局部阴影是表面形状估计的重要线索。本文利用不同视点下的遮挡边缘序列，获取它们所对应的表面点的三维几何关系。并结合局部阴影分析，对物体表面的非暴露区域进行深度（高度）计算。最终通过插值，获得表面三维模型，实现真实目标建模。     

融合阴影图和深度划分阴影体的阴影渲染算法

阴影图算法可以简单、快速地渲染硬阴影,但该算法渲染的硬阴影会在边缘区域出现锯齿状走样。受此影响,基于阴影图算法渲染的柔和阴影,在小尺寸半影区域依然可能会出现锯齿状走样。因此,要渲染无走样的柔和阴影,需要精确计算阴影边缘区域的着色点对点光源的可见性。深度划分阴影体算法可以精确地计算着色点对点光源的可见性,但其不仅在效率上不及阴影图算法,还无法实现柔和阴影渲染。针对上述问题,提出一种融合阴影图和深度划分阴影体的阴影渲染算法,对处于阴影边缘区域的着色点,使用深度划分阴影体算法精确计算该着色点对点光源的可见性;对其他着色点,使用阴影图算法快速计算该着色点对点光源的可见性。最后,将着色点的可见性值存储在可见性图中并滤波即可实现无走样柔和阴影的渲染。     

Specular Lobe‐Aware Filtering and Upsampling for Interactive Indirect Illumination

Although geometry‐aware filtering and upsampling have often been used for interactive or real‐time rendering, they are unsuitable for glossy surfaces because shading results strongly depend on the bidirectional reflectance distribution functions. This paper proposes a novel weighting function of cross bilateral filtering and upsampling to measure the similarity of specular lobes. The difficulty is that a specular lobe is represented with a distribution function in directional space, whereas conventional cross bilateral filtering evaluates similarities using the distance between two points in a Euclidean space. Therefore, this paper first generalizes cross bilateral filtering for the similarity of distribution functions in a non‐Euclidean space. Then, the weighting function is specialized for specular lobes. Our key insight is that the weighting function of bilateral filtering can be represented with the product integral of two distribution functions corresponding to two pixels. In addition, we propose spherical Gaussian‐based approximations to calculate this weighting function analytically. Our weighting function detects the edges of glossiness, and adapts to all‐frequency materials using only a camera position and G‐buffer. These features are not only suitable for path tracing, but also deferred shading and non‐ray tracing–based methods such as voxel cone tracing.     

Gradient‐based Interpolation and Sampling for Real‐time Rendering of Inhomogeneous,Single‐scattering Media

We present a real‐time rendering algorithm for inhomogeneous, single scattering media, where all‐frequency shading effects such as glows, light shafts, and volumetric shadows can all be captured. The algorithm first computes source radiance at a small number of sample points in the medium, then interpolates these values at other points in the volume using a gradient‐based scheme that is efficiently applied by sample splatting. The sample points are dynamically determined based on a recursive sample splitting procedure that adapts the number and locations of sample points for accurate and efficient reproduction of shading variations in the medium. The entire pipeline can be easily implemented on the GPU to achieve real‐time performance for dynamic lighting and scenes. Rendering results of our method are shown to be comparable to those from ray tracing.     

二维数据场的多投影面可视化方法

本文提出了一种对二维数据场进行多投影面显示处理的三维可视化方法。这种方法利用纹理映射的原理,采用传统的光照浓淡技术,可以生成平行投影和透视投影下的在平面、柱面、锥面、球面和曲面等多投影面上的三维可视化图像,以更全面地展现二维数据中所蕴含的信息。     

Finger-vein authentication based on deformation-tolerant feature-point matching

A novel method for finger-vein authentication based on feature-point matching is proposed and evaluated. A finger-vein image captured by infrared light contains artifacts such as irregular shading and vein posture deformation that can degrade accuracy of finger-vein authentication. Therefore, a method is proposed for extracting features from vein patterns and for matching feature points that is robust against irregular shading and vein deformation. In the proposed method, curvature of image-intensity profiles is used for feature point extraction because such image profiles are a robust feature against irregular shading. To increase the number of feature points, these points are extracted from any positions where vein shape is non-linear. Moreover, a finger-shape model and non-rigid registration method are proposed. Both the model and the registration method correct a deformation caused by the finger-posture change. It is experimentally shown that the proposed method achieves more robust matching than conventional methods. Furthermore, experiments on finger-vein identification show that the proposed method provides higher identification accuracy than conventional methods.     

Basis image decomposition of outdoor time-lapse videos

In augmented reality, it is essential that the rendered virtual objects are embedded harmonically into the view of the background scenes and their appearance should reflect the changing lighting condition of the real scene to ensure illumination consistency. In this paper, we propose a novel method to solve for the sunlight and skylight basis images of static outdoor scenes from a time-lapse image sequence. It is proved that the resulted basis images encapsulate the geometry and material reflectivity of the scene, correspond to the global illumination effects of the outdoor scene under a unit intensity of the sunlight and skylight. Our method is fully automatic. Unlike previous methods, it gets rid of the constraints that the reflectance of all objects in scenes should be ideal diffuse, or the weather condition should be overcast or sunshine. During decomposition, we first detect shadowed pixels by analyzing the time-lapse curve of each pixel through k-means clustering, the basis images of sunlight and skylight are then solved by an iterative procedure with the decomposition equation. The basis images are further optimized by exploiting their constraints and priors. Experimental results demonstrate the effectiveness and flexibility of the proposed method. Our method can also be applied in image understanding and compressing.     

Time‐Lapse Photometric Stereo and Applications

This paper presents a technique to recover geometry from time‐lapse sequences of outdoor scenes. We build upon photometric stereo techniques to recover approximate shadowing, shading and normal components allowing us to alter the material and normals of the scene. Previous work in analyzing such images has faced two fundamental difficulties: 1. the illumination in outdoor images consists of time‐varying sunlight and skylight, and 2. the motion of the sun is restricted to a near‐planar arc through the sky, making surface normal recovery unstable. We develop methods to estimate the reflection component due to skylight illumination. We also show that sunlight directions are usually non‐planar, thus making surface normal recovery possible. This allows us to estimate approximate surface normals for outdoor scenes using a single day of data. We demonstrate the use of these surface normals for a number of image editing applications including reflectance, lighting, and normal editing.     

Closed Form Solution of Local Shape from Shading at Critical Points

In the theory of shape from shading, behaviours of the local solution around a critical point of the image play an important role. This paper shows that the second derivatives of the object surface can be locally determined at these image critical points. Closed form expressions of the surface second derivatives in terms of the second derivatives of the image brightness and of the reflectance map are shown. They are derived as follows: By differentiating the image irradiance equation twice at an image critical point, a set of polynomial equations is obtained that contains the second derivatives of the surface, of the image brightness and of the reflectance map. Regarding these equations as simultaneous equations for unknown surface second derivatives, they are algebraically solved and their explicit expressions are derived. Such a derivation is possible only at image critical points and is impossible at any other image point. The applicability of the derived expressions to noisy images is tested using synthetic images.