一种基于图像的非均匀单散射参与介质建模方法

针对非均匀单散射参与介质建模问题,提出一种能够保持密度场空间变化细节的建模方法.使用体数据、吸收和散射系数之比分别描述参与介质空间变化的密度分布及光线在其内部的传输特性,通过构建采集图像像素值与它们之间的表达式,将建模问题转化为非线性数值优化问题,求最优解.为了解决高分辨率体数据下大量体素密度值同时求解带来的时间开销大及数值不稳定问题,提出一种符合采集图像像素值明暗分布规律的密度场体数据初始化算法和一种多分辨率体数据逐步求精优化算法;为了快速计算大量体素密度值梯度,提出一种基于GPU的多体素并行梯度计算算法.实验结果表明,提出的方法能够根据采集图像重构烟模型,并保持其细节信息.     

Interactive rendering of globally illuminated scenes including anisotropic and inhomogeneous participating media

Although new graphics hardware has accelerated the rendering process, the realistic simulation of scenes including participating media remains a difficult problem. Interactive results have been achieved for isotropic media as well as for single scattering. In this paper, we present an interactive global illumination algorithm for the simulation of scenes that include participating media, even anisotropic and/or inhomogeneous media. The position of the observer is important in order to render inhomogeneous media according to the transport equation. Previous work normally needed to be ray-based in order to compute this equation properly. Our approach is capable of achieving real time using two 3D textures on a simple desktop PC. For anisotropic participating media we combine density estimation techniques and graphics hardware capabilities.     

Solid modeling of fossil small mammal teeth

This paper presents an approach to create solid models of fossil small mammal teeth using a combination of microcomputed tomography, object based image analysis and voxel modeling. Small mammal teeth, because of their durability, are widely found in Cenozioc sediments the world over and play a key role in stratigraphy as well as in researching the rapid evolution and the paleogeographic spreading of small mammals. Recent advances in microcomputed tomography make this non-destructive analysis method an ideal data source for high-resolution 3D models of fossil small animal teeth. To derive internally consistent solid models of such fossils from micro-CT imagery, we propose a combination of 3D object based image analysis and solid modeling. Incorporating paleontological expert knowledge in the image processing cycle, object based image analysis yields topologically consistent image stacks classified by the main tooth components—enamel, dentine and pulp. Forwarding these data to a voxel modeling system, they can be quantitatively analyzed in an unprecedented manner: going beyond the possibilities of the state-of-art surface models, solid models are capable of unambiguously portraying the entire object volume—teeth can be peeled by material properties, subvolumes can be extracted and automatically analyzed by Boolean operations. The proposed method, which can be flexibly extended to handle a range of paleontological and geological micro-objects, is demonstrated with two typical fossil small mammal teeth.     

一种基于图像的室外场景天气模拟技术框架

文中给出了一个基于图像的室外场景的天气模拟技术框架,该方法仅需要少量的参考图像,结合一定的光照模型模拟生成同一时刻,同一视点,不同天气条件下的室外场景图像,其中不需要场景中物体的几何形状和表面反射特性的信息,给出了模拟生成的结果,说明了该方法的有效性。     

Image-based tree modeling from a few images with very narrow viewing range

Creating 3D tree models from actual trees is a task receiving increasing attention. Some approaches have been developed to reconstruct a tree based on a number of photographs around the tree, typically spanning a wide viewing range. However, due to the environmental restrictions, sometimes it is quite difficult to capture so many acceptable images from so many different viewpoints. In this paper, we propose a tree modeling system which is capable of reconstructing the 3D model of a tree from a few images with very narrow viewing ranges. Because only a few images are required to generate the model, our system has the distinct advantage of fewer environmental restrictions, resulting in the extended usability and flexibility for real applications.

Interactive HDR lighting of dynamic participating media

In this paper, we present two optimization techniques to light and render volumetric data of inhomogeneous participating media. Both are independent of the lighting model selected. We use an implementation of the ray marching algorithm to approximate the Radiance Transfer Equation. The system can calculate single scattering in time-varying isotropic participating media with the incident field being modeled as a high dynamic range (HDR) environment map. We can use dynamic lighting (with certain restrictions) and free camera movement without using any precomputations while achieving interactive frame rates. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.

基于图像表达复杂物体的方法研究

在虚拟现实应用中,传统的建模方法是用图形建模的方法对每一个物体进行建模。在场景中,往往有很多物体是非常复杂甚至难以建模的。为了使建模工作简化并同时保证逼真度,提出一种基于图像表达复杂物体的方法。可以对某个复杂物体拍摄或制作多张对应不同视点方向的图像,并且在程序中用图的数据结构管理。在漫游浏览时,再根据摄像机的当前位置确定显示对应视点方向的图像。这种方法既可保证场景的逼真度,同时又使场景得到简化,使系统的运行速度得到提高。     

Mathematical and computer modeling of dynamic processes in composite media

Problems of vibrations of a representative element of a composite medium with allowance made for the interphase interaction of components are investigated. The results of computer modeling of plane linear and nonlinear problems and also a three-dimensional problem of dynamic equilibrium of a composite system are considered. The surfaces of solutions for various proportions of reinforcing fibers and interphase layers are obtained and analyzed, and the influence of these layers on the character of vibrational processes is investigated. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 5, pp. 127–134, September–October 2008.     

室内虚拟实景空间的自由漫游

在基于图象的虚拟实景空间中自由漫游是目前虚拟现实领域研究的热点，同心圆法是解决空上问题比较好的方法。但是这个方法只解决了柱面投影的问题，用户在垂直方向的视域是固定的，而在室内环境中漫游，用户需要进行俯视和仰视，为此，我们扩展了同心圆法，使用同心球法增加用户的视域范围。     

Numerical modeling and optimization of one-way wave processes in inhomogeneous media

The problem of numerical modeling and optimization of wave processes on the basis of a parabolic Schrodinger-type wave equation with a complex non-self-adjoint operator is considered. An optimality criterion is formulated. Properties of an extremal problem are investigated. A numerical method is proposed for the modeling and optimization of acoustic fields in inhomogeneous domains with piecewise continuous parameters.     

基于图像的建模和绘制技术综述

对基于图像的建模和绘制(IBMR)技术进行综述性介绍，着重阐述IBMR研究的最新进展．文中扼要地回顾了一些基本的IBMR方法，并对这些方法的优点和局限性进行分析比较．最后我们简单介绍IBMR的一些最新研究趋势和可能的应用前景．     

结合法向聚类的大叶片植物重建

根据大叶片植物自身的特性,提出一种从3D点云中重建大叶片植物的方法,主要包括点云聚类和叶片重建两部分.首先根据叶片3D点之间的距离对叶片的3D点云进行初始聚类;然后依据叶子大而平、不同叶片法线方向相差较大的特性,通过计算点的法线将3D点云细分为多个聚类,每个聚类表示一片叶子;最后利用一个通用叶子模型将每个聚类拟合成叶子.实验结果表明,该方法可以重建真实感很强的大叶片植物.     

Mesoscale SPH modeling of fluid flow in isotropic porous media

A novel numerical technique—Smoothed Particle Hydrodynamics (SPH) is used to model the fluid flow in isotropic porous media. The porous structure is resolved in a mesoscopic-level by randomly assigning certain portion of SPH particles to fixed locations. A repulsive force, similar in form to the 12-6 Lennard-Jones potential between atoms, is set in place to mimic the interactions between fluid and porous structure. This force is initiated from the fixed porous material particle and may act on its nearby moving fluid particles. In this way, the fluid is directed to pass through the porous structure in physically reasonable paths. For periodic porous systems formed by intersecting solid material with straight parallel fluid channels, the Kozeny formula of permeability was reproduced successfully, which, to a great extent, validates the reliability of the developed SPH model. Further, SPH simulations for the fluid flows induced by an applied streamwise body force in two-dimensional porous structures of different porosities are performed. The macroscopic Darcy's law is confirmed to be valid only in the creeping flow regime. The derived relationship of permeability versus porosity is compared with some existing numerical results/experimental data, which demonstrates that the present SPH model is able to capture the essential features of the fluid flow in porous media.     

基于平面的建筑物表面模型重建算法的研究

针对建筑物模型的规则性,提出了一种基于平面的建筑物模型重建算法,可以从单幅透视图像恢复建筑物的表面模型．该算法主要分为相机定标、基平面的提取、平面位置和方向的计算等几个子过程．相机定标主要用于求解相机的焦距,是一个非常重要的部分．该算法以建筑物场景中的几何结构作为约束条件,从单幅图像中求解相机的焦距;然后计算基平面位置和法向;最后通过交互式操作指明场景中各平面之间的相互关系,递归求解各平面的位置和法向,达到根据图像重建建筑物场景表面模型的目的．     

虚拟实景空间中的纹理映射技术研究

在传统的纹理映射的基础上,分析了虚拟实景空间中的纹理映射技术的主要特点,并采取图形与图象相结合的方法,以照片作为输入,建立了能自由漫游的虚拟环境,对改进基于图象的渲染作了一些探索。     

一种基于图像的快速点画法

点画法是将微小而密集的点均匀而随机地排列,以点的疏密产生明暗色调和纹理,手工完成点画通常需要耗费艺术家相当长的时间,由计算机生成点画效果是非常有必要的,而其中关键问题就是如何快速合理地产生点的分布。提出一种由数字图像快速生成点画效果的算法,算法能够在不规则区域快速地产生均匀而随机的点。首先根据灰度值将图像划分为多个区域,然后利用密度函数在不同的区域产生不同密度的点,为了能够突出图像特征,对图像的特征区域和非特征区域采用不同的处理方法。实验结果表明利用算法可以快速产生接近人类手工作品的点画。     

基于三幅图像的曲面造型及纹理提取

利用标准的参数曲面来表示真实的三维曲面物体,并将物体正面、侧面及背面拍摄图像的侧影轮廓线作为约束,通过最小化线性约束下的二次目标函数实现曲面造型。将曲面重新投影到物体的正面、背面及侧面图像上,利用基于重心坐标的加权纹理提取方法提取纹理图像。利用真实图像实现了逼真的曲面造型,验证了该方法的可行性和正确性。     

浅析动态图像如何应用于网络媒体设计

随着时代的不断进步,网络技术也得到了前所未有的发展,Adobe Flash在网络上的应用范围也越来越大,而动态图像在网络媒体上表现手法成为吸引浏览者眼球不可缺少的元素,随着人们对网络设计的需求,Flash不仅在网络媒体上被广泛应用,而且也不断地渗透到了其他领域。文章就Adobe Flash的功能及其在网络媒体中的应用进行研究。     

Multi-agent modeling for solving profit based unit commitment problem

Profit based unit commitment problem (PBUC) from power system domain is a high-dimensional, mixed variables and complex problem due to its combinatorial nature. Many optimization techniques for solving PBUC exist in the literature. However, they are either parameter sensitive or computationally expensive. The quality of PBUC solution is important for a power generating company (GENCO) because this solution would be the basis for a good bidding strategy in the competitive deregulated power market. In this paper, the thermal generators of a GENCO is modeled as a system of intelligent agents in order to generate the best profit solution. A modeling for multi-agents is done by decomposing PBUC problem so that the profit maximization can be distributed among the agents. Six communication and negotiation stages are developed for agents that can explore the possibilities of profit maximization while respecting PBUC problem constraints. The proposed multi-agent modeling is tested for different systems having 10–100 thermal generators considering a day ahead scheduling. The results demonstrate the superiority of proposed multi-agent modeling for PBUC over the benchmark optimization techniques for generating the best profit solutions in substantially smaller computation time.