Physically Meaningful Rendering using Tristimulus Colours

In photorealistic image synthesis the radiative transfer equation is often not solved by simulating every wavelength of light, but instead by computing tristimulus transport, for instance using sRGB primaries as a basis. This choice is convenient, because input texture data is usually stored in RGB colour spaces. However, there are problems with this approach which are often overlooked or ignored. By comparing to spectral reference renderings, we show how rendering in tristimulus colour spaces introduces colour shifts in indirect light, violation of energy conservation, and unexpected behaviour in participating media. Furthermore, we introduce a fast method to compute spectra from almost any given XYZ input colour. It creates spectra that match the input colour precisely. Additionally, like in natural reflectance spectra, their energy is smoothly distributed over wide wavelength bands. This method is both useful to upsample RGB input data when spectral transport is used and as an intermediate step for corrected tristimulus‐based transport. Finally, we show how energy conservation can be enforced in RGB by mapping colours to valid reflectances.     

Path‐space Motion Estimation and Decomposition for Robust Animation Filtering

Renderings of animation sequences with physics‐based Monte Carlo light transport simulations are exceedingly costly to generate frame‐by‐frame, yet much of this computation is highly redundant due to the strong coherence in space, time and among samples. A promising approach pursued in prior work entails subsampling the sequence in space, time, and number of samples, followed by image‐based spatio‐temporal upsampling and denoising. These methods can provide significant performance gains, though major issues remain: firstly, in a multiple scattering simulation, the final pixel color is the composite of many different light transport phenomena, and this conflicting information causes artifacts in image‐based methods. Secondly, motion vectors are needed to establish correspondence between the pixels in different frames, but it is unclear how to obtain them for most kinds of light paths (e.g. an object seen through a curved glass panel). To reduce these ambiguities, we propose a general decomposition framework, where the final pixel color is separated into components corresponding to disjoint subsets of the space of light paths. Each component is accompanied by motion vectors and other auxiliary features such as reflectance and surface normals. The motion vectors of specular paths are computed using a temporal extension of manifold exploration and the remaining components use a specialized variant of optical flow. Our experiments show that this decomposition leads to significant improvements in three image‐based applications: denoising, spatial upsampling, and temporal interpolation.     

Photoelasticity Raycasting

We present a novel physically‐based method to visualize stress tensor fields. By incorporating photoelasticity into traditional raycasting and extending it with reflection and refraction, taking into account polarization, we obtain the virtual counterpart to traditional experimental polariscopes. This allows us to provide photoelastic analysis of stress tensor fields in arbitrary domains. In our model, the optical material properties, such as stress‐optic coefficient and refractive index, can either be chosen in compliance with the subject under investigation, or, in case of stress problems that do not model optical properties or that are not transparent, be chosen according to known or even new transparent materials. This enables direct application of established polariscope methodology together with respective interpretation. Using a GPU‐based implementation, we compare our technique to experimental data, and demonstrate its utility with several simulated datasets.     

A Dimension‐reduced Pressure Solver for Liquid Simulations

This work presents a method for efficiently simplifying the pressure projection step in a liquid simulation. We first devise a straightforward dimension reduction technique that dramatically reduces the cost of solving the pressure projection. Next, we introduce a novel change of basis that satisfies free‐surface boundary conditions exactly, regardless of the accuracy of the pressure solve. When combined, these ideas greatly reduce the computational complexity of the pressure solve without compromising free surface boundary conditions at the highest level of detail. Our techniques are easy to parallelize, and they effectively eliminate the computational bottleneck for large liquid simulations.     

Implicit Formulation for SPH‐based Viscous Fluids

We propose a stable and efficient particle‐based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second‐ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method.     

淮河流域水质污染时空变异特征分析

选取淮河流域的82个水质监测站,对各站点的1986—2005年水质监测数据进行统计分析,探讨了全流域内水体污染物浓度变化的时空变异特征,为淮河流域水污染治理、水环境保护以及生态修复提供依据。采用时间序列法分析水体污染物浓度的时间变化规律,应用Mann-Kendall检验法对流域范围内水体污染物浓度变化趋势进行了分析。研究结果表明,淮河流域水质变化主要受到入河排污量、上游来水量、闸坝调控方式以及气候条件等方面因素的影响。蚌埠站的水体污染物浓度多年变化规律表明,1995年是水体污染物浓度变化的转折点,1995年前水体污染物浓度不断恶化,1995年后水体污染物浓度逐渐好转。DO浓度的年内变化主要受到水温的影响,表现为冬季浓度高于夏季浓度;CODMn浓度同时受到闸坝调控方式以及区域来水量的影响,汛期浓度低于非汛期。从全流域的水体污染物浓度变化规律看,有机污染物浓度呈显著上升趋势的河段主要分布在淮北支流上,说明在20世纪90年代后期,虽然流域进入相对丰水期以及进行了大规模的水污染联防工作,淮河流域水质污染得到了一定程度的改善。但在2000年后,随着流域内入河污水量和污染物排放量的增加,淮河流域的水质污染依然严重。     

三峡水库航运流量补偿调度效益

三峡水库在枯水季节(简称“枯季”)为下游航运实施流量补偿调度是三峡工程主要设计任务之一。依据初步设计,三峡水库自2006年汛末进入初期运行期以来,开始承担大坝下游航运流量补偿任务,实际运行过程中,根据上游来水情况,充分利用水库调节库容实施航运流量补偿调度。本文对三峡水库蓄水发电以来枯季航运补偿运用进行了分析总结,提出了今后枯季水库运用中应注意的问题。     

城镇河道景观规划设计研究——以都江堰博物馆园区河道景观设计为例

河道景观是城镇振兴的重要资源,开发河道景观对于提升城市环境质量、丰富城市景观内容、促进城市社会经济发展具有重要价值。自20世纪60年代环境改造运动兴起以来,城镇河道景观资源的开发受到普遍重视。出于对防洪、灌溉、航运、城市排水等因素的考虑,我国的城镇河道景观资源开发设计工作起步较晚,并且已有的河道景观开发大都千篇一律,流于形式。总结以往河道景观设计的经验教训,结合都江堰博物馆园区河道景观设计实践,提出城镇河道景观设计的思路和方法。     

城市河流水利风景资源开发研究

城市河流水利风景资源开发具有积极的现实意义,是当地城市旅游的重要组成部分之一。在对水利风景资源进行分类的基础上,构建了城市河流水利风景资源开发评价体系。以广东省肇庆市西江三峡为案例,进行了城市河流水利风景资源开发实证研究。     

关于推进黄河立法工作的思考

经过长期的积累和探索,黄河的立法时机趋向成熟。通过对黄河立法必要性和可行性的分析,论证了黄河流域立法工作的必要和紧迫。同时,论述了黄河立法过程中应遵循的基本原则,并在此基础上对应建立的法律制度提出建议,为解决黄河治理、开发、保护和管理中存在的问题提供思路。