Zhangye Wang

Real-time snowing simulation

A snowing scene has a unique fascination for people due to its incomparable beauty. However, little work has been presented on the real-time generation of a dynamic snowing scene, partially due to the difficulty that the simulation of a dynamic snowing process involves the complex modeling of the wind field and the interaction between wind and snow. In this paper, by fully considering the physical characteristics of wind and snow, we construct a three-dimensional wind field based on the discrete form of the Boltzmann equation. According to the interaction laws between wind and snow, we simulate the falling of snow, deposition and erosion in 3D space. Experimental results show that realistic wind-driven snow scenes under different speeds of wind with different amounts of snowfall can be rendered in real-time.

A new cloud removal algorithm for multi-spectral images

Multi-spectral images acquired by different image sensors from satellites or aircrafts are often covered with cloud under bad weather condition. In this paper, we propose a new cloud removal method to restore the cloud-covered area of multi-spectral images using only a couple of multi-spectral images taken of the same scene. In our algorithm, we take the registered visual and infrared images as an example. We first de-noise the two images with the method of Wiener Filter to wipe off the primary noise. As the infrared imaging has more powerful ability of penetrating through cloud than the visual image, we adopt the method of Poisson Matting to exactly segment the edge of area covered by infrared cloud and use wavelet analyzing to restore the area originally occupied by infrared cloud. Then a B-spline based model is hired to repair the residual holes. For the corresponding visual image of the same scene by taking the spacial correlation between the two multi-spectral images, the location of targets under visual cloud is reconstructed and their texture styles are finally recovered by colorization method. Our algorithm is easy to manipulate and can also be extended to other multi-spectral wavebands.

A novel visual analytics approach for clustering large-scale social data

Social data refers to data individuals create that is knowingly and voluntarily shared by them and is an exciting avenue into gaining insight into interpersonal behaviors and interaction. However, such data is large, heterogeneous and often incomplete, properties that make the analysis of such data extremely challenging. One common method of exploring such data is through cluster analysis, which can enable analysts to find groups of related users, behaviors and interactions. This paper presents a novel visual analysis approach for detecting clusters within large-scale social networks by utilizing a divide-analyze-recombine scheme that sequentially performs data partitioning, subset clustering and result recombination within an integrated visual interface. A case study on a microblog messaging data (with 4.8 millions users) is used to demonstrate the feasibility of this approach and comparisons are also provided to illustrate the performance benefits of this approach with respect to existing solutions.

Dynamic modeling and rendering of grass wagging in wind

Simulation of dynamic natural scene is one of the most challenging tasks in computer graphics. In this paper, we propose a new approach to dynamic modeling and rendering of grasses wagging in wind. Through length preserving free‐form deformation of the 3D skeleton lines of each grass blade and using the alpha test to implement transparent texture mapping, we successfully model grasses of different shapes with rich details. To simulate the real time waggle of grasses, the grasses of a meadow are represented in LOD, while their skeleton lines are dynamically deformed according to some physical models. Simplification technique is also employed to accelerate the collision detection between neighboring grasses. Experiments show that our method can realistically render the animated grass scenes under wind of different speeds and types in real time. Copyright

Real time simulation of a tornado

We present a novel method for simulating a tornado scene and its damage on the environment in real time, which is recognized as a challenging task for researchers of computer graphics. The method adopts a Reynold-average two-fluid model (RATFM) for modeling the motion of a tornado. In RATFM, the air flow (wind field) is simulated by Reynold-average Navier–Stokes equations. The motion of dust particles is approximated as a continuous fluid and is modeled by non-viscosity Navier–Stokes equations. An interaction force is introduced to simulate the interaction between these two-fluid systems efficiently. Considering the data structure of our method, we design a RATFM solver on the GPU to achieve real time simulation. We also adopt new features of the GPU to accelerate our algorithm. Then, an efficient method is proposed to simulate the tornado’s interaction with surrounding large objects such as a car, a bus, a house, etc. In our model, the objects in the tornado scene are represented by connected voxels and a corresponding graph storing the link information. Compared with the photographs of real tornado displays, our simulated results are quite satisfactory.

Simulation of atmospheric binary mixtures based on two-fluid model

Atmospheric binary mixtures such as tornado, sandstorm are common natural phenomena in our daily life. There are two fluid systems in these phenomena, which are air flow (wind field) and dust particle flow. Due to the complex mechanism of two fluid systems and the interaction between them, few works have been done on simulating these phenomena. In this paper, for the first time, we have simulated such two fluid phenomena under a unified framework by a Reynolds-average two-fluid model (RATFM) based on the Navier-Stokes equations. In RATFM, the air flow and dust particle flow are simulated accurately by two different Navier-Stokes equations, respectively. The interaction between two fluids is also simulated by introducing an interaction force. Then, a RATFM solver on GPU is designed to achieve fast simulation. In addition, multiple scattering effects of the participating media are considered for realistic rendering.

Dynamic modeling and rendering of grass wagging in wind: Natural Phenomena and Special Effects

Not everything is perceived as it is provided by the environment. Depending on focus and attention perception can vary and therefore also the knowledge about the world. Virtual humans are sensing the virtual world, storing knowledge and using it to perform tasks. This paper describes our approach to model perceiving, storing and forgetting knowledge as the main regulation of tasks. We use different forms and levels of knowledge which can be independently adapted to different personalities and situations by combining computer graphics methods with psychological models. Copyright

Real-time adaptive fluid simulation with complex boundaries

In this paper, we present a new adaptive model for real-time fluid simulation with complex boundaries based on Smoothed Particle Hydrodynamics (SPH) framework. Firstly, we introduce an adaptive SPH framework that is based on our character field function composed of four factors: geometrical complexity, boundary condition, physical complexity, and complementary condition in terms of the neighboring particle number. Meanwhile, the rule for particle adaptation is presented. We also present a two-step method to fast detect collision with complex boundary. The first step is voxelization on the complex scene. In the second step, based on the result of voxelization, we propose a three-phase method to fast detect collisions between complex boundaries and particles. By using this method, we avoid most of the useless intersection detection computation and greatly enhance the computation efficiency. In addition, a subdivision of boundary is precomputed before the collision interaction method so that fluid in a scene with complex boundary can still be simulated at relatively high speed and system stability risk is reduced greatly. To further accelerate the simulation, a highly parallel fluid algorithm is presented and implemented using GPU so that we can simulate dynamic fluid with mutual interaction between fluid and complex boundary at a considerably fast speed without compromising realism.

Real-time foveation filtering using nonlinear Mipmap interpolation

In recent years, several techniques have been proposed to simulate the gaze effect of the Human Visual System (HVS). It is believed that this effect is due to the foveation filtering. Current techniques to simulate the foveation filtering in computer graphics are either slow or suffer from artifacts and limitations. In this paper, we present a new approach of foveation filtering based on the Mipmap Pyramid of the current view by considering the relationship between the Gaussian kernel and Mipmap level. Due to the nonlinear Mipmap interpolation under the Bilateral Filtering scheme, we are able to simulate the foveation filtering more naturally and efficiently than in previous work. Moreover, a detail enhancement method based on the Cornsweet illusion is proposed to augment the gazing effect. We demonstrate our new approach with a variety of examples and provide comparisons with recent approaches.

Infrared image synthesis for bridges

Recently infrared signature simulation has been in a state of great interest. Although various models have been developed to generate synthetic image of infrared scenes, little work has been done to create high fidelity infrared image of bridge. In this paper a realistic model for infrared image synthesis of bridge based on its thermal energy transmission is proposed to generate the infrared image of bridge at different time. Our new IR image synthesis model of bridge accounts for meteorological, environmental, material and artificial factors. Then an energy equilibrium equation is built based on the principle of heat transfer and infrared physics. And a finite difference method is adopted to solve the equations. Finally we get the radiance distribution of target surface. To get high fidelity, the effect of atmosphere is added using LOWTRAN model. The value of attenuation is pre-computed and stored in our database. We also pre-generate infrared texture and depth attenuated image from visible image. Infrared images of bridge from different viewpoints at different time can be rendered. Our results of simulation show that the model is robust and feasible.