Abstract Visual simulation of fire plays an important role in many applications, such as movies and computer games. In these applications, artists are often requested to synthesize realistic fire with a particular behavior. To meet such requirement, we present a feedback control method for fire simulations. The user can design the shape of fire by placing a set of control points. Our method generates a force field and automatically adjusts a temperature at a fire source, based on user specified control points. Experimental results show that our method can control the fire shape.

Furniture layout design is a challenging problem, and several methods have recently been proposed. Although the lighting environment in a room has a strong relationship with the furniture functionality, the previous methods completely overlooked it in designing furniture layout. This paper addresses this problem; we propose an efficient method for computing furniture layout taking into account the lighting environment. We propose a new cost function that evaluates the lighting environment taking into account inter-reflections of light. A fast method for evaluating the cost function is also proposed. We demonstrate that our method improves the quality and usability of furniture layout by taking into account the lighting environment.

Abstract In this paper, we propose a method for the simulation of clouds using particles exclusively. The method is based on position based fluids, which simulates fluids using position constraints. To reduce the simulation time, we have used adaptive splitting and merging to concentrate computation on regions where it is most needed. When clouds are formed, particles are split so as to add more details to the generated cloud surface and when they disappear, particles are merged back. We implement our adaptive method on the Graphics Processing Unit (GPU) to accelerate the computation. While the splitting portion is easily parallelizable, the merge portion is not. We develop a simple algorithm to address this problem and achieve reasonable simulation times. Copyright © 2015 John Wiley & Sons, Ltd.

Clouds play an important role in creating realistic images of outdoor scenes. Many methods have therefore been proposed for displaying realistic clouds. However, the realism of the resulting images depends on many parameters used to render them and it is often difficult to adjust those parameters manually. This paper proposes a method for addressing this problem by solving an inverse rendering problem: given a non-uniform synthetic cloud density distribution, the parameters for rendering the synthetic clouds are estimated using photographs of real clouds. The objective function is defined as the difference between the color histograms of the photograph and the synthetic image. Our method searches for the optimal parameters using genetic algorithms. During the search process, we take into account the multiple scattering of light inside the clouds. The search process is accelerated by precomputing a set of intermediate images. After ten to twenty minutes of precomputation, our method estimates the optimal parameters within a minute.

This paper presents a method for controlling simulated explosions by prediction and optimization. Many methods have been proposed for simulating realistic explosion based on numerical fluid analysis. These methods are widely used in applications such as movies and computer games. In these applications, there is often a requirement for the explosion to conform to a specified final shape. The goal of our research is to meet this requirement by controlling the simulation so that the explosion evolves into a target shape specified by the user. The key ideas of our method are optimization of the initial velocities at the explosion source and predictive control of the simulation. Our method optimizes the initial velocities during the preprocessing step. Next, during the simulation, it predicts the future shape from the history of the explosion shape and controls the simulation to minimize the difference between the target shape and the predicted shape.

Synthetic images of outdoor scenes generated by computer graphics usually contain the sky as background. The appearance of the sky plays an important role in enhancing the reality of scenes. In this paper, we propose an intuitive and interactive system for synthesizing sky images that can reflect the user's intention. Our system consists of two steps. The first step is a sky generation step. The luminance distribution and colors of the sky are generated using our intuitive user interface. The second step is a cloud composition step. We have prepared a database of photographs of real clouds. Our system searches the database for cloud photographs that are suitable for the synthesized sky. The user selects the clouds in the search results and they are composited into the sky image. By using our system, the user can easily generate desired sky images.

Abstract In this paper, we propose a simple method for modeling clouds from a single photograph. Our method can synthesize three types of clouds: cirrus, altocumulus, and cumulus. We use three different representations for each type of cloud: two‐dimensional texture for cirrus, implicit functions (metaballs) for altocumulus, and volume data for cumulus. Our method initially computes the intensity and the opacity of clouds for each pixel from an input photograph, stored as a cloud image. For cirrus, the cloud image is the output two‐dimensional texture. For each of the other two types of cloud, three‐dimensional density distributions are generated by referring to the cloud image. Since the method is very simple, the computational cost is low. Our method can generate, within several seconds, realistic clouds that are similar to those in the photograph.

Abstract Recently, many techniques using computational fluid dynamics have been proposed for the simulation of natural phenomena such as smoke and fire. Traditionally, a single grid is used for computing the motion of fluids. When an object interacts with a fluid, the resolution of the grid must be sufficiently high because the shape of the object is represented by a shape sampled at the grid points. This increases the number of grid points that are required, and hence the computational cost is increased. To address this problem, we propose a method using multiple grids that overlap with each other. In addition to a large single grid (a global grid) that covers the whole of the simulation space, separate grids (local grids) are generated that surround each object. The resolution of a local grid is higher than that of the global grid. The local grids move according to the motion of the objects. Therefore, the process of resampling the shape of the object is unnecessary when the object moves. To accelerate the computation, appropriate resolutions are adaptively‐determined for the local grids according to their distance from the viewpoint. Furthermore, since we use regular (orthogonal) lattices for the grids, the method is suitable for GPU implementation. This realizes the real‐time simulation of interactions between objects and smoke.

Clouds play an important role for creating realistic images of outdoor scenes. In order to generate realistic clouds, many methods have been developed for modeling and animating clouds. One of the most effective approaches for synthesizing realistic clouds is to simulate cloud formation processes based on the atmospheric fluid dynamics. Although this approach can create realistic clouds, the resulting shapes and motion depend on many simulation parameters and the initial status. Therefore, it is very difficult to adjust those parameters so that the clouds form the desired shapes. This paper addresses this problem and presents a method for controlling the simulation of cloud formation. In this paper, we focus on controlling cumuliform cloud formation. The user specifies the overall shape of the clouds. Then, our method automatically adjusts parameters during the simulation in order to generate clouds forming the specified shape. Our method can generate realistic clouds while their shapes closely match to the desired shape.

Haptic interfaces enable us to interact with a virtual world using our sense of touch. This paper presents a method for realizing haptic interaction with water. Our method displays forces acting on rigid objects due to water with a high frame rate (500 Hz). To achieve this, we present a fast method for simulating the dynamics of water. We decompose the dynamics into two parts. One is a linear flow expressed by a wave equation used to compute water waves. The other is a more complex and non-linear flow around the object. The fluid forces due to the non-linear flow is precomputed by solving Navier-Stokes equations, and stored in a database, named the Fluid Resistance Map. The precomputed non-linear flow and the linear flow are combined to compute the forces due to water.

In a cel animation workplace, nonphotorealistic rendering techniques are often applied to a 3D scene model, which is constructed by referring to the 2D hand-drawn images of the scene. There exist a lot of scene features that must be modeled from the 2D information. The accentuation effects are amongst the most important features in a hand-drawn scene. In this context, accentuation refers to adding hand-drawn shading of the scene. The specific region that an artist wishes the viewer to observe is drawn brighter than the other regions. A method is proposed for the extraction of the accentuation effects from a single 2D painted image of an animated scene. This method enables the automatic addition of the accentuation effects to each frame of the animation, observed from other viewpoints.

In this paper, we propose a radiosity method for the point-sampled geometry to compute diffuse inter reflection of light. Most traditional radiosity methods subdivide the surfaces of objects into small elements such as quadrilaterals. However, the point-sampled geometry includes no explicit information about surfaces, presenting a difficulty in applying the traditional approach to the point-sampled geometry. The proposed method addresses this problem by computing the inter reflection without reconstructing any surfaces. The method realizes lighting simulations without losing the advantages of the point-sampled geometry.

Abstract Sound is an indispensable element for the simulation of a realistic virtual environment. Therefore, there has been much recent research focused on the simulation of realistic sound effects. This paper proposes a method for creating sound for turbulent phenomena such as fire. In a turbulent field, the complex motion of vortices leads to the generation of sound. This type of sound is called a vortex sound. The proposed method simulates a vortex sound by computing vorticity distributions using computational fluid dynamics. Sound textures for the vortex sound are first created in a pre‐process step. The sound is then created at interactive rates by using these sound textures. The usefulness of the proposed method is demonstrated by applying it to the simulation of the sound of fire and other turbulent phenomena. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism ‐ Animation; I.6.8 [Simulation and Modeling]: Types of Simulation ‐ Animation; I.3.7 [Computer Graphics]: Three‐Dimensional Graphics and Realism; I.6.3 [Simulation and Modeling]: Applications; H.5.5 [Information Interfaces and Presentation]: Sound and Music Computing ‐ Methodologies and techniques, Modeling.

We introduce a new deign approach of panoramic movie system. The system, named PanoVi by the authors, captures a 360-degree surround movie from a viewpoint by using four wide-angle video cameras, then the video streams are encoded as a single stream of standard video format. At the viewing side, geometric correction and image mosaicking are performed in real-time by using commodity 3D graphics accelerator hardware equipped with personal computers. By mapping the mosaic on the inside wall in 3D space, the viewing system renders a partial view of arbitrary direction as a virtual environment. This approach is suitable for real-time transmission of a panoramic movie because this system uses a standard video format in transmission layers. We developed a prototype system based on Windows and DirectX8 environments. We confirmed full-rate interactive panoramic movie playback on commodity Pentium4 based PCs.

In computer graphics, most research focuses on creating images. However, there has been much recent work on the automatic generation of sound linked to objects in motion and the relative positions of receivers and sound sources. This paper proposes a new method for creating one type of sound called aerodynamic sound. Examples of aerodynamic sound include sound generated by swinging swords or by wind blowing. A major source of aerodynamic sound is vortices generated in fluids such as air. First, we propose a method for creating sound textures for aerodynamic sound by making use of computational fluid dynamics. Next, we propose a method using the sound textures for real-time rendering of aerodynamic sound according to the motion of objects or wind velocity.

This paper introduces a new panoramic movie system that is applicable for real-time transmission of circle view movies over networks. The system consists of a capturing and a viewing system. The capturing system collects 4 video streams from different directions. After correcting geometric distortion caused by spherical aberration of the lens, these streams are combined into an intermediate video stream. The PanoVi panoramic video format is designed to be compatible with the NTSC and MPEG2 standards. It can be sent to a client system via network and video recording media. At the viewing system, the video stream is decomposed into the original 4 streams and mapped onto walls in 3-space. By indicating viewing direction, the application generates a movie output that appears as if a camera were observing the direction. We developed a prototype of the PanoVi panorama movie system using Pentium III-based PC and confirmed its performance.

A number of methods have been developed for creating realistic images of natural scenes. Their applications include flight simulators, the visual assessment of outdoor scenery, etc. Previously, many of these methods have focused on creating images under clear or slightly cloudy days. Simulations under bad weather conditions, however, are one of the important issues for realism. Lightning is one of the essential elements for these types of simulations. The paper proposes an efficient method for creating realistic images of scenes including lightning. Our method can create photo-realistic images by taking into account the scattering effects due to clouds and atmospheric particles illuminated by lightning. Moreover, graphics hardware is utilized to accelerate the image generation. The usefulness of our method is demonstrated by creating images of outdoor scenes that include lightning.

Recently graphics hardware has increased in capability, and is, moreover, now available even on standard PCs. These advances have encouraged researchers to develop hardware-accelerated methods for rendering realistic images. One of the important elements in enhancing reality is the effect of atmospheric scattering. The scattering of light due to atmospheric particles has to be taken into account in order to display shafts of light produced by studio spotlights and headlights of automobiles, for example. The purpose of the paper is to develop a method for displaying shafts of light at interactive rates by making use of the graphics hardware. The method makes use of hardware-accelerated volume rendering techniques to display the shafts of light.

Modeling free-form shapes in a 3D space is one of the difficult problems in computer graphics. In a parametric patch, intuitive control of free-form shapes is not easy. Modeling methods based on strict physical laws need considerable computation time to deform objects, which are not suitable for interactive applications. In this paper we focus on a cellular automaton and try to apply it to interactive free-form modeling within a 3D voxel space. Each voxel is allocated a finite state automaton which repeats state transitions according to the conditions of its neighbor voxels. Virtual clay objects defined in such an active voxel space are easily deformed under the constraints of physical conservation laws.