ISSN:1049-8907    

DOI:10.1002/vis.4340050101

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractRealistic image synthesis of botanical trees has many applications. Since the generation of ‘tree skeletons’ having natural visual impressions is essential to realistic image synthesis, various methods of modelling skeletons, especially growth models, have been presented. However, no one has succeeded in simulating natural tree features which appear in a growth process, such as generation of a round tree crown, a weeping bough, an irregular branching pattern, or regeneration of a crown.This paper demonstrates, by showing several simulated examples, that a growth model having the abilities of heliotropism and dormancy break, which produces shapes of trees adapted to changes in the light environment, is effective in the CG simulation of realistic tree skelet

ISSN:1049-8907    

DOI:10.1002/vis.4340050102

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractRecently, the dynamics of linked articulated rigid bodies has become a valuable tool for making realistic three‐dimensional computer animations. An exact treatment of rigid body dynamics, however, is based on rather non‐intuitive results from classical mechanics (e.g. the Euler equations for rotating bodies) and it relies heavily on sophisticated numerical schemes to solve (large) sets of coupled non‐linear algebraic and differential equations. As a result, articulated rigid bodies are not yet supported by most real‐time animation systems. This paper discusses an approach to rigid body dynamics which is based on (both conceptually and algorithmically much simpler) point mechanics; this gives rise to an asymptotically exact numerical scheme (NSI) which is useful in the context of real‐time animation, provided that the number of degrees of freedom of the simulated system is not too large. Based on NSI, a second scheme (NS2) is derived which is useful for approximating the motions of linked articulated rigid bodies; NS2 turns out to be sufficiently fast to give at least qualitative results in real‐time simulation. In general, the algorithm NS2 is not necessarily (asymptotically) exact, but a quantitative analysis shows that in the absence of reaction forces it conserves angul

ISSN:1049-8907    

DOI:10.1002/vis.4340050103

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSince CG simulation of natural phenomena on the basis of their forms and motions has many applications, such as various landscape designs and special effects in films, it is very important and interesting to develop efficient techniques for their visual simulation. It is especially interesting to produce realistic images and animations of flames and smoke, on account of their complicated patterns of behaviour.Effective simulation methods for flames and smoke are expected to satisfy the following requirements:1The motion of flames or smoke produced in an interaction with obstacles can be simulated.2The motion of flames and smoke can be easily controlled according to scenarios.3The spread of fire can be simulated.Although several useful representation methods have been proposed so far, simulating flames and smoke still remains a challenging problem. In this paper, we first describe our basic two‐dimensional visual simulation method based on particle‐based simulation, but not based on exact physical simulation. Roughly speaking, our method assumes that the images of flames and smoke are basically obtained by visualizing turbulence, that is, the particles of flames and smoke play the role of tracers in the field of turbulence. Next, we present an improved method for simulating the spread of fire and the appearance of smoke produced in an incomplete combustion. Simultaneously, we show several examples of the simulation. Finally, we will touch slightly on further problems for extending the model to one which works in three‐dimensional

ISSN:1049-8907    

DOI:10.1002/vis.4340050104

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractBack‐face culling is a preprocessing technique used in computer graphics to speed up the rendering of polyhedra. In this paper we show how this technique can be modified to reduce unnecessary checking of boundary elements in collison detection for a physical‐based simulation and animation systems. At each time step, we determinea prioriwhich faces cannot be part of the contact between two polyhedra and thus can be culled. In the computer graphics technique, the normal vector of a polygon is compared with the view direction. Here, the normal is compared to one or possibly several relative‐velocity vectors, and the face is culled when its motion is in the opposite direction of the normal vector.We also give an algorithm that takes linear time in terms of the number of faces, and on the average eliminates half of the polygons. Owing to its low computational overhead, when it is used as a front end to a collision detection system, a noticeable improvement in performance can be ach

ISSN:1049-8907    

DOI:10.1002/vis.4340050105

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:1049-8907    

DOI:10.1002/vis.4340050106

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY