Editorial Issue 29.1

Abstract

This issue contains six papers. In the first paper, Kim J. L. Nevelsteen from Stockholm University proposes to sample technologies using grounded theory and obtained a definition for a “virtual world” that is directly applicable to technology. The obtained definition is compared with related work and used to classify advanced technologies, such as a pseudo-persistent video game, a MANet, a virtual and mixed reality, and the Metaverse. The results of this article include: a breakdown of properties that set apart various technologies; a definition that is validated by comparing it with other definitions; an ontology showing the relation of different complimentary terms and acronyms; and, the usage of pseudo-persistence to categories of those technologies that only mimic persistence. In the second paper, Tsung-Yu Tsai, Sai-Keung Wong, Yi-Hung Chou, and Guan-Wen Lin, from National Chiao Tung University in Hsinchu, Taiwan, present a method to solve the problem of congestion in navigation fields for crowd simulation. In their paper, they propose to place crowd monitors at the corners to collect the data such as the movement direction of crowds and crowd densities. Then, the navigation field is adjusted dynamically so that the crowds are led to move away from the congested regions. They also propose a simple data structure for speeding up the collision detection process between agents and objects. Experimental results show that their approach successfully alleviates the congestion problem at the corners. In the third paper, Gang Feng and Shiguang Liu, from Tianjin University - Computer Science and Technology in China describe a new method to drive particle-based SPH fluid to match target shape and deforming fluid shape between different models smoothly, especially when the natural fluid motion must be preserved. To achieve the desired behavior, they first generate control particles by sampling the target shapes and then apply a deformation constraint to each control particle, with its neighboring fluid particles keeping details within its influence region. For the generation of control particles, they divide models into source object and target object, then separately sample them by voxelization method, and generate source control particles and target control particles, respectively. In the fourth paper, Soonhyeon Kwon, Younguk Kim, Kihyuk Kim, and Sungkil Lee, from Sungkyunkwan University, Gyeonggi-do Suwon, Korea, propose a novel heterogeneous volume deformation technique and an intuitive volume animation authoring framework. Their volume deformation extends the previous technique based on moving least squares with a density-aware weighting metric for data-driven importance control and efficient upsampling-based volume synthesis. For user interaction, they present an intuitive visual metaphor and interaction schemes to support effective spatiotemporal editing of volume deformation animation. Their framework is implemented fully on graphics processors and thus suitable for quick-and-easy prototyping of volume deformation with improved controllability. In the fifth paper, Ka-Hou Chan, Wei Ke, and Sio-Kei Im, from Macao Polytechnic, China, propose a method integrating several improvements for the real-time simulation of fluid interacting with deformable bodies. They improve the particle neighbor search in SPH so that the pre-defined scene containers are no longer needed. This improvement can also be applied to the simulation of fluid interacting with other materials, such as rigid and soft bodies. They also propose a two-way coupling method for fluid and deformable bodies, where the particle–mesh interaction is obtained by the ray-traced collision detection method instead of the proxy/ghost particles generation. By using the forward ray-tracing method for both velocity and position, they are able to calculate the coupling forces based on the conservation of momentum and kinetic energy in the particle–mesh interaction. They use Screen Space Fluid Rendering (SSFR) for fluid, and based on that we introduce a screen space refraction rendering method to improve the refraction effect. In the last paper, Xuqiang Shao, from North China Electric Power University, Hebei, China, Wei Wu from Beihang University, Beijing, China and Baoyi Wang, from North China Electric Power University, Hebei, China, propose a nonlinear cloth wetting model to simulate visually realistic cloth wetting phenomena, which takes into account the influence of gravity on all aspects of wetting process. Specifically, in order to model water diffusion in unsaturated cloth, they propose a novel nonlinear saturation constraint of cloth particles which considers the influence of gravity, and then solve it using PBD to stably smooth the saturation field. The dynamic behaviors of the cloth and the water–cloth coupling during the cloth wetting process are modeled by using PBD. Moreover, a water absorption model and a water emission model are proposed to simulate the unsaturated cloth absorbing water and the over-saturated cloth draining water under gravity, respectively.