Predicting Visual Perception of Material Structure in Virtual Environments

One of the most accurate yet still practical representation of material appearance is the Bidirectional Texture Function (BTF). The BTF can be viewed as an extension of Bidirectional Reflectance Distribution Function (BRDF) for additional spatial information that includes local visual effects such as shadowing, interreflection, subsurface‐scattering, etc. However, the shift from BRDF to BTF represents not only a huge leap in respect to the realism of material reproduction, but also related high memory and computational costs stemming from the storage and processing of massive BTF data. In this work, we argue that each opaque material, regardless of its surface structure, can be safely substituted by a BRDF without the introduction of a significant perceptual error when viewed from an appropriate distance. Therefore, we ran a set of psychophysical studies over 25 materials to determine so‐called critical viewing distances, i.e. the minimal distances at which the material spatial structure (texture) cannot be visually discerned. Our analysis determined such typical distances typical for several material categories often used in interior design applications. Furthermore, we propose a combination of computational features that can predict such distances without the need for a psychophysical study. We show that our work can significantly reduce rendering costs in applications that process complex virtual scenes.     

Realizing 3D Visual Programming Environments within a Virtual Environment

In the visual programming community, many interesting graphical metaphors have been reported upon for representing computer programs graphically. Most of them have a 2D or 2.5D appearance on the screen in order to reflect the inherent multi-dimensionality of the programming constructs being represented. By going into a three-dimensional representation, this reflection can go a stepfurther. With ever increasing3D graphics rendering capabilities on todays computers, it moreover becomes feasible to extend the dimensionality of the program (and data structure) depiction. We follow this approach by realizing 3D graphical programming techniques within CAEL, our interactive Computer Animation Environment Language. The paper elucidates how several concepts, traditionally found within the Virtual Environments area, can be utilized in the realization of three-dimensional Programming Environments.     

虚拟环境中基于视觉心理学原理的预见性纹理绘制算法

本文首先阐述了视觉心理学原理 ,然后对基于视觉心理学原理的预见性纹理绘制算法进行了详细的研究。采用本算法可以生成符合人眼视觉感知的虚拟场景。     

虚拟计算环境中的虚拟网络

虚拟计算环境是近年来的学术研究热点,而虚拟网络是构成虚拟计算环境的核心技术。本文介绍了主流的虚拟网络构成原理和虚拟网络实现技术,分析了虚拟计算环境中虚拟网络的特点,总结并提出了虚拟网络的性能开销、QoS、自适应和安全性等开放性问题。     

虚拟环境中的计算时延

初步研究了虚拟环境中计算时延的特性,从能量传输的角度讨论了计算时延对虚拟环境稳定性的影响,并设计了一个虚拟阻尼器以抵消计算时延产生的多余能量,从而保证虚拟环境的无源稳定性.     

Reflective Interaction in Virtual Environments

The proliferation of projection-based systems in recent years resulted in a variety of specialised interaction techniques that make Virtual Environments a better man machine interface. However, the success of these techniques and metaphors is directly linked to the interaction and tracking devices used in their implementation. Users find that devices such as the data glove, stylus or joystick can be expensive and cumbersome especially for the inexperienced. A variety of approaches exist that make use of computer vision for tracking gestures or for achieving wireless interaction. Typically these approaches involve the use of a two- camera pair, or a stereoscopic camera.
Our approach uses only one camera and one or more reflective surfaces, to effectively and accurately calculate 3D information. The calibration time is minimal and it allows for a very flexible positioning of the camera and reflecting surfaces. Wireless interaction and natural interaction metaphors in the user's physical space can be created using our method. The method can be combined easily and effectively with projection-based systems as well as with standard and stereoscopic monitors, or extended for the use in augmented spaces. It is an inexpensive method that uses commonly available hardware and therefore its application areas as an interaction and tracking device, include games and use of virtual environments in education. In this paper, we describe the method and its use as an interaction device in two applications, and conclude with a discussion on its advantages and limitations.     

An Investigation of Visual Cues used to Create and Support Frames of Reference and Visual Search Tasks in Desktop Virtual Environments

Visual depth cues are combined to produce the essential depth and dimensionality of Desktop Virtual Environments (DVEs). This study discusses DVEs in terms of the visual depth cues that create and support perception of frames of references and accomplishment of visual search tasks. This paper presents the results of an investigation that identifies the effects of the experimental stimuli positions and visual depth cues: luminance, texture, relative height and motion parallax on precise depth judgements made within a DVE. Results indicate that the experimental stimuli positions significantly affect precise depth judgements, texture is only significantly effective for certain conditions, and motion parallax, in line with previous results, is inconclusive to determine depth judgement accuracy for egocentrically viewed DVEs. Results also show that exocentric views, incorporating relative height and motion parallax visual cues, are effective for precise depth judgements made in DVEs. The results help us to understand the effects of certain visual depth cues to support the perception of frames of references and precise depth judgements, suggesting that the visual depth cues employed to create frames of references in DVEs may influence how effectively precise depth judgements are undertaken.     

Grid-Based Visual SLAM in Complex Environments

This paper presents a novel approach to the real-time SLAM problem that works in unstructured indoor environment with a single forward viewing camera. Most existing visual SLAM extract features from the environment, associate them in different images and produce a feature map as a result. However, we estimate the distances between the robot and the obstacles by applying a visual sonar ranging technique to the image and then associate this range data through the Iterative Closest Point (ICP) algorithm and finally produce a grid map. Moreover, we construct a pseudo-dense scan (PDS) which is essentially a temporal accumulation of data, emulating a dense omni-directional sensing of the visual sonar readings based on odometry readings in order to overcome the sparseness of the visual sonar and then associate this scan with the previous one. Moreover, we further correct the slight trajectory error incurred in the PDS construction step to obtain a much more refined map using Sequential Quadratic Programming (SQP) which is a well-known optimization scheme. Experimental results show that our method can obtain an accurate grid map using a single camera alone without the need for more expensive.     

协同虚拟环境的通信体系结构研究

协同虚拟环境是支持多用户进行协同工作的一个共享虚拟空间,为了实现用户之间的协同工作,协同虚拟环境的网络通信体系结构必须满足一致性和可扩展性等要求。该文从网络的拓扑结构、消息过滤机制、数据压缩方法和通信协议等方面对协同虚拟环境的通信体系结构进行了分析和讨论,最后指出了需要进一步研究的方向。     

Multimodal Communication in Inhabited Virtual Environments

This paper reports on ongoing research of various aspects of multi-modal interactions in a Virtual Reality environment in which visitors can interact in diverse ways with agents and objects in the environment. The virtual environment is a copy of a theatre and is inhabited by both embodied and non-embodied agents that can assist the visitor: providing information about the performances, selling tickets, or helping the visitor navigate through the building.Interactions in this environment are typically multimodal. Several agents are capable of natural language interactions with the user. However, because the interactions take place in a virtual reality environment, a lot of information can also be presented visually.     

The Role of Visual Feedback and Age When Grasping,Transferring and Passing Objects in Virtual Environments

ABSTRACT

Visual feedback about one’s own movements can be important for effective performance in natural and computer-generated environments. Previous work suggested that, for young adults, performance in virtual environments was influenced by the presence of a crude representation of the hand in a task-specific fashion. The current study was performed to determine whether this pattern of results holds across the lifespan. Specifically, we were interested in determining whether a representation of the hand is useful for movement performance in children, middle adults, and older adults when they reach to grasp an object, transfer it between their two hands, or receive it from a partner. Surprisingly, visual feedback condition had very little effect on performance in the current experiment, with the exception that participants in all three age groups altered how wide they opened their hand when grasping depending on visual condition. Patterns of reach and grasp performance changed across task depending on age, with older adults displaying different patterns than children and middle-aged adults. These results suggest that feedforward planning and the use of feedback are modulated by both age and task.     

Indoor Human Wayfinding Performance Using Vertical and Horizontal Signage in Virtual Reality

Disorientation has many costs. It may lead to physical fatigue, stress, and frustration and can also jeopardize people's safety. Designing wayfinding aids to fit people's needs can facilitate their environmental knowledge acquisition and, therefore, improve their wayfinding performance. The scope of this article is human wayfinding in unfamiliar buildings, considering only individual pedestrian movement in an immersive virtual environment. The purpose is to investigate the use of external information at a higher level of awareness (e.g., signage) as a wayfinding aid, as well as the use of immersive virtual reality (VR) to study indoor wayfinding. Fifty‐four volunteers accomplished a wayfinding task (i.e., finding a room from the building's entrance) within a virtual building, employing two types of signage systems (i.e., vertical and horizontal conditions). A neutral condition (no signage) was also considered as a control condition to be used as a baseline. Aside from the success of the wayfinding task (getting to the destination), other performance metrics (distance traveled, time spent, number of pauses, and average speed) were analyzed and compared. Although the differences found are not statistically significant, findings suggest that participants assigned to the horizontal condition traveled smaller distances, spent less time, made fewer pauses, and moved at higher average speed than those assigned to vertical and neutral conditions. Gender‐related differences were found statistically significant only in the average speed variable (females were faster than males). © 2012 Wiley Periodicals, Inc.     

The Paradox of Security in Virtual Environments

Virtualization trims administrative overhead, eases system management, and combats OS-level security vulnerabilities. However, it also exhibits new characteristics and exposes new vulnerabilities that can be detrimental to securing the system.     

Managing Mobility of Users in a Virtual Network

Terminal and personal mobility are the fundamental characteristics of Nomadic Computing. However, personal mobility provides a greater degree of flexibility, creating an environment in which a user roams in network without a wireless laptop or a mobile phone and yet enjoys anytime, anywhere network accessibility. This work presents Nomad'sPersonal Access System (NPAS): a software system at OSI application layer that provides a personal mobility environment within a virtual, private network, spanning different organizational networks. It implements dynamic association between a user and shared devices associated with a new location. The dynamic mapping of users to devices is achieved using Internet'sLDAP distributed directory. The LDAP'sdistributed directory provides services and location data to the network—thus incoming and outgoing messages can be easily routed to the current location of a nomad. The ability to know the current location of a nomad increases his/her accessibility to and from other people. Therefore, NPAS also addresses the messaging services and suggests a solution based on agents. This work is motivated by the larger project of the Mobile Agents Alliance, a collaborative effort that includes the National Research Council of Canada, the University of Ottawa, and Mitel Corporation.     

虚拟人行为控制技术在分布式虚拟环境中的实现

在分布式虚拟环境中加入虚拟人的运动时,一方面要考虑行为建模与姿势控制技术的实现,以生成理想的行为动画,另一方面关节,体模型的复杂性导致运动参数在网络上传输的负载增大。如果采用不同层次的参数来描述虚拟人姿势,则可以实现一些高层的行为控制方式,并将参数关键帧技术和逆向运动学技术等各种动画技术有机结合,同时给网络传输参数的选择提供不同的解决方案,文章对采用不同方案带来的网络负载和计算负载进行了定性比较和分析。     

Effects of Visual Cues on Distance Perception in Virtual Environments Based on Object Identification and Visually Guided Action

ABSTRACT

In perceiving a virtual environment (VE), distance perception is important in that it affects users’ behaviors and interactions. This study addresses an on-going issue of virtual reality (VR), distance underestimation within a VE. For this purpose, a 2x2x2x5 mixed design was used with two between-subject variables [visual cue for perception (provided and non-provided) and visual cue for action (provided and non-provided)] and two within-subject variables [response measure (verbal estimation and triangulated blind walking) and distance (1 m, 5 m, 10 m, 20 m, and 35 m)]. Sixty-four undergraduate or graduate students participated in the experiment, and a cube was chosen as the target object. The experimental results showed that visual cues for action mitigated distance underestimation and improved the accuracy of perceived distances. In general, distance underestimation was more obvious in the triangulated blind walking than the verbal estimation, and in the action/vista space than personal space, with relatively lower accuracies. Meanwhile, when visual cue for action were provided, the degree of underestimation decreased significantly with higher accuracy particularly in the triangulated blind walking. Although overestimation was found across all the distances in the verbal estimation, overestimation was found only for the personal distance, and underestimation was found for the action/vista distances in the triangulated blind walking. In both response measures, the accuracy of distance perceptions were the worst in the 10 m condition. These findings can be expected to provide insight into the problem of distance underestimation and can help guide design of VEs.     

Handling of Virtual Contact in Immersive Virtual Environments: Beyond Visuals

This paper addresses the issue of improving the perception of contact that users make with purely virtual objects in virtual environments. Because these objects have no physical component, the user's perceptual understanding of the material properties of the object, and of the nature of the contact, is hindered, often limited solely to visual feedback. Many techniques for providing haptic feedback to compensate for the lack of touch in virtual environments have been proposed. These systems have increased our understanding of the nature of how humans perceive contact. However, providing effective, general-purpose haptic feedback solutions has proven elusive. We propose a more-holistic approach, incorporating feedback to several modalities in concert. This paper describes a prototype system we have developed for delivering vibrotactile feedback to the user. The system provides a low-cost, distributed, portable solution for incorporating vibrotactile feedback into various types of systems. We discuss different parameters that can be manipulated to provide different sensations, propose ways in which this feedback can be combined with feedback of other modalities to create a better understanding of virtual contact, and describe possible applications.