VIRTUAL MODELLING OF SOLID OBJECTS WITH CONSTRAINT-BASED MANIPULATIONS

This paper presents an intuitive approach to precise solid modelling in virtual reality environments. A hierarchically structured model is established to handle the tasks of object definition, object creation, and object rendering with an integrated data structure. Constraints are organized at different levels on different objects and are embedded in the data structure. A constraint reasoning engine is developed to automatically determine allowable motions for precise manipulation of virtual objects with online assistance from constraints. Examples are presented to demonstrate the advantage of precise solid modelling through constraint-based manipulations in virtual environments.

The absence of constraints is one of the major limitations in current Virtual Reality (VR) environments. Without constraints, it is difficult to perform precise 3D interactive manipulations in VR environments and precise solid modelling in VR environments cannot be guaranteed. In this paper, constraints are incorporated into the VR environment for intuitive and precise solid modelling. A hierarchically structured constraint-based data model is developed to support solid modelling in the VR environment. Solid modelling in the VR environment is precisely performed in an intuitive manner through constraint-based manipulations. Constraint-based manipulations are accompanied with automatic constraint recognition and precise constraint satisfaction to establish the hierarchically structured constraint-based data model and are realized by allowable motions for precise 3D interactions in the VR environment. The allowable motions are represented as a mathematical matrix for conveniently deriving allowable motions from constraints. A procedure-based degree-of-freedom incorporation approach for 3D constraint solving is presented for deriving the allowable motions. A rule-based constraint recognition engine is developed for both constraint-based manipulations and implicitly incorporating constraints into the VR environment. A prototype system has been implemented for precise solid modelling in an intuitive manner through constraint-based manipulations in the VR environment.

The absence of constraints when interacting with virtual objects is one of the major limitations in the current Virtual Reality (VR) environments. Without constraints, it is difficult to perform precise interactive manipulations and precise solid modelling in VR environments cannot be ensured. In this paper, constraint-based 3D direct manipulations are acquired through incorporating constraints into the VR environment for intuitive and precise solid modelling. Solid modelling in the VR environment is precisely performed in an intuitive manner through precise constraint-based manipulations. Constraint-based manipulations are accompanied by automatic constraint recognition and precise constraint satisfaction and are realized by allowable motions for precise 3D interactions in the VR environment. The allowable motions are represented as a mathematical matrix for conveniently deriving the allowable motions from constraints. A procedure-based degree-of-freedom incorporation approach for 3D constraint solving is presented to derive the allowable motions. A rule-based constraint recognition engine is developed for both constraint-based manipulations and implicitly incorporating constraints into the VR environment. Some special constraint-based manipulations are also implemented as modelling operations for solid modelling in the VR environment.

This paper presents a constraint-based methodology for intuitive and precise solid modelling in a virtual reality (VR) environment. A hierarchically structured and constraint-based data model is developed to support solid modelling in the VR environment. A constraint reasoning engine is also developed to automatically deduce allowable motions for precise constraint-based 3D manipulations. A prototype system of product modelling has been successfully developed, and experimental results demonstrate the advantage of precise solid modelling through constraint-based manipulation in virtual environments.

With today's virtual reality (VR) systems, it is difficult to create precise assembly models through 3D interactions due to hardware limitations. In this paper, an efficient approach is presented for intuitive and precise assembly modeling in a VR environment. Assembly modelling is performed by precise constraint-based 3D direct manipulations in an intuitive manner. Constraint-based manipulations are accompanied with automatic constraint recognition and precise constraint satisfaction, and are realized by allowable motions for precise 3D interactions in the VR environment. Some special constraint-based assembly operations are constructed for assembly modelling in the VR environment. A method for recognizing the pairs of mating features between assembly components is presented. This method integrates 3D direct manipulations with a feature mating knowledge base and makes the process of recognizing a pair of mating features intuitive. A concept of offset solid is also presented for determining assembly components. A prototype system has been developed for assembly modelling through precise constraint-based manipulations in an intuitive manner in the VR environment.

The study of sense of presence experienced in virtual reality environments has become an important area of research. The continued advancement of immersive technology offers more opportunities to examine how a subject becomes immersed in and interacts with a variety of virtual environments. The primary purpose of this research is to study the sense of presence while interacting with a traditional Virtual Reality Environment (Helmet-based system with a Head-tracking device) and compare it with a virtual reality environment using an Immersive Environment (Spherical-based Visualization environment). Two empirical experiments were investigated in this study, each consisting of thirty-five subjects. A virtual airplane scenario was created and simulated for the participants of both environments. Participants were given several questionnaires after completing the simulation. This study mainly focused on question 9 and 10 of that survey, which dealt with how much the participant felt present in the virtual environment, and if the presence of the real world could still be experienced while in the virtual environment. We found that the subjects felt more involved with the virtual environment while using the Immersive Environment simulation versus using the traditional helmet-based Virtual Reality Environment. There was a statistically significant difference in questions 9 and 10 between the Immersive Environment and traditional Virtual Reality Environment when those questions are considered in isolation. However there was not a significant difference in the total sense of presence between the two environments after analyzing the questions together. The primary differences between the questions were analyzed using the overall mean and the standard deviation. The Immersive Environment has a smaller deviation than the traditional Virtual Reality Environment, implying that the sense of presence response is more concentrated. However, the overall results demonstrate that both environments are almost equally effective, with the Immersive Environment having several slight advantages.

With today’s virtual reality (VR) systems, it is difficult to directly and precisely create and modify objects in a VR environment. This chapter presents an approach for solid modelling in a VR environment. Solid modelling in the VR environment is performed precisely in an intuitive manner through constraint-based manipulations. A hierarchically structured and constraint-based data model is developed to support solid modelling in the VR environment. The data model integrates a high-level constraint-based model for precise object definition, a mid-level constructive solid geometry/boundary representation (CSG/BRep) hybrid solid model for hierarchical geometry abstractions and object creation, and a low-level polygon model for real-time visualization and interaction in the VR environment. Constraints are embedded in the solid model and are organized at different levels to reflect the modelling process from features to parts. Constraint-based manipulations are accompanied with automatic constraint recognition and precise constraint satisfaction to establish the hierarchically structured constraint-based data model and are realized by allowable motions for precise 3D interactions in the VR environment. The allowable motions are represented as a mathematical matrix for conveniently deriving allowable motions from constraints. A procedure-based degree-of-freedom (DOF) combination approach for 3D constraint solving is presented for deriving the allowable motions.

A methodology for solid modelling in a virtual reality environment

A hierarchically structured and constraint-based data model for intuitive and precise solid modeling in a virtual reality environment

The absence of efficient constraint management facilities when interacting with virtual objects is one of the major limitations of current virtual reality (VR) systems for CAD applications. Without constraint management facilities, it is difficult to perform precise interactions with today's 3D input devices and precise solid modeling in the VR environments cannot be ensured. In this paper, a constraint manager is presented for intuitive and precise solid modeling in the VR environment. This constraint manager generates constraint-based 3D direct manipulations for precise solid modeling through incorporating constraints into the VR environment. Constraint-based manipulations are realized by allowable motions for precise 3D interactions in the VR environment. The allowable motions are represented as a mathematical matrix for conveniently deriving allowable motions from constraints. A procedure-based degree-of-freedom incorporation solver for solving 3D constraints is presented for deriving the allowable motions. A rule-based constraint recognition engine is developed for implicitly incorporating constraints into the VR environment.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A hierarchically structured constraint-based data model for solid modelling in a virtual reality environment is presented. The data model integrates a high-level constraint-based model for precise object definition, a mid-level CSG/Brep hybrid solid model for supporting hierarchical geometry abstractions and object creation, and a low-level polygon model for real-time visualization and interaction in the virtual reality environment. Constraints are embedded in the solid model and organized at different levels to reflect the entire solid modelling process from features and parts, to assemblies. This model not only provides precise object definition, but also supports real-time visualization and interaction in the VR environment. Furthermore, it has the potential to obtain precise 3D interactions and precise constraint-based manipulations can be deduced from the data model to carry out precise solid modelling in the VR environment.

Virtual reality environments have many potential applications in medicine, including surgical training, tele-operated robotic surgery, assessment and rehabilitation of behavioural and neurological disorders and diagnosis, therapy and rehabilitation of physical disabilities. Although there is much potential for the use of immersive virtual reality environments in clinical applications, there are problems which could limit their ultimate usability. Some users have experienced side-effects during and after exposure to virtual reality environments. The symptoms include ocular problems, disorientation and balance disturbances, and nausea. Susceptibility to side-effects can be affected by age, ethnicity, experience, gender and physical fitness, as well as the characteristics of the display, the virtual environment and the tasks. The characteristics of the virtual reality system have also been shown to affect the ability of users to perform tasks in a virtual environment. Many of these effects can be attributed to delays between the sampling of head and limb positions and the presentation of an appropriate image on the display. The introduction of patients to virtual reality environments, for assessment, therapy or rehabilitation, raises particular safety and ethical issues. Patients exposed to virtual reality environments for assessment and rehabilitation may have disabilities which increase their susceptibility to certain side-effects. Special precautions therefore need to be taken to ensure the safety and effectiveness of such virtual reality applications. These precautions include minimisation of possible side-effects at the design stage. Factors are identified which are likely to affect the incidence of side-effects during and after exposures, and which need to be understood in order to minimise undesirable consequences. There is also a need for the establishment of protocols for monitoring and controlling exposures of patients to virtual reality environments. Issues are identified which need to be included in such protocols.

With today's virtual reality systems, it is difficult to directly and precisely create and modify complex objects in a virtual reality environment. One of the most important reasons is the absence of a suitable model representation that can efficiently support solid modelling in a virtual reality environment. A hierarchically structured constraint-based data model for solid modelling in the virtual reality environment is presented in this paper. The data model integrates a high-level constraint-based model for precise object definition, a mid-level CSG/B rep hybrid solid model for supporting hierarchical geometry abstractions and object creation, and a low-level polygon model for real-time visualization and interaction in the virtual reality environment. Constraints are embedded in the solid model and are organized at different levels to reflect the process of solid modelling. This data model not only provides precise object definition, but also supports real-time visualization and interaction in the virtual reality environment.

2D Shopping site can only provide people with simple pictures and text messages without interaction and sense of reality.This paper argues how to solve these problems through 3D mall for it will become the future development trend of online shopping.In DVR(distributed virtual reality system) virtual environment virtual environment, the different position of multiple users can interact with the collaborative operation.From three perspectives of building a 3D model, designing an interaction function and creating a website, this paper puts forward a scheme of construction for 3D mall system under the environment of DVR By studying a necessity of the 3D mall。 According to a report which is issued in 2014 Q1 by IT research center of China, we can easily find out that online users have more than 310 million people and online shopping markets scale reaches up to 456.44 billion yuan.It is increased 27.6% than a year ago as shown in figure 1. Obviously, shopping on line has become a new way of consumption。

Impairments in reaching and grasping have been well-documented in patients with post-stroke hemiparesis. Patients have deficits in spatial and temporal coordination and may use excessive trunk displacement to assist arm transport during performance of upper limb tasks. Studies of therapeutic effectiveness have shown that repetitive task-specific practice may improve motor function outcomes. Movement retraining may be optimized when done in virtual reality (VR) environments. Environments created with VR technology can incorporate elements essential to maximize motor learning, such as repetitive and varied task practice, performance feedback and motivation. Haptic technology can also be incorporated into VR environments to enhance the user's sense of presence and to make motor tasks more ecologically relevant to the participant. As a first step in the validation of the use of VR environments for rehabilitation, it is necessary to demonstrate that movements made in virtual environments are similar to those made in equivalent physical environments. This has been verified in a series of studies comparing pointing and reaching/grasping movements in physical and virtual environments. Because of the attributes of VR, rehabilitation of the upper limb using VR environments may lead to better rehabilitation outcomes than conventional approaches.