Concepts and characteristics
Virtual reality (virtual reality, referred to as vr), is a kind of immersive interactive environment based on computable information, specifically, it is the use of computer technology as the core of the modern high-tech generation of lifelike visual, auditory, tactile integration of a specific range of virtual environments, the user with the help of the necessary equipment to interact with the objects in the virtual environment in a natural way. The object in the virtual environment to interact, mutual influence, so as to produce "immersed" in the equivalent of the real environment and experience. vr brings a new concept of human-computer interaction, new content, new ways and new methods, making the content of human-computer interaction is richer, more image, the way is more natural and harmonious.
Virtual reality is the crystallization and reflection of the highly developed computer technology in the process of application in various fields, which has the following main features: (1) highly integrated depending on the discipline; (2) human presence; (3) large-scale integration of systems or environments; (4) diversification and standardization of data representation, large capacity of data storage, high-speed data transmission and data processing. distributed and parallelization.
Key technologies
Physical virtualization, virtual reality and high-performance computing processing technology are the three main aspects of vr technology. Physical virtualization is to map the multi-dimensional information of the real world into the digital space of the computer to generate the corresponding virtual world, which provides the necessary information data for high-performance computing processing. Virtual object realization through a variety of computational and simulation techniques to make the computer-generated virtual world of things produced by a variety of stimuli in as natural a way as possible feedback to the user.
1. Physical Virtualization
Physical virtualization mainly includes key technologies such as basic model construction, spatial tracking, sound localization, visual tracking, and point-of-view sensing, which make it possible to generate a realistic sense of the virtual world, and to detect the virtual environment on the user's operation and the acquisition of operation data.
(1) Basic Model Construction Technology
The construction of the basic model is the basis for the application of computer technology to generate the virtual world, which reconstructs the real world object objects in the corresponding three-dimensional virtual world, and saves some of the physical attributes according to the system requirements.
Model construction begins with the creation of a geometric model of the object object, determining its spatial location and the properties of its geometric elements. For example, a 3D geometric model of a product or building is constructed from cad/cam or 2D drawings; a large virtual battlefield is constructed from gis data and satellite, remote sensing, or aerial photos.
In order to enhance the realism of the virtual environment, physical properties and rules of behavior modeling should show the physical properties of the object object such as mass, momentum, material, etc., and follow certain laws of motion and dynamics in the virtual environment.
When geometric and physical models are difficult to accurately portray the real world exists in some special objects or phenomena, according to the specific needs of the use of some special model building methods. For example, meteorological data can be modeled to generate meteorological conditions (cloudy, sunny, rainy, foggy) for virtual environments.
(2) Spatial tracking technology
The spatial tracking of the virtual environment is mainly used to determine the position and direction of the user's head, hands, torso or other manipulatives in the 3D virtual environment through the spatial sensors on the helmet displays, data gloves, data suits, and other interactive devices.
Tracking systems generally consist of transmitters, receivers, and electronic components. There are several types of tracking systems available, including electromagnetic, mechanical, optical, and ultrasonic.
The data glove is a commonly used human-computer interaction device for vr systems, which measures the position and shape of the hand thus realizing the virtual hand in the environment and its manipulation of virtual objects. cyber glove determines the position and orientation of the hand and joints through the bending and twisting sensors on the fingers and the curvature and curvature sensors on the palm of the hand.
(3) Sound tracking technology
Sound tracking of virtual environments using the time difference, phase difference, and sound pressure difference of sounds from different sources arriving at a particular location is an important part of physical virtualization. Acoustic time-of-flight measurements and phase coherence measurements are two basic algorithms that can be implemented for sound location tracking. In a small operation range, the acoustic time-of-flight method can show good accuracy and correspondence. As the operating range increases, the data rate of the acoustic time-of-flight method decreases and is susceptible to pseudo-sound impulses. The phase coherence method is inherently less susceptible to noise interference and allows for the filtering of redundant data without causing hysteresis. However, phase coherence does not directly measure distance but only changes in position and is susceptible to cumulative errors.
Sound tracking generally consists of several transmitters, receivers, and control units. It can be connected to a helmet display or to other devices such as data suits and data gloves.
(4) Visual tracking and point-of-view sensing technology
Visual tracking technology for physical bokeh uses the projection of light from a video camera to an x-y plane array, surrounding light, or tracking light at different moments and locations on the image projection plane to compute the position and orientation of the object being tracked. Visual tracking implementations must consider the tradeoffs between accuracy and range of operation, and designs with multiple emitters and multiple sensors can enhance the accuracy of visual tracking, but make the system complex and expensive.
Point-of-view sensing must be coupled with display technologies, and multiple localization methods (eyepatch localization, helmet displays, remote viewing, and eye-muscle-based sensing) can be used to determine the user's line of sight at a given moment in time. For example, by integrating point-of-view detection and sensing into the helmet display system, pilots can manipulate virtual switches or flight controls at certain times of the day simply by "looking".
2. Virtualization
The key technology to ensure that the user acquires the sensory perceptions of vision, hearing, force, and touch in the virtual environment is the main research content of virtualization.
(1) visual perception
most of the objects or phenomena with a certain shape in the virtual environment, can through a variety of ways to make the user produce a strong sense of reality of the visual perception. crt display, large screen projection, multi-directional electronic wall, stereoscopic glasses, helmet-mounted displays (hmd) and so on are common display devices in the vr system. Different helmet displays have different display technologies, and according to the way the optical image is provided, helmet display devices can be divided into projection and direct vision.
Stereoscopic display technology that enhances the realism of the virtual environment allows the user's left and right eyes to see two flat images with parallax, and synthesize them in the brain to produce stereoscopic visual perception. Helmet displays and stereoscopic glasses are two common stereoscopic display devices. At present, the laser holographic computing based on stereoscopic display technology, laser beams directly on the retina imaging display technology is under research.
(2) Auditory perception
Auditory is second only to the visual perception pathway, the sound effect of the virtual environment, can make up for the lack of visual effects, to enhance the environmental fidelity.
The three-dimensional sound that the user feels helps the user to localize the sound in the operation. The localization of traditional sound models is based on the time difference itd of the sound source reaching the listener's two ears and the pressure difference iid of the sound source to the left and right ears, but it cannot account for monaural localization. Modern sound modeling focuses on describing the propagation of sound from the source to the external ear canal using the head-related transfer function, hrtf, and can support monaural localization. hrtf primarily uses filtering to simulate the head effect, the auricular effect, and the head-masking effect. the nasa air force research center used to place a very small microphone into the artificial ear canal, record the impulse responses of many different sources to the head, and then generate an impulse response for the head according to the hrtf with the impulse results to produce a sense of position in the virtual environment.
(3) Force and tactile perception
One of the key factors in creating "immersion" for participants is the ability of the user to manipulate a virtual object while feeling the reaction force of the virtual object, resulting in tactile and force perception. For example, when you use your hand to pull the gear lever of a car in a virtual driving system, your hand can feel the vibration and tightness of the gear lever.
Force perception is mainly generated by the computer through the force feedback gloves, force feedback joystick on the finger movement damping so that the user feels the direction and size of the force. Because the human force perception is very sensitive, the general accuracy of the device simply can not meet the requirements, and the development of high-precision force feedback device is quite difficult and expensive, which is one of the problems faced by the people.
Without haptic feedback, it is easy for a user to pass his hand through an object in the virtual world when he touches it. An effective way to solve this problem is to add haptic feedback to the user's interaction device. Haptic feedback is mainly based on methods such as vision, air pressure sensing, vibrotactile sensing, electrotactile sensing and neuromuscular simulation. Electronic haptic feedback that feeds variable electrical impulses to the skin and neuromuscular simulation feedback that directly stimulates the cortex are both less safe, while pneumatic and vibrotactile are relatively safer haptic feedback methods.
3. High-performance computing and processing technology
Virtual reality is a modern high-tech computer technology as the core, high-performance computing and processing technology is the key to directly affect the performance of the system. High-performance computing processing technology with high computing speed, strong processing power, large storage capacity and strong networking features mainly includes the following research content:
(1) data conversion and data preprocessing serving the virtualization of physical objects and virtual objects; (2) real-time, realistic graphic image generation and display technology; (3) a variety of sound synthesis and sound spatialization technology; (4) multidimensional information data fusion, data conversion, data compression, data standardization, and database generation; (5) pattern recognition. Such as command recognition, speech recognition, and detection, synthesis, and recognition of gestures and human facial expression information; (6) Research on advanced computational models. Such as expert systems, self-organizing neural nets, genetic algorithms, etc.; (7) distributed and parallel computing, as well as high-speed, large-scale remote network technology.
4. Distributed Virtual Reality
Distributed virtual reality research goal is to establish a multi-user simultaneous heterogeneous participation in the distributed virtual environment, users in different geographic locations as if they were entering into a real world, not subject to physical time and space constraints, through the posture, sound or text, etc. "together!
There are two major camps for distributed virtual reality research. One is distributed virtual reality on the Internet of Nations, such as remote virtual shopping based on the vrml standard. The other is in the high-speed private network invested by the military, such as the use of atm technology of the U.S. military defense simulation Internet dsi.
Application areas
vr technology generation and development, for the solution and deal with a huge amount of money and huge manpower inputs, or have to bear the risk of casualties of a variety of problems provides a new method, the current application of vr technology is mainly focused on the following Several aspects:
1. product design and performance evaluation
Boeing 777 aircraft design is a typical example of the application of virtual prototyping, which consists of 3 million parts, all the design in a virtual environment consisting of hundreds of workstations.
In 1996, the University of California, Berkeley in sgi workstations to realize the school's new building soda hall real-time roaming. China's Beijing University of Aeronautics and Astronautics virtual reality and visualization of new technology research room, also completed the Hengchang garden and its room decoration, virtual Beihang and other roaming system development, is currently for the National Science and Technology Museum to build a Mount Everest and its surrounding environment roaming system.
2. Education and Entertainment
Applying vr technology to education can enable students to visit the seabed, travel in space, observe historical castles, and even go deep into the interior of atoms to observe the trajectory of electrons. Distributed virtual libraries break through the physical time and space limitations and effectively utilize the *** enjoy resources, based on the Internet distributed virtual library has a huge prospect.
vr technology in the entertainment industry has an extremely wide range of applications. The first large-scale vr entertainment system "battletech", each "cockpit" simulator networking for the confrontation between the group, three-dimensional realistic view, joystick, throttle, brake and hit by the shaking of the user's strong sensory stimulation.
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3. Training in difficult and dangerous environments
vr systems serving medical surgical training, using ct or mri data in the computer to reconstruct the geometric model of the human body or an organ, and give certain physical characteristics (such as density, toughness, tissue ratio, etc.), and through the robotic or data gloves and other high-precision interactive tools in the computer simulation of surgical procedures, to achieve the purpose of training, research, and so on. to achieve the purpose of training and research.
The United States nasa and esa (European Space Agency) had successfully applied vr technology to the space activities of space launchers, the free operation of the space station and the maintenance of Hubble space.
4. Distributed Virtual Battlefield Environment
The military field is the earliest research and application of vr technology. The earliest distributed virtual battlefield environment should be 1983 darpa and the U.S. Army *** with the development of simnet research program. From 1994 onwards, the United States darpa and usacom jointly carried out research on the war comprehensive exercise field stow, forming a military exercise environment that includes sea, land and air multiservice, 3700 simulation entities involved, and a geographical range covering 500×750km2.
China from 1996, the national 863 plan support dvenet, by the Beijing University of Aeronautics and Astronautics jointly with Zhejiang University, the National University of Defense Science and Technology, the Armored Corps Engineering Institute, the PLA School of Surveying and Mapping and the Chinese Academy of Sciences Software Institute and other units to develop a distributed virtual environment based information platform. The distributed virtual battlefield environment based on dvenet unites a number of real simulators and virtual simulators distributed in different geographical areas to carry out off-site collaboration and confrontation tactical simulation exercises.
Summary: Virtual Reality is a research field with many unresolved problems and still emerging new problems, and at the same time, it is also a high-tech field full of vitality and with great application prospects. We should and can make a difference in this field