Concepts and characteristics
Virtual reality (vr) is an immersive interactive environment based on computable information. Specifically, it is to use modern high technology with computer technology as the core to generate a realistic visual, auditory and tactile integrated virtual environment in a specific range. With the help of necessary equipment, users interact with objects in the virtual environment in a natural way, thus generating feelings and experiences of "immersion" in the real environment. Vr brings new concepts, new contents, new ways and new methods of human-computer interaction, which makes the content of human-computer interaction richer and more vivid and the way more natural and harmonious.
Virtual reality is the crystallization and reflection of highly developed computer technology in various fields. It has the following main characteristics: (1) highly integrated depending on disciplines; (2) people present; (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 distributed and parallel data processing.
Key-off technology
Virtual reality, virtual reality and high performance computing technology are three main aspects of vr technology. Virtual reality is to map the multidimensional information of the real world to the digital space of the computer, generate the corresponding virtual world, and provide the necessary information and data for high-performance computing. The realization of virtual things makes all kinds of stimuli generated by things in the computer-generated virtual world feed back to users as naturally as possible through various calculation and simulation technologies.
1. True ambiguity
The virtualization of objects mainly includes key technologies such as basic model construction, spatial tracking, sound localization, visual tracking, viewpoint perception, etc., which makes it possible to generate a realistic virtual world, detect user operations in the virtual environment and obtain operation data.
(1) basic model construction technology
The construction of basic model is the basis of applying computer technology to generate virtual world. It reconstructs real-world objects in the corresponding three-dimensional virtual world and saves some physical properties according to the system requirements.
Firstly, the geometric model of the object should be established, and its spatial position and the attributes of geometric elements should be determined. For example, establish a three-dimensional geometric model of a product or building through cad/cam or two-dimensional drawings; Build a large-scale virtual battlefield through gis data and satellite, remote sensing or aerial photos.
In order to enhance the realism of virtual environment, the modeling of physical characteristics and behavior rules should show the physical characteristics of objects, such as mass, momentum, materials, etc., and follow certain laws of motion and dynamics in virtual environment.
When it is difficult for geometric models and physical models to accurately describe some special objects or phenomena existing in the real world, some special model construction methods can be adopted according to specific needs. For example, meteorological data can be modeled to generate meteorological conditions (cloudy, sunny, rainy, foggy) of the virtual environment.
(2) Space tracking technology
The spatial tracking of virtual environment mainly determines the position and direction of the user's head, hands, body or other operating objects in the three-dimensional virtual environment through the spatial sensors on interactive devices such as helmet display, data gloves and data suits.
Tracking system usually consists of transmitter, receiver and electronic components. At present, there are several tracking systems, such as electromagnetic, mechanical, optical and ultrasonic.
Data glove is a commonly used human-computer interaction device in vr system, which can measure the position and shape of the hand to realize the virtual hand in the environment and its manipulation of virtual objects. Cyber glove determines the position and direction of hands and joints through bending and torsion sensors on fingers and bending and radian sensors on palms.
(3) Sound tracking technology
It is an important part of virtual reality to track the sound in virtual environment by using the time difference, phase difference and sound pressure difference of different sound sources. Acoustic time-of-flight measurement and phase coherence measurement are two basic algorithms to realize sound position tracking. The acoustic time-of-flight method can show good accuracy and consistency in a small working range. With the expansion of the working range, the data transmission rate of acoustic time-of-flight method decreases, which is vulnerable to the pulse interference of pseudo-sound. The phase coherence method is not susceptible to noise interference in nature, and allows the existence of redundant data to be filtered without causing stagnation. However, the phase coherence method can not directly measure the distance, but only the change of position, which is easily disturbed by accumulated errors.
Sound tracking usually includes several transmitters, receivers and control units. You can connect the helmet display, data suit, data gloves and other devices.
(4) Visual tracking and viewpoint perception technology.
The visual tracking technology of object blur is to calculate the position and direction of the tracked object by using the projection of the camera to the x-y plane array, and the ambient light or tracking light on the image projection plane at different times and positions. The realization of visual tracking must consider the compromise between accuracy and working range. The design of multi-transmitter and multi-sensor can improve the accuracy of visual tracking, but it will make the system complicated and expensive.
Viewpoint perception must be combined with display technology, and various positioning methods (eye patch positioning, helmet display, remote viewing technology and eye muscle-based perception technology) can be used to determine the user's line of sight at a certain moment. For example, by integrating viewpoint detection and sensing technology into helmet display system, pilots can manipulate virtual switches or conduct flight control in some extraordinary times just by "looking".
2. Virtual reality
The key technology to ensure users to obtain sensory cognition such as vision, hearing, strength and touch in virtual environment is the main research content of virtual reality.
(1) visual perception
Most objects or phenomena with certain shapes in virtual environment can make users have a strong sense of reality in many ways. Crt display, large screen projection, multi-directional electronic wall, stereo glasses and hmd are common display devices in vr system. Different helmet monitors have different display technologies. According to the way of providing optical images, helmet display devices can be divided into projection type and direct-view type.
Stereo display technology can enhance the realism of virtual environment, and enable users to see two plane images with parallax with their left and right eyes, and synthesize them in their brains to produce stereoscopic vision perception. Helmet display and stereoscopic glasses are two common stereoscopic display devices. At present, the stereoscopic display technology based on laser holographic calculation and the display technology of directly imaging on retina with laser beam are being studied.
(2) Hearing
Hearing is second only to vision, and the sound effect of virtual environment can make up for the deficiency of visual effect and enhance the fidelity of the environment.
The three-dimensional sound perceived by the user helps the user to locate the sound in the operation. The localization of traditional sound model is based on the time difference itd between the sound source and the listener's ears and the pressure difference iid between the sound source and the left and right ears, but it can't explain the monaural localization. Modern sound model focuses on the head-related transfer function hrtf to describe the propagation process of sound from sound source to external auditory canal, and can support monaural localization. Hrtf mainly uses filtering method to simulate head effect, auricle effect and head masking effect. Nasa air force research center once placed a small microphone in the artificial ear canal to record the impulse responses of many different sound sources to the head, and then generated a sense of location in the virtual environment according to hrtf and impulse results.
(3) force perception and touch
A key factor that can make participants feel "immersed" is whether the user can feel the reaction of the virtual object while manipulating it, so as to produce touch and force perception. For example, if you pull the gear lever of the virtual driving system by hand, your hand can feel the vibration and tightness of the gear lever.
Force sensing mainly means that the computer dampens the movement of fingers through force feedback gloves and force feedback joysticks, so that users can feel the direction and magnitude of force. Because people's sense of force is very sensitive, ordinary precision devices can't meet the requirements at all, and it is quite difficult and expensive to develop high-precision force feedback devices, which is one of the difficult problems people face.
Without tactile feedback, when a user touches an object in the virtual world, it is easy to make his hand pass through the object. An effective way to solve this problem is to add tactile feedback to the user's interactive device. Tactile feedback is mainly based on vision, barometric sense, vibration touch, electronic touch and neuromuscular simulation. Electronic tactile feedback that feeds back variable electrical pulses to the skin and neuromuscular analog feedback that directly stimulates the cortex are not safe. Relatively speaking, barometric pressure and vibration tactile feedback are relatively safe tactile feedback methods.
3. High performance computing technology
Virtual reality is a modern high-tech with computer technology as its core, and high-performance computing technology is the key to directly affect the system performance. High-performance computing and processing technology has the characteristics of fast computing speed, strong processing ability, large storage capacity and strong networking, and mainly includes the following research contents:
(1) data conversion and data preprocessing of fuzzy and materialized objects; (2) Real-time realistic graphic image generation and display technology; (3) Various technologies of sound synthesis and sound spatialization; (4) Multi-dimensional information data fusion, data conversion, data compression, data standardization and database generation; (5) Pattern recognition. For example, command recognition, voice recognition, and the detection, synthesis and recognition of gestures and human facial expression information; (6) Research on advanced computing model. Such as expert system, self-organizing neural network and genetic algorithm. (7) Distributed and parallel computing, and high-speed, large-scale remote network technology.
4. Distributed virtual reality
The research goal of distributed virtual reality is to establish a distributed virtual environment for multiple users to participate in different places at the same time. Users in different geographical locations are like entering a real world, not limited by physical time and space, communicating, learning, discussing, training and entertaining through gestures, sounds or words, and even cooperating to complete the same complex product design or the same difficult task practice.
There are two camps in the research of distributed virtual reality. One is distributed virtual reality on the Internet, such as remote virtual shopping based on vrml standard. The other is a high-speed private network invested by the military, such as dsi, a US military defense simulation internet using atm technology.
Domain that should be used
The emergence and development of vr technology provides a new way to solve and deal with various problems that require huge capital and manpower investment or have to bear the danger of casualties. At present, the application of vr technology mainly focuses on the following aspects:
1. product design and performance evaluation
The design of Boeing 777 is a typical application example of virtual prototype, which consists of 3 million parts, all of which are designed in a virtual environment composed of hundreds of workstations.
From 65438 to 0996, UC Berkeley realized the real-time roaming of soda hall in the new building on sgi workstation. The Virtual Reality and Visualization New Technology Laboratory of Beihang University has also completed the development of Changhengyuan and its interior decoration, virtual Beihang University and other roaming systems. At present, a roaming system of Mount Everest and its surrounding environment is being built for the National Science and Technology Museum.
2. Education and entertainment
Applying vr technology to education allows students to visit the seabed, travel in space, observe historical castles, and even go deep into atoms to observe the trajectory of electrons. The distributed virtual library breaks through the limitation of physical time and space and makes effective use of resources. The distributed virtual library based on Internet has a bright future.
Vr technology is widely used in the entertainment industry. The first large-scale vr entertainment system "battletech" connects all "cockpit" simulators for group confrontation. Three-dimensional realistic scenes, joysticks, throttles, brakes, and shaking during impact give users strong sensory stimulation.
3. Training in a difficult and dangerous environment
Vr system, which serves the training of medical surgery, uses ct or mri data to reconstruct the geometric model of human body or an organ in the computer and endow it with certain physical characteristics (such as density, toughness, tissue proportion, etc.). ), and with the help of high-precision interactive tools such as manipulator or data glove, the surgical process is simulated in the computer, so as to achieve the purpose of training and research.
Nasa and esa (European Space Agency) in the United States have successfully applied vr technology to the space activities of spacecraft, the free operation of space station and the maintenance of Hubble space.
4. Distributed virtual battlefield environment
Military field is the earliest research and application field of vr technology. The earliest distributed virtual battlefield environment should be the simnet research plan made by darpa and the US Army in 1983. Starting from 1994, darpa and usacom of the United States jointly carried out the research on stow, forming a military exercise environment covering 500×750km2, including the participation of 3,700 simulation entities.
Since China 1996, dvenet supported by the National 863 Program is a basic information platform of distributed virtual environment jointly developed by Beihang University, Zhejiang University, National University of Defense Technology, Academy of Armored Forces Engineering, Institute of Surveying and Mapping of PLA and Software Institute of Chinese Academy of Sciences. In the distributed virtual battlefield environment based on dvenet, a number of real simulators and virtual simulators distributed in different regions are combined to simulate the cooperative confrontation tactics in different places.
Abstract: Virtual reality is a research field with many unsolved problems and emerging new problems, and it is also a high-tech field full of vitality and great application prospects. We should be able to make a difference in this field.