What is the significance, present situation and application prospect of battlefield simulation research?

Simulation of Battlefield Environment Based on Virtual Reality Technology

Abstract: Battlefield environment is the spatial basis of all military actions, and battlefield environment simulation is a hot spot in the field of military combat simulation at present. This paper discusses the composition of battlefield environment and the main contents of battlefield environment simulation, focusing on the application and key technologies of virtual reality technology in battlefield environment perception simulation.

Keywords: battlefield environment, battlefield environment simulation, virtual reality

War has strong actual combat characteristics, and commanders' command art and combat ability need to be tempered and improved in a certain war environment. In wartime, this ability can be accumulated through real war practice, but this practice is unrepeatable and untestable, and its cost is very high. Therefore, even in wartime, non-wartime training has become the key to success, and the standard for guiding training is the war practice itself. In peacetime, military exercise is a common training method. Through experiments of various combat styles, the ability to control war practice is accumulated and improved. Due to the lack of actual combat test, each training style also stipulates the style of future operations.

Since the emergence of war in human history, people's research on military training has been aimed at learning and discussing the laws of war, and gradually formed a special research theme of "combat simulation" in the training field. Combat simulation is the simulation of the essential laws of war, including the laws of war and the laws of war guidance [1], and its primary point is to create a training environment close to actual combat, so that all kinds of trainees can get proper training in this environment [2].

Battlefield environment is the space where hostile parties fight. In modern combat simulation, to create a training environment close to actual combat, we must first establish a digital battlefield environment that meets the needs of specific combat training subjects according to the simulation principle, which is battlefield environment simulation. Battlefield environment simulation, including battlefield-aware virtual reality, is a very effective simulation technology in the late 1990s. This paper will focus on how to use virtual reality technology to realize battlefield environment simulation.

1. Overview of battlefield environment simulation

1. 1 composition of battlefield environment

Battlefield environment refers to the objective environment except personnel and weapons and equipment in combat space. Judging from the objective factors involved in the war, the battlefield environment should include the battlefield geographical environment, meteorological environment, electromagnetic environment and nuclear environment. Perhaps, with the formation of network information warfare, the battlefield network environment will also become an important part of the battlefield environment.

The battlefield environment is multidimensional and interactive. The multi-dimensional significance is as follows: ① The battlefield environment is composed of multiple objective environments, each of which has its own changing law, and the above four environments belong to different disciplines; (2) The spatial form of these objective environments evolves with the battle process. The meaning of interactivity is that the above-mentioned environments influence each other, in which the terrain environment is the physical support of other environments and the basis for spatial positioning and loading various operational information. As shown in figure 1, in the battlefield environment, meteorological environment and geographical environment interact with each other, and the meteorological environment has geographical characteristics, such as tropical and subtropical meteorological characteristics in different geographical locations, which will affect the geographical environment, such as the formation of flowing water erosion landforms and glacier landforms, and rainy and sunny days will affect the ground soil quality, thus affecting the marching speed; Geographical environment and meteorological environment have great influence on the formation of electromagnetic environment, which not only stipulates the distribution of electronic facilities, but also determines the spread range of electromagnetic waves and the degree of meteorological interference. The formation of the battlefield nuclearization environment is related to the geographical location of nuclear facilities and their surrounding environment, and the formation and development of nuclear pollution areas are closely related to the geographical environment and meteorological environment.

1.2 battlefield environment simulation and its description

Battlefield environment simulation refers to using simulation technology to describe the battlefield environment. Simulation is to study an existing or designed system through the experiment of system model. Computer simulation (also known as mathematical simulation) refers to the experiment on the real system or the system being designed with the help of computers, so as to achieve the purpose of analyzing, researching and designing the system [3]. Here, a system refers to an organic whole of several interrelated elements with specific functions in order to achieve a certain purpose. The simulation of a system involves three elements: system, system model and computer. The basic activities related to these three elements are: model establishment, simulation model establishment and simulation experiment [4] (as shown in Figure 2).

If the battlefield environment is regarded as a battlefield space system, its specific function is to constitute the space carrier and physical conditions of the battlefield, and the relationship between various environments in the battlefield environment constitutes an organic whole of this space carrier. To realize battlefield environment simulation by computer, it is necessary to digitize the battlefield environment first, that is, to establish a battlefield environment model, and digital map is a typical battlefield environment model. This model is universal, but it often cannot meet some special requirements. For example, because modern combat simulation still uses the method of war chess deduction, it is necessary to process terrain and environment data into data and store them in the grid according to a certain resolution, and these data also change dynamically with the development of combat process. This process of processing the battlefield environment model into a model suitable for combat simulation is the secondary modeling (simulation modeling) of the battlefield environment. The battlefield environment model after secondary modeling can be used for computer combat simulation. In order to ensure the accuracy and reliability of combat simulation results, the battlefield environment model is required to have certain accuracy, which requires the model to be tested (verified) through simulation experiments.

According to the application of battlefield environment simulation in combat simulation, it can be divided into two description methods: data simulation and perceptual simulation. Data simulation is mainly used to simulate confrontation and operational evaluation. At this time, the battlefield environment data is provided to the computer to "know" the battlefield. The process of transforming basic battlefield environment data into battlefield environment model that can be recognized by computer is called "battlefield modeling". Perceptual simulation is mainly aimed at command operation and training simulation, that is, the battlefield environment is displayed through factors such as battlefield scenes and sound effects, and the commander perceives the battlefield environment through a certain operation interface, so as to achieve the purpose of assisting field investigation, grasping the situation and assisting decision-making. The result of this "battlefield perception" is to make people understand the battlefield. Both data simulation and perception simulation of battlefield environment are based on digital battlefield environment. In practical application, these two simulation descriptions are interactive. The data simulation according to the model changes is presented to the students through perception, and the students can change the results of the data simulation through human-computer interaction. Fig. 3 shows the relationship between two descriptions of battlefield environment simulation. Due to the limitation of space, this paper only discusses the content and key technologies of battlefield environment perception simulation.

1.3 Main contents of battlefield environment perception simulation

The purpose of perceptual simulation is to fully train participants' command and decision-making ability by displaying the battlefield environment intuitively. Its content includes the simulation of sensory channels such as vision, hearing and touch in battlefield environment. Visual simulation, also known as "battlefield visualization", is a main form of perceptual simulation, that is, the visible (such as terrain and objects) and invisible (such as electromagnetic field and tidal current field) elements in the battlefield environment are represented by three-dimensional, three-dimensional or two-dimensional graphic images. Auditory simulation refers to simulating the sound (sound effect, volume, phoneme) of each combat unit in the battlefield to create a battlefield atmosphere. Tactile simulation refers to the communication between human and environment through the operation of human-computer interaction equipment, which is an important means to make trainees feel on the spot. This technology to realize telepresence by simulating multi-sensory channels is virtual reality technology. Compared with the traditional cognitive way of understanding the battlefield through maps, physical sand tables or video materials, in such a system, participants are changed from bystanders to participants, and they can actively explore in a realistic environment, which greatly improves the efficiency of battlefield cognition.

2. Virtual reality and battlefield environment perception simulation

2. 1 application of virtual battlefield environment in perceptual simulation

Virtual reality (VR) was born in the late 1980s, which refers to a computer-generated environment with telepresence [5][6], and the technology to realize this environment is called virtual reality technology. The military department is the funder and the first user of this technology, which is mainly used for military training. 1988, NASA and the U.S. Department of Defense jointly developed the Virtual Interface Environment Workstation (View), which consists of an HP-9000 computer, a pair of data gloves, an LCD helmet display and a voice recognition system. Users can see three-dimensional images, hear three-dimensional sounds, give verbal commands, and reach out and grab computer-generated virtual objects. Since then, virtual reality technology and its products have developed rapidly and formed an industry. According to a special report of Jane's Information Group [8], by 2000, there will be more than 800 companies engaged in the production of virtual reality products related to training simulation, and their market will increase from 40 billion dollars in 2000 to 65 billion dollars in 20 10.

Virtual reality products are widely used in the field of combat simulation, mostly involving battlefield environment simulation. Using virtual reality technology to realize battlefield environment simulation, its purpose is to form a multi-dimensional, perceptible, measurable and realistic virtual battlefield environment, so as to improve the cognitive efficiency of participants on the battlefield environment. It is mainly used for simulated confrontation, guidance and monitoring, equipment operation and personnel training. The virtual battlefield environment can provide a simulation environment for computer warfare deduction, semi-real military exercises and real military exercises, and can also build a typical training environment for specific training subjects (which does not exist in reality). With the help of virtual battlefield environment, commanders' command and decision-making ability, professional ability of staff officers and operational ability of equipment operators can be trained. For example, SIMNET, a network-based distributed tank training simulation system developed by the US military from 1984, puts the 10 regional combat environment of the United States and Europe into the system. By 1990, 200 armored vehicles had been able to participate in interactive simulation drills under the unified command of different places. Each simulator takes the American M 1 main battle tank as the unit, and provides accurate information such as terrain fluctuation, vegetation, roads, buildings and bridges in the combat area. The tanker can see the battlefield environment and other computer-generated chariot images in real time in the simulator. 199 1 year, the United States provided a set of battlefield environment simulation system for M 1A 1 main battle tank to implement the "East longitude 73" plan of the Gulf campaign, showed the Iraqi desert environment to the combatants with three large screens, and conducted an immersive battlefield research, which laid a key foundation for the final victory. The Stinger Missile Trainer (VST) completed by Holland 1992 is a masterpiece of the application of virtual reality technology to individual weapon simulation equipment, which forms a spatial dynamic three-dimensional scene in the helmet. Use the operator's head movements to change the scene, so as to train the operator's maneuverability and aiming ability against enemy planes. VCD discs prepared in advance provide corresponding sound effects in various combat environments [9]. 1997, Lockheed? Martin Water Company has developed a set of actual combat exercise system TOPSCENE (Tactical Operation Reality) for the United States Naval Air Training System Project Office. The equipment is a comprehensive application of military surveying and mapping achievements and virtual reality technology, which is widely used in navy, marine corps, army and air force, and has been equipped with more than 100 sets. The system uses SGI graphics workstation (up to ONYX2 and four R1000 CPUs) to process image data. Under the high configuration, 30 high-resolution battlefield images with realistic details can be generated every second. The system can simulate various terrain elements and different meteorological conditions, and can also simulate the night battle process with night vision device, infrared display or synthetic aperture radar display effect.

2.2 the basic composition of the virtual battlefield environment system

The virtual battlefield environment system consists of software system, database system and hardware system. Its software system mainly includes battlefield environment modeling software, scene texture generation and processing software, stereo image generation software, observation and operation control software, analysis and application GIS software and so on. The database system mainly includes battlefield map database, three-dimensional environmental model database, weapons and equipment database, environmental texture image database, application thematic database and so on. The hardware system mainly includes computer, audio-visual processing system, perception system (display device, stereoscopic observation device, man-machine control device) and so on. According to the application requirements of virtual battlefield environment, the above three parts have different combinations, and then form different application systems.

As far as military applications are concerned, there are two main application modes of virtual battlefield environment: multi-person sharing and individual immersion. Accordingly, the virtual battlefield environment system consists of two types: multi-person sharing and individual immersion. The main differences are the display and observation methods of stereoscopic images and the control methods of scenes.

(1) Enjoy by many people * * *. In operational command and most operational simulation training, commanders and staff officers often need to discuss operational plans around the same battlefield environment and evaluate operational effects. In order to meet the needs of many people, most virtual battlefield environment systems realize visual enjoyment through large screen projection display and stereoscopic glasses (liquid crystal or polarized light), and control the viewpoint through input devices such as joystick, mouse and keyboard. Its advantage is that users in the same space (several to dozens) can observe the same scene at the same time, and the system hardware is cheap. Its disadvantage is that the operation of the scene can only be completed by one person, and when the large-screen projection image can not occupy the observer's field of vision, it will weaken the sense of presence.

(2) individual immersion. In the application of individual technical and tactical weapons and equipment operation training, it is necessary to emphasize the relationship between trainees and weapons and equipment and their environment. Therefore, HMD is often used as a device for stereoscopic display, stereoscopic observation and head positioning and tracking, and data gloves or attitude trackers are used to complete positioning and selection operations. Using these devices can make trainees have a strong sense of presence, and then achieve good training results. However, its equipment is very expensive and it is difficult to popularize and use. Moreover, because the sensing equipment is not very accurate, the computing power of the computer for large data scenes is limited, which often causes pathological reactions to the senses.

3. Some key technologies of constructing virtual battlefield environment.

As a virtual reality system, it is generally believed that it needs to have three basic features-interaction, immersion and imagination [10], but according to the actual use, it also emphasizes the embodiment of this "3I" feature. As far as the virtual battlefield environment system is concerned, it is the key to embody interactivity; For the immersive virtual battlefield environment system, the focus is on its immersion characteristics (accessibility); No matter what kind of application, imagination is indispensable.

3. 1 Key technologies to realize "interaction"

The interactive characteristic means that the system has the ability to respond to human-computer interaction, and the standard to measure this ability is the refresh rate (frame/second) at which the system processes and displays environmental images. The higher the refresh rate, the faster the system responds to the interaction. When the interactive response reaches real-time, the scene changes continuously and smoothly with the interactive process. When the interactive response has obvious delay, it is visually manifested as the stagnation and jitter change of the scene. Obviously, the factors that affect the interactive ability are not only the performance of the system hardware in processing and displaying scene data, but also the data volume of the scene and the interactive control software. Therefore, when building a virtual battlefield environment system, we should fully consider the performance of equipment and the actual equipment ability of users, and the key to software system development lies in the organization and management of scene data.

In the application of battlefield environment simulation, the scene data involved in visualization processing include three-dimensional terrain model, three-dimensional feature model and surface texture of terrain features (if the composition of comprehensive battlefield environment is considered, it should also include weapons and equipment model and its texture, fireworks special effects, sound effects and other data), and its data volume is very huge. In order to realize real-time interactive display of large amount of data, it is necessary to solve the problem of organization and management of scene data. The idea is to reduce the scene data involved in real-time processing as much as possible on the premise of ensuring the details of the scene display, so as to ensure the efficiency of interactive response. Practice shows that it is an effective method to organize and schedule scene data according to the laws of human visual cognition. The law is: when looking at an objective object from a fixed angle, the closer to the visual center, the clearer the image on the retina, and the more blurred it is; When observing an objective object from different sight distances, the closer to the object, the richer the details of the object. Following the above rules, the organization and scheduling of scene data actually comes down to the organization of scene details and the scheduling of data at all levels related to viewpoints [1 1].

(1) Organization of scene details: scene details include scene model details and scene texture details. The details of the scene model refer to the details expressed by the shape of the scene, and the details of the scene texture refer to the details expressed by the surface image of the scene. The highest detail of the scene model depends on the data source of the model. For the battlefield environment simulation application with vector map data as the main data source, the original scale of digital map determines the highest details described in the scene model, that is, the larger the scale, the richer the details. The highest detail of the scene texture depends on the data source of the texture image. When the data map is used as the data source to simulate the ground texture, the highest detail of the texture is also related to the scale of the digital map, that is, the larger the scale, the more detailed the classification of the ground features, and the richer the ground details can be described in the simulated image. When remote sensing image is used as surface texture, the resolution of the image determines the details that surface elements can display.

In order to achieve the scene performance effect that the closer the viewpoint is, the richer the details are. It is necessary to divide the scene model and texture data into multiple levels of details and organize them in the order of details.

(2) Scheduling of view-related hierarchical data: In the same scene, scheduling model and texture data with different details according to the principle of detailed outline of visual center is also an effective method to reduce the amount of landscape data involved in calculation and maintain interactive and visual effects.

It should be noted that texture details can make up for the lack of model details visually, that is, more detailed textures are superimposed on the rough model skeleton, which is an effective strategy to improve the interaction efficiency without reducing the display effect.

3.2 Key technologies to achieve "immersion"

Immersion feature means that the audio-visual effect of the system can make trainees feel in a virtual environment. For most applications, creating stereoscopic vision effect is the key to achieve "immersion", that is, according to the principle of human binocular stereoscopic vision, with the help of certain equipment, the observer will have a strong three-dimensional sense of the observed scene on the physiological level. Because in the virtual reality system, the scene is generated by computer (non-field shooting), and in order to achieve stereoscopic effect, it is necessary to deal with all aspects such as image generation, display and observation, so this technology is also called "artificial stereoscopic vision technology" [5][ 12].

(1) generation of stereoscopic images. According to the horizontal parallax of physiological stereoscopic vision, scene images with left and right eyes as viewpoints are generated for the same scene, that is, image pairs are formed. The parallax of the image pair is the only factor that causes the physiological stereoscopic impression, which determines the depth effect of the scene. Please refer to the reference [12] for the types of parallax and its corresponding visual effects.

(2) Display and observation of stereoscopic images. The display mode is closely related to the observation mode, and which mode to choose depends on the requirements of practical application. In the above content, two display and observation modes in battlefield environment simulation application are described. These two methods are also the mainstream in the market at present, but both of them need to put some observation devices on the head of the observer, and the observation effect is not ideal (for example, LCD glasses will increase flicker and reduce the brightness of the scene, LCD helmet display resolution is low, CRT helmet has deviation, etc.). ), so many users prefer to choose the way of stereoscopic observation, that is, watch the computer-generated monocular scene video directly on the display or projection screen, and follow the light, shadow and shape of the scene as clues. Recently, Germany Dresden 3D Co., Ltd. introduced a stereoscopic liquid crystal display, and observers can see stereoscopic images without wearing any observation equipment. The monitor is equipped with an eye tracking camera, which can capture the position of the observer's eyes, thus controlling an optical mask installed in front of the LCD screen to move the left and right eye images respectively. Obviously, this monitor is not suitable for many people to enjoy.

In the application of battlefield environment simulation, the environmental sound is mainly the sound of weapons and equipment in the course of combat, such as the roar of engines, the sound of artillery fire and the explosion of ammunition. These sounds are characterized by their precise spatial position and sound effect, and the positioning information of sounds can be transmitted to users through the sound system through software that can describe spatial sounds (such as Direct 3D). Noisy battlefield sounds can create a realistic battlefield atmosphere.

3.3 Several aspects of "imagination"

Taking "imagination" as a basic feature of virtual reality system shows the importance of creative thinking ability of images for constructing virtual reality system. Superb creativity can not only shock the hearts of the audience, but also guide them to achieve the purpose of exploration. For the creation of virtual battlefield environment, this imagination is embodied in the conception of man-machine interface, the conception of scene expression and whether to provide the means to recreate the battlefield environment.

(1) The concept of man-machine interface. "The hardest thing about VR is to make users feel convinced of information", which is Bill? Gates' Understanding of the Highest Realm of Virtual Environment [13]. In order to let users "enter" the scene generated by the system and be sure of it, a good man-machine interface is needed. The traditional man-machine interface is to let users observe and operate the application software through a "window". In the virtual environment, such a window will block the user in the position of a bystander and cannot "enter" the environment as a participant. Therefore, how to design a human-computer interaction interface that conforms to the characteristics of virtual environment has become the focus of imagination.

(2) The conception of scene description. Actually, it refers to the design of virtual scenes. Whether the appearance of virtual battlefield environment is realistic or not mainly depends on the appearance design of the scene. When using vector map data to generate scene surface texture, the idea of scene description involves the design of representation methods of each element (using geometric symbols or simulated images), the design of noise effect on the ground and the surface of each element, the design of color tables of different landform types, the design of representation methods of combat units such as weapons and equipment in battlefield environment, and the design of representation methods of combat intention and situation.

(3) Provide tools to realize ideas. In different military applications, users have different requirements for the performance of virtual battlefield environment. For example, in flight simulation training, students want to use aerial images as surface textures, which can make the scene visually closer to the actual terrain environment. For combat command training, students prefer to express the classified information on the map in the scene (symbolic representation) for analysis and decision-making, which requires providing users with various means of expression in the system. In addition, for tactical learning, users sometimes need to build a typical battlefield environment, which also needs to provide users with tools to realize their ideas.

4. Application example

Since 1995, the battlefield environment simulation engineering laboratory of Surveying and Mapping College of PLA Information Engineering University has done a lot of research work with the theme of virtual battlefield environment, and achieved the results represented by "terrain environment simulation system". This system is a practical system which uses virtual reality technology to realize battlefield environment simulation with the support of military surveying and mapping database. It mainly simulates the terrain environment of the combat area, and can provide 2D electronic maps, 3D landscapes and geographic information of various terrains for all levels (tactics, campaigns and strategies) and stages (planning, confrontation simulation and result evaluation) of combat simulation.

The system has initially possessed the basic characteristics of virtual reality ("accessibility" and "interactivity"), and solved the following key technical problems in the development process:

1. It solves the problems of rapid three-dimensional modeling, model simplification and real-time interaction of terrain environment in microcomputer environment.

2. The interface hardware with LCD stereoscopic glasses is developed, so that it can realize the stereoscopic effect with low-priced stereoscopic glasses under the environment of microcomputer and workstation.

3. Solve the interface problem between terrain model and other commercial 3D software, and the placement problem of technical and tactical weapons in 3D terrain environment (as shown in Figure 5).

At present, the system has been widely used in the whole army and national economic construction. For example, the system has been used to simulate the flood process in the Three Gorges reservoir area for the Three Gorges Immigration Bureau (Figure 6).

5. Conclusion

Battlefield environment simulation is a high-tech to meet the needs of digital battlefield construction, and its application field is very wide. This paper only discusses the application of virtual reality technology in battlefield environment perception simulation from the application field of combat simulation. In fact, this technology has also been used in many aspects such as combat command, weapon testing, diplomatic negotiation, disaster prediction and so on. With the maturity and practicality of virtual reality technology, we believe that it will become an important technical means to improve the combat effectiveness of the army in the near future.