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Battlefield environment is the spatial basis of all military operations, and battlefield environment simulation is currently a hot topic in the field of military combat simulation. This article discusses the composition of the 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 practical characteristics, and the command art and combat capabilities of commanders and soldiers need to be in a certain war environment get exercise and improvement. In war years, this ability can be accumulated through real war practice, but this kind of practice cannot be repeated or tested, and the price is very high. Therefore, even in war years, non-wartime training has become the key to victory, and the standard guiding training is war practice itself. In peacetime, military exercises are a common training method, and the ability to control war practice is accumulated and improved through experiments in various combat styles. Due to the lack of actual combat testing, each training style also determines the style of future combat.

Since the emergence of war in human history, people’s research on military training has been aimed at learning and exploring the laws of war, and the special research of "combat simulation" has gradually formed in the field of training. theme. Combat simulation is the simulation of the essential laws of war, including the laws of war and the laws of war guidance [1]. The first point is to create a training environment close to actual combat so that all types of trainees can practice in this environment. Get the right training[2].

The battlefield environment is the space for combat activities of both hostile parties. In modern combat simulation, to create a training environment close to actual combat, we must first establish a digital training environment that meets the needs of specific combat training subjects based on simulation principles. The battlefield environment is called Battlefield Environment Simulation. The content of battlefield environment simulation includes battlefield perception. Virtual reality is a very effective simulation technology that emerged in the late 1990s. This article will focus on how to use virtual reality technology to realize battlefield environment simulation.

1． Overview of battlefield environment simulation

1. 1 The composition of the battlefield environment

The battlefield environment refers to the objective environment in the combat space other than personnel and weapons and equipment. Analyzing the objective factors involved in 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 multi-dimensional and interactive. The meaning of multidimensionality is: ① The battlefield environment is composed of multiple objective environments with their own changing laws. The above four environments belong to different subject areas; ② The spatial form of these objective environments evolves with the combat process. The meaning of interactivity is: the above-mentioned environments influence each other. Among them, the terrain environment is the physical support of other environments and the basis for spatial positioning and loading of various combat information. As shown in Figure 1, in the battlefield environment, the meteorological environment and the geographical environment influence each other. The meteorological environment has geographical characteristics, such as different geographical locations have tropical, subtropical and other meteorological characteristics, and the meteorological environment will affect the geographical environment, such as flowing water eroding the landforms. , the formation of glacial landforms, rainy and sunny days have an impact on the ground soil quality, which in turn affects the marching speed; the geographical environment and meteorological environment have a major impact on the formation of the electromagnetic environment, which not only stipulates the distribution of electronic facilities, but also determines the transmission range of electromagnetic waves and the degree of meteorological interference; the formation of a battlefield nuclear environment is related to the geographical location of nuclear facilities and their surrounding environment. The formation and development of nuclear contaminated areas are closely related to the geographical environment and meteorological environment.

1.2 Battlefield environment simulation and its description method

Battlefield environment simulation refers to the use of simulation technology to describe the battlefield environment. Simulation is the study of an existing or designed system through experiments on system models. Computer simulation (also called mathematical simulation) refers to the use of computers to test real systems or systems under design using system models to achieve the purpose of analyzing, researching and designing the system [3]. Here, a system refers to an organic whole of a set of interconnected elements with specific functions to achieve a certain purpose. The simulation of a system involves three elements: system, system model, and computer, and the basic activities connecting these three elements are: model establishment, simulation model establishment, and simulation experiment [4] (as shown in Figure 2).

If the battlefield environment is viewed as a battlefield space system, its specific function is to constitute the space carrier and physical conditions of the battlefield. The relationship between various environments in the battlefield environment constitutes the organic whole of this space carrier. To use computers to simulate battlefield environments, we first need to digitize the battlefield environment, that is, establish a battlefield environment model. Digital maps are a typical battlefield environment model. This model is versatile, but often cannot meet some special needs. For example, modern combat simulation still follows the war game deduction method, and needs to process terrain environment data at a certain resolution into data stored in a grid, and these data are also It changes dynamically as the combat process unfolds.

This process of processing the battlefield environment model into a model suitable for combat simulation is the secondary modeling of the battlefield environment (simulation modeling). The battlefield environment model processed by 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 a certain degree of accuracy, which requires testing the model through simulation experiments (model verification).

Based on the use of battlefield environment simulation in combat simulation, it can be divided into two description methods: data simulation and perception simulation. Data simulation is mainly used for simulated confrontation and combat assessment. At this time, the battlefield environment data is provided for the computer to "understand" the battlefield. It is better to convert the basic battlefield environment data into a battlefield environment model that the computer can recognize. The process is called "battlefield". Modeling”. Perceptual simulation is mainly aimed at command operations and training simulation, that is, the battlefield environment is displayed through battlefield visuals, sound effects and other elements. The commander can perceive the battlefield environment through a certain operating interface to assist on-site survey, grasp the situation and assist decision-making. , the result of this "battlefield perception" is used by the human brain to understand the battlefield. The data simulation and perception simulation of the battlefield environment are both based on the digital battlefield environment. In practical applications, these two simulation description methods interact with each other. The data simulation changed according to the model drive is presented to the trainees through perception, and Participants can change the results of data simulation through human-computer interaction. Figure 3 illustrates the relationship between the two description methods of battlefield environment simulation. Due to space limitations, this article only discusses the content and key technologies of perception simulation of the battlefield environment.

1.3 The main content of battlefield environment perception simulation

The purpose of perception simulation is to fully train the command and decision-making abilities of trainees by visually displaying the battlefield environment. Its content includes the simulation of multiple sensory channels such as vision, hearing, and touch in the battlefield environment. Visual simulation, often called "battlefield visualization", is a major form of perceptual simulation, which combines visible (such as terrain, features) and invisible (such as electromagnetic fields, tidal flow fields) elements in the battlefield environment into three-dimensional , three-dimensional or two-dimensional graphics and images. Auditory simulation refers to creating a battlefield atmosphere by simulating the sounds (sound effects, volume and phonemes) of each combat unit on the battlefield. Tactile simulation refers to the communication between people and the environment through the operation of human-computer interaction equipment. This is an important means to create a sense of presence for participants. This technology that achieves on-the-spot feeling through the simulation of multi-sensory channels is virtual reality technology. Compared with the traditional way of understanding the battlefield through maps, physical sandboxes or video materials, in such a system, trainees are transformed from bystanders into participants and can actively explore in a realistic environment. , thereby greatly improving the efficiency of battlefield recognition.

2. Virtual reality and battlefield environment perception simulation

2.1 Application of virtual battlefield environment in perception simulation

The term virtual reality (VR) Born in the late 1980s, it refers to a computer-generated environment with a sense of presence [5][6]. The technology to realize this environment is called virtual reality technology. The military is a sponsor and early user of this technology, primarily for military training. In 1988, NASA and the U.S. Department of Defense jointly supported the development of a virtual interface environment workstation VIEW (Virtual Interface Environment Workstation). The workstation consisted of an HP-9000 computer, a pair of data gloves, an LCD helmet-mounted display and a set of It consists of a speech recognition system, from which users can see three-dimensional images, hear three-dimensional sounds, issue verbal commands, and reach out to grab computer-generated virtual objects. This is the world's first virtual reality system [7]. Since then, virtual reality technology and its products have developed rapidly and formed an industry. According to statistics from a special report by Jane's Information Group [8], by 2000, the production of virtual reality products related to training simulations There are more than 800 companies, and its market will grow from US$40 billion in 2000 to US$65 billion in 2010.

Virtual reality products are widely used in the field of combat simulation, and most of them involve battlefield environment simulation. The purpose of using virtual reality technology to realize battlefield environment simulation is to form a multi-dimensional, perceptible, measurable, and realistic virtual battlefield environment, thereby improving the trainees' cognitive efficiency of the battlefield environment. Mainly used for simulation confrontation, guidance monitoring, equipment operation, staff operation training, etc. The virtual battlefield environment can provide a simulation environment similar to the actual exercise area for computer combat deductions, semi-real-force exercises, and real-force exercises. It can also construct a typical training environment for specific training subjects (which does not exist in reality). With the help of the virtual battlefield environment, the commander's command and decision-making ability, the staff's business ability, and the equipment operator's operational ability can be trained. For example, SIMNET, a network-based distributed tank training simulation system developed by the US military since 1984, has included 10 regional combat environments in the United States and Europe within the system. By 1990, 200 armored vehicles had been enabled to participate in interactive simulation exercises under unified command in remote locations.

Each simulator uses an American M1 main battle tank as a unit to provide accurate terrain relief, vegetation, roads, buildings, bridges and other information in the combat area. Tankers can see a real-time computer-generated battlefield environment and images of other tanks in the simulator. In 1991, the United States provided a battlefield environment simulation system for the M1A1 main battle tank for the implementation of the "East Longitude 73" plan in the Gulf Campaign. The desert environment of Iraq was displayed in front of the combatants on three large screens for an immersive experience. The battlefield research of the environment laid a key foundation for the final victory. The Stinger Missile Trainer (VST) completed by the Netherlands in 1992 is a masterpiece of virtual reality technology used in individual weapon simulation equipment. It forms a spatial dynamic three-dimensional scene in the helmet; the scene changes accordingly with the operator's head movements. In order to train the operator's maneuverability and aiming ability to deal with enemy aircraft, the pre-prepared VCD disk provides corresponding sound effects for various combat environments [9]. In 1997, Lockheed Martin Vought developed a practical exercise system TOPSCENE (Tactical Operations Live) for the U.S. Naval Aviation Training Systems Program Office. This is an equipment that comprehensively uses military surveying and mapping results and virtual reality technology. It is widely used in the Navy, Marine Corps, Army and Air Force, and has been equipped with more than 100 sets. The system uses an SGI graphics workstation (the highest configuration is ONYX2, 4 R1000CPUs) to process image data. Under high configuration, it can produce 30 frames per second of detailed and realistic high-resolution battlefield images. The system can simulate various terrain elements, different meteorological conditions, and can also simulate the night battle process with night vision devices, infrared displays or synthetic aperture radar display effects.

2.2 The basic composition of the virtual battlefield environment system

The virtual battlefield environment system consists of three parts: 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, etc.; the database system mainly includes battlefield map database, three-dimensional environment model database, weapons and equipment Database, environmental texture image database, application topic database, etc.; hardware systems mainly include computers, audio and video processing systems, perception systems (display equipment, stereoscopic observation devices, human-machine control devices), etc. According to the application requirements of the virtual battlefield environment, the above three parts can be combined in different ways to form different application systems.

As far as military applications are concerned, the virtual battlefield environment mainly has two application modes: multi-player enjoyment and single-soldier immersion. Correspondingly, the virtual battlefield environment system has multi-player enjoyment. The main difference lies in the way of display and observation of stereoscopic images and the way of controlling the scene.

(1) Multi-person enjoyment. In combat command and most combat simulations and training, commanders and staff often need to discuss combat plans and evaluate combat effects around the same battlefield environment. In order to meet the needs of multi-person enjoyment, most of the current virtual battlefield environment systems use large-screen projection display and observation through stereoscopic glasses (liquid crystal or polarized light) to achieve visual enjoyment, and use joysticks to achieve visual enjoyment. Or input devices such as mouse and keyboard to control the viewpoint. The advantage is that users (a few to dozens of people) in the same space can observe the same scene at the same time, and the system hardware is cheap. The disadvantage is that the operation of the scene can only be completed by one person, and when the image projected on the large screen cannot fill the observer's field of vision, the sense of immersion will be weakened.

(2) Individual soldier immersion. In the application of individual soldiers' operational training of technical and tactical weapons and equipment, what needs to be emphasized is the relationship between the individual trainee, the weapons and equipment, and the environment in which they are located. For this reason, helmet-mounted displays (HMDs) are often used as stereoscopic display, stereoscopic observation and head positioning and tracking devices, and data gloves or body position trackers are used to complete positioning, selection and other operations. The use of these devices can give trainees a strong sense of presence, thereby achieving good training effects. However, its equipment is very expensive and difficult to promote and use. Moreover, because the sensing device is not very accurate and the computer has limited computing power for scenes with large amounts of data, it often causes pathological reactions of the senses.

3. Several key technologies for constructing a virtual battlefield environment

As a virtual reality system, it is generally believed that it needs to have three basic characteristics - interaction, immersion and imagination ( Imagination) [10], but depending on the actual use, the embodiment of these "3I" characteristics is also focused. As far as the most enjoyable virtual battlefield environment system is concerned, the focus is on interactivity; for the immersive virtual battlefield environment system, the emphasis is on its immersive characteristics (accessibility); no matter what kind of application, imagination is the key is indispensable.

3.1 Key technologies for realizing “interaction”

Interaction characteristics refer to the system’s ability to respond to human-computer interaction. The standard for measuring this ability is system processing and display The refresh rate of the environment image (frames/second). The higher the refresh rate, the faster the system can respond to interaction. When the interaction response reaches real-time, it will visually appear as the scene changes continuously and smoothly with the interaction process. When there is a significant delay in the interactive response, it will visually appear as stagnation and jittering changes in the scene.

Obviously, in addition to the performance of the system hardware for scene data processing and display, factors that affect interaction capabilities are also related to the amount of data in the scene and the interactive control software. Therefore, when constructing a virtual battlefield environment system, the performance of the equipment and the actual equipment capabilities of the user must be fully considered. The key to software system development lies in the organization and management of scene data.

In battlefield environment simulation applications, the scene data involved in visualization processing includes three-dimensional terrain models, three-dimensional feature models and surface textures of terrain features (if the composition of the comprehensive battlefield environment is taken into account, weapons should also be included Equipment models and their textures, as well as pyrotechnics special effects, sound effects and other data), the amount of data is very large. In order to realize real-time interactive display of large-scale landscapes, 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 to a minimum while ensuring the details of scene display to ensure interactive response. efficiency. Our practice shows that organizing and scheduling scene data according to the laws of human visual cognition is an effective method. This rule is: when looking at an objective object from a fixed viewpoint, the closer to the center of vision, the clearer the image on the retina, and the further away, the blurr the image; when observing an objective object from different viewing distances, the closer to the object, the clearer the image. The more details you see, the richer the objects you see. Following the above rules, the organization and scheduling of scene data actually boils down to the organization of the scene detail level and the scheduling of data at each level related to the viewpoint [11].

(1) Organization of scene detail level: The details of the scene include the details of the scene model and the details of the scene texture. The details of the scene model refer to the details expressed by the scene volume form, 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 used to build the model. For battlefield environment simulation applications that use vector map data as the main data source, the original scale of the digital map determines the highest detail described by the scene model, that is, the larger the scale, the The richer the details. The highest detail of the scene texture depends on the data source of the texture image. When a data map is used as the data source for simulating 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 classified the ground features will be. The more detailed it is, the richer the details of the surface that the simulation image can describe; when remote sensing images are used as the surface texture, the image resolution determines the details that the surface elements can show.

In order to achieve the effect of scene expression with richer details the closer the viewpoint, the scene model and texture data need to be divided into multiple levels of detail and organized according to detail sequences.

(2) Scheduling of hierarchical data related to viewpoints: In the same scene, different detailed models and texture data are scheduled according to the principle of detailed peripheral outline of the visual center, which is also to maintain interaction and vision. An effective method to reduce the amount of landscape data involved in calculation.

It should be noted that texture details can visually make up for the lack of model details, that is, superimposing textures with more details on a more general model skeleton, which improves interaction efficiency without reducing the display effect. An effective strategy.

3.2 Key technologies to achieve "immersion"

The immersion feature refers to the sound and image effects of the system that can make trainees feel like they are in a virtual environment. For most applications, creating a three-dimensional visual effect is the key to achieving "immersion". That is, based on the principle of human binocular stereo vision, with the help of certain equipment, the observer can have a strong physiological impact on the scene being observed. Three-dimensional feeling. Since in the virtual reality system, the scene is generated by a computer (not shot on site), in order to achieve the three-dimensional effect, it is necessary to humanize the image generation, display and observation aspects, so this technology is also called " Artificial stereoscopic vision technology”[5][12].

(1) Generation of stereoscopic images. It is based on the horizontal parallax of physiological stereoscopic vision to generate scene images with the left and right eyes as the viewpoints of the same scene, that is, forming an image pair. The parallax of the image pair is the only factor that causes the physiological three-dimensional feeling and determines the depth effect of the scene. Regarding the types of parallax and their corresponding visual effects, please refer to reference [12].

(2) Display and observation of stereoscopic images. The display mode and the observation mode are closely related. Which mode to choose depends on the needs of the actual application. The above content describes the two display and observation modes in battlefield environment simulation applications. These two methods are also the mainstream in the market. However, since these two methods require part of the observation device to be worn on the observer's head, and the observation effect is not ideal (for example, LCD glasses will increase flicker and reduce scene brightness, The display resolution of LCD helmets is low, CRT helmets are heavy, etc.), so many users would rather choose the three-dimensional observation method, that is, watch the monocular scene video generated by the computer directly on the monitor or projection screen, and use the light, shadow and form in the scene to As clues, through the observer's mental processing, a three-dimensional feeling (actually an illusion) is produced. Recently, Germany's Dresden 3D Co., Ltd. launched a three-dimensional LCD display that allows observers to see three-dimensional images without wearing any observation devices. The display is equipped with an eye-tracking camera that captures the position of the observer's eyes, thereby controlling an optical mask installed in front of the LCD screen to shift the left and right eye images in the direction of the left and right eyes respectively. Obviously, this monitor is not suitable for multi-person sharing.

In battlefield environment simulation applications, environmental sounds are mainly sounds such as engine roars, gunfire, and ammunition explosions emitted by weapons and equipment during combat. The characteristics of these sounds are that they have exact spatial positions and sound effects. Through software that can describe spatial sounds (such as Direct 3D), the sound positioning information can be transmitted to the user through the sound system. Loud battlefield audio can create a vivid and realistic battlefield atmosphere.

3.3 Reflecting several aspects of "imagination"

Taking "imagination" as a basic feature of virtual reality systems shows the importance of creative image thinking ability in building virtual reality systems. importance. Superb creativity can not only shock the viewer's soul, but also guide them to achieve the purpose of exploration. For the creation of a virtual battlefield environment, this imagination is reflected in the conception of the human-machine interface, the conception of scene expression, and whether to provide means to recreate the battlefield environment.

(1) Concept of human-computer interface. “The most difficult part of VR is to make the user’s sense of information certain.” This is Bill Gates’s understanding of the highest state that a virtual environment should reach [13]. In order for users to "enter" the scene generated by the system and be convinced of it, a good human-computer interface is required. The traditional human-computer interface allows users to observe and operate application software through a "window". In a virtual environment, such a window will block the user from 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 the virtual environment has become the focus of imagination.

(2) Concept of scene description. In fact, it refers to the design of virtual scenes. Whether the appearance of the virtual battlefield environment is realistic or not mainly depends on the appearance design of the scene. When using vector map data to generate the surface texture of a scene, the concept of scene description involves the design of the representation method of each element (using geometric symbols or simulated images), the design of the surface and surface noise effects of each element, and the design of different landform types. The design of the color layer table, the design of the representation method of weapons and equipment and other combat units in the battlefield environment, the design of the representation method of combat intention and situation, etc.

(3) Provide tools to realize ideas. In different military applications, users have different requirements for the representation of virtual battlefield environments. For example, for flight simulation training, trainees hope to use aerial images as surface textures to make the scene visually closer to the actual terrain. environment. However, for combat command training, trainees prefer that the classification and grading information on the map (symbolic representation method) can be expressed in the scene for analysis and decision-making, which requires multiple expression methods for users in the system. In addition, for research on tactics, users sometimes need to construct a typical battlefield environment, which also requires providing users with tools to realize their ideas.

4． Application examples

Since 1995, the Battlefield Environment Simulation Engineering Laboratory of the School of Surveying and Mapping of the University of Information Engineering of the People's Liberation Army has done a lot of research work on the theme of virtual battlefield environment, and has achieved the "Terrain Environment Simulation System" as the theme. represent the results. This system is a practical system that uses virtual reality technology and the support of military surveying and mapping databases to realize battlefield environment simulation. It mainly simulates the terrain environment of the combat area, and can provide various two-dimensional electronic maps, three-dimensional landscapes and Geographic information.

This system has initially possessed the basic characteristics of virtual reality ("enterable" and "interactive"), and the following key technical issues have been solved during the development process:

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

2. The interface hardware with LCD stereoscopic glasses has been developed, so that in a computer and workstation environment, lower-priced stereoscopic glasses can be used to achieve a "feeling of entry" stereoscopic effect.

3． It solves the interface problems between terrain models and other commercial 3D software, as well as the placement of technical and tactical weapons in the 3D terrain environment (Figure 5).

At present, this system has been widely used in the entire military and has also been used in national economic construction. For example, this system was used to simulate the water inundation process in the Three Gorges Reservoir area for the Three Gorges Immigration Bureau (such as Figure 6).

5. Conclusion

Battlefield environment simulation is a high-tech technology produced in response to the needs of digital battlefield construction, and its application fields are very wide. This article only discusses the application of virtual reality technology in battlefield environment perception simulation from the application field of combat simulation. In fact, this technology is also used in combat command, weapons testing, diplomatic negotiations, disaster prediction and other aspects in the military. As virtual reality technology becomes more mature and practical, we believe that in the near future, it will become an important technical means to improve the combat effectiveness of the military.