Modeling virtual Reality technology - Dr. Cuidong Xu
Abstract: Virtual Reality technology, English Virtual Reality, referred to as VR. It is an ideal man-machine communication technology. This technology has three essential characteristics: immersion, interactivity and thinking. And virtual reality modeling technology is the core technology in virtual reality, this paper is based on 3DSMAX virtual reality modeling technology was studied, a brief introduction of 3DSMAX modeling tool, and finally the application of virtual reality modeling technology is explained.
Keywords: Virtual reality modeling technology, 3DSMAX, technical characteristics
1 concept of virtual reality technology
The most essential characteristics of virtual reality technology can be summarized by three I, namely Immersion, Interaction, Imagination. Immersion refers to the degree to which the user feels real in the virtual world. Interactivity refers to the degree to which users can manipulate objects in the virtual world and the degree to which they can get feedback from the virtual world. Virtual reality technology, as a new type of man-machine communication technology, is different from the traditional mode of keyboard and mouse. Using complex sensor equipment such as digital helmet and digital gloves, three-dimensional interaction technology, voice recognition and voice input technology have become important man-machine interaction means. And. In recent years, virtual reality technology has made rapid development, showing some new characteristics and development trends, mainly: virtual reality modeling technology, real-time THREE-DIMENSIONAL graphics generation and display technology, intelligent human-computer interaction equipment development, large network distributed virtual reality research.
2 virtual reality modeling technology
Virtual reality is a virtual digital space that simulates things in the real world. This is like a realistic digital model, so virtual reality modeling technology came into being. The authenticity of virtual reality technology is closely related to modeling technology, so the research of modeling technology has very important significance. According to different modeling methods, the existing modeling techniques can be mainly divided into geometric modeling, scanning, image based methods. The modeling technology based on geometric modeling requires professional designers to master relevant 3D software to create 3d models of objects, which has high requirements for designers and low efficiency. Scanner with its advantages of high precision and application, but because the measurement equipment itself occupies a relatively large space, easy to be limited by space, location and other factors, so as to limit the scope of use in some specific cases, and also need to carry out some later professional processing. The 3d modeling technology based on digital photos can take digital photos from different angles according to the different positions of the object. As long as the internal and external parameters of the digital camera are determined, the spatial position of the feature points of the object can be determined.
Modeling techniques in 3DSMAX
The full name of 3DSMAX is 3D Studio Max, which is an image rendering and production software based on 3D animation technology. Before the emergence of this technology, people mainly used graphics workstations for computer animation (CG) design. As this technology is based on DOS operating system, it has very high requirements for technical personnel. So it was a highly skilled job at the time. However, with the advent of 3DSMAX and Windows, the difficulty of CG design has been greatly reduced. Today's 3 dsmax has become the most widely used virtual scene production software, and is widely used in animation, film production, architectural design, multimedia production, from multiple aspects, such as games and advertising design its effect is more obvious in the film and television works, makes the modern film and television works more infectious and telepresence special effects shots. Has become the main 3d modeling software in the computer at present.
3.1 3DSMAX modeling method
In the real world, objects have different shapes, as well as various kinds of trees, flowers, characters, vehicles and other terrain objects. In order to meet the requirements of virtual reality technology for the sense of reality, modeling methods under 3DSMAX technology are also diverse, and different methods and effects are presented according to different things. 3DSMAX object modeling mainly includes polygon modeling, non-uniform rational B-spline curve (NURBS) modeling and subdivision curve modeling.  These modeling methods can select appropriate modeling methods according to the requirements of the virtual reality system to quickly complete the object modeling in the virtual reality scene.
3.2 Polygon Modeling
Polygon modeling applies to objects with regular shapes and no surfaces. The idea is to use small planes to simulate surfaces to make three-dimensional objects of various shapes. A facet can be a triangle or a rectangle or some other polygon but in practice it's a triangle or a rectangle. Using polygon modeling allows you to create basic geometry, then use the editor modifier to adjust the shape of the object as required, or combine objects through Boolean operations, lofting, and surface slice modeling to create virtual reality scenes and objects. The main advantages of polygon modeling are simplicity, convenience and speed, but it is difficult to generate smooth surfaces. Therefore, polygon modeling technology is suitable for building objects with regular shapes, so most man-made objects, currently in architectural renderings, game role modeling mostly use polygon modeling.
3.3 NURBS modeling
NURBS is a mathematical concept in computer graphics. NURBS modeling technology is one of the most important 3d modeling methods in recent years. NURBS is ideal for creating smooth, complex models with realistic details. But since NURBS modeling must use surface slice as the basic modeling unit, all have certain limitations. For example, NURBS surface has only a limited number of topologies, which makes it difficult to make objects with complex topologies. The basic structure of NURBS surface slice is meshlike. If the model is more complex, it will lead to the rapid increase of control points and the surface is difficult to control. When constructing complex models, a large number of trimmed surfaces are often required, leading to calculation errors. 
3.4 Subdivision surface technology
Subdivision surface technology is introduced to solve the difficulty of surface building in NUBRS technology. It uses any polyhedron as a control network and then automatically generates smooth surfaces based on the control network. The mesh of subdivision surface technique can be arbitrary shape, so it is easy to construct various topological structures and keep the whole surface smooth. Another important feature of subdivision surface technology is subdivision, which adds detail to the local part of the object without increasing the complexity of the whole object, while maintaining the smoothness of the object.
3.5 Data optimization
Unlike the real scene, the model created by the computer is ultimately a virtual model, so its ability to optimize the processing of various data in the real world is very important. By optimizing the data, the real ideal model can be further obtained. For example, the object with a length of 1m in the actual data is compressed and optimized to 0.1m, and the 3DSMAX rendering operation is also used in the process of compression to optimize its output effect. Generally, the operation of reduction and optimization for large volume objects is relatively simple, and the model effect after output is better, but the data amount contained in them is also higher than that of small volume objects. At the same time, the data optimization technology also includes the optimization of redundant data of real objects, the optimization of data on the non-visual interface, the deletion or optimization of invalid data, etc.  in a word, no matter the optimized data belong to which type, the operator need to be both comprehensive and classified, to ensure the authenticity and rationality of the data, to avoid data loss situation, in order to avoid increased workload, can apply appropriately photos data will record the real scene, so that you can avoid data error, ensure that the overall quality of the model.
4 virtual reality technology model creation
4.1 Local model creation
After the optimization of the data, the modeling method of 3DMAX software can be used to create the local model. First, geometric modeling should be used to adjust the overall data, and then polygon modeling method should be used to adjust the points, lines and planes in the geometric figure. Finally, NURBS modeling method is used to make the object feel real and make the structure of the graph become regular. Among them, the polygon modeling operation is relatively basic, and it is difficult to create the model with complex structure. Therefore, it can use NURBS to modify the polygon graph, but it is difficult to modify the model with edges and corners. The modeling of the object should be combined with various modeling methods, but also can use the multifaceted control technology, fully cope with the more complex and detailed model.
4.2 Addition of local materials
After the initial completion of the model, the material addition function in 3DSMAX can be used to fill the local material. The material can be divided into software material and software adjusted material after two categories. The application range of external materials is relatively wide, easy to operate.  Software must be used to adjust the addition of materials that require special materials, such as shadow casting and metallic gloss.
5 Application of 3DSMAX model in virtual reality technology
5.1 Virtual Reality Technology modeling language VRML
VRML is a kind of simulation programming language which can play an influence and function on the network and can build a three-dimensional unreal space. Users using the network can browse to the 3D unreal reality created by VRML, which changes the current limitations of the interaction between the network and user applications, and makes the interaction between users and computers more convenient, thus fully demonstrating the immersion, interaction and autonomy of the virtual scene. VRML language has descriptive properties, can construct three-dimensional environment or objects. In the constructed virtual environment, each scenario is designed, deployed, and composed of many nodes, so the nodes are outlined and WRL files are generated.
5.2 Application of 3DSMAX model
VRML uses nodes to build the environment, but using nodes to describe the model is difficult to achieve a specific realistic design effect, and it is not easy to simulate the shape containing complex surface. 3DSMAX makes up for this. Create VEML file with 3DSMAX model. Import the 3DMAX model into the VRML scene. Simply put, the 3DSMAX model is exported, saved in 3DSMAX format, and then merged with VRML. For those developing and designing in VRML, most of the entities can be modeled in 3DSMAX, and the final file is in VRML form. For example, a virtual elevator in a building roaming environment. The elevator model can be built and generated using the aforementioned polygon modeling and saved as a VRML file. Then we can combine TouchSensor, TImeSensor and PosiTIonInterpolator nodes to achieve the visual effect of elevator door opening and closing. 
Virtual reality modeling technology has solved the problem of building 3d object model in virtual environment. As one of the core technologies of virtual reality technology, it fits the sense of reality required by virtual reality technology. It can also be applied to many other fields. Just like other emerging science and technology, virtual reality technology is also the product of the intersection and integration of many related disciplines. We must clearly realize that although the technical potential in this field is huge and the application prospect is also very broad, there are still many unsolved theoretical problems and unovercome technical support. However, its unique advantages and specialties provide a new breakthrough for the development of various fields. At the same time, I believe that with the rapid development of network technology, virtual reality technology will get more rapid development, will be widely used in human daily life, bringing a new look to people's life.
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