方法和系统虚拟漫游在水利工程

Method and System for Virtual Roaming in Water Conservancy Works

Seng Dewen Song Zhechen

Department of Computer and Information Engineering

Zhejiang Water Conservancy and Hydropower College

Hangzhou, China

sengdw@https://www.360docs.net/doc/a09420975.html,

Abstract—The advances in the research of virtual roaming techniques in water conservancy works are reviewed. Main process to construct a 3D virtual environment for water conservancy works is introduced. Key techniques and the difficulties with their solutions in the application of virtual roaming techniques to water conservancy activities are analyzed and summarized. A development framework for building 3D virtual roaming system is presented to illustrate the application potentiality of virtual roaming techniques in computer aided system for water conservancy works. The methods for the visualization of complex water conservancy works environment is described in detail. Aspects like presentations of data with spatial dependence, virtual roaming in the terrain and geographical frame of reference and in time, interaction techniques are presented. An interactive virtual roaming system for the water conservancy work from China is used as an example to demonstrate the effectiveness and efficiency of the techniques discussed.

Keywords-virtual roaming; water conservancy works; system simulation; 3D visualization; interaction

I.I NTRODUCTION

The real world is an extension of the three-dimensional (3D) space. In the past, because of the limitations of cognitive ability and technology levels, the simulation of the real world is mainly in two-dimensional (2D) forms. However, 2D simulation is a kind of abstract. It is only a simplified aspect of the objective world. It can not effectively express the real world objects and phenomena. To some extent, it brings a certain amount of limitations to our understanding of the real world and our capacity to change the world. In recent years, as the increasing development of realistic image rendering technique and hardware capabilities, it has become possible to better describe and simulate the real world; hence, 3D visualization in medicine, meteorology, geology, marine, mechanical design , finite element analysis, and many other fields has been widely used [1-6].

In our study, we construct a true 3D virtual scene of the water conservancy works by computer graphics and visualization technology, and provide a good human-computer interaction, including real-time translation, rotation, scaling, arbitrary cutting display and virtual roaming so that observers can observe the whole water conservancy works from different angles and different level of details, which will undoubtedly be more intuitive and effective in the decision-making process of the water conservancy workers and researchers.

II.C ONSTRUCTION OF 3D VIRTUAL SCENE The 3D scene is a collection of all visual objects of the simulation system. In general, the shapes of these objects can be constructed with points, lines, and surfaces. Cutting, anti-aliasing, shading, lightening, texture and material properties are used to make the objects become more realistic [7-10]. The construction of a real 3D virtual scene generally goes through the following steps:

1)Geometric modeling. It is to construct all the objects in the 3D virtual scene with geometric elements. It mainly uses mathematical methods to establish the required geometry to describe the scene, and then put them into the computer. This part can be made by the 3D modeling system. Geometric descriptions of the scene directly affect the accuracy of graphics and the cost of rendering, therefore, to choose a reasonable and efficient means for the data representation is extremely important.

2)Physical modeling. Physical modeling is the processing of color, light, material and texture of the visual objects. It will finally convert the geometric elements and their visual characteristics into graphics or images.

3)Setting the scene. Before rendering the scene, we need to set the relevant parameter values of the scene. These parameters generally include the properties of light source (mirror light, diffuse light and ambient light), the position (distance and direction) of light source, shading mode (smooth or flat), texture mapping mode and so on. In addition, we need to set the viewpoint location and direction.

4)Rendering model. It is to transform the 3D scene into the 2D images on a computer screen by projection transformation which can be divided into two cases: orthographic projection and perspective projection. The major characteristic of orthographic projection is that no matter how far from the projection screen, the size of the object remains unchanged after projection. This projection is usually used in drawing an architecture blueprint and computer-aided design. In these industries, the size and the angle between object need to remain unchanged after projection, so that the construction or processing of the objects will be in the correct size and proportion. Perspective projection is more in line with the mental habits of human-

2009 International Conference on Intelligent Human-Machine Systems and Cybernetics

beings, that is, the objects after projection will look larger when they are closer to the viewpoint and smaller when they are further away from the viewpoint. In virtual scene, perspective projection is generally used to better simulate the real world.

The final results of this process are to show the entire 2D images of the 3D scenes on the computer screen.

III.V IRTUAL ROAMING S YSTEM F RAMEWORK When the 3D virtual scene has been constructed by visualization technology, the system must provide a certain degree of human-computer interaction functions that enable users to better understanding and awareness of the objects in the scene, as well as the relationships between the objects. In all means of human-computer interaction, interactive roaming is the most important virtual observatory means. To this end, we design the system framework of a virtual roaming system as shown in Fig. 1.

Interaction of the rendering and displaying of the scene is all controlled by the user. The inputs of the user mainly refer to the keyboard and mouse input devices. They will be interpreted into a series of control commands for the management of scene’s data, the load of the geometric models, the settings of the objects’ illumination, material properties, transparency, as well as the viewpoint direction and location. The rendering module can render and display the scene dynamically and real-time based on the user’s input. In this process, the objects’ collision detection can be conducted according to the distance between the viewpoint and the objects [11-13].

IV.T HE IMPLEMENTATION OF VIRTUAL ROAMING

In the virtual roaming of water conservancy scene, the observer can use mouse or keyboard to control the location and direction of the viewpoint. When the location and direction of the viewpoint changed, the position and direction of the objects in the scene relative to the observer is also changed. In the virtual roaming system, the viewpoint is the "incarnation" of the human eyes. Its functions are similar to those of a camera in the real world. The essence of roaming process is to change the direction and location of the viewpoint; then a 3D animation in the virtual scene comes into being. Our study provides a simple controlling method to roam in the 3D scene using the keyboard. A.Process of keyboard command for virtual roaming

Keyboard roaming means the users navigate in the 3D scene through the manipulation of the keyboard. The users can roam and observe the scene flexibly and accurately. The course of roaming is to change location or direction of viewpoint in accordance with the keyboard commands and then render the scene. In general, keyboard roaming commands includes turning left and right, going forward and backward, going up and down, looking up and down, translating to left and right and so on. In our approach, we can calculate the new coordinates of the viewpoint and the reference point by decomposition computing of the space vector. For example, when in response to forward (backward) order, the viewpoint and reference point coordinates can be calculate using the following formula:

1)Viewpoint coordinates (speed stands for the moving speed, angz stands for the rotation angle of the sight line around the Z-axis)

vEyePt.x = vEyePt.x + (-) speed * sin (angz);

vEyePt.y = vEyePt.y + (-) speed * cos (angz);

vEyePt.z = vEyePt.z;

2)Reference point coordinates (updown_ang stands for the sight line with the XY plane or elevation angle) vLookAtPt.x = vEyePt.x +150 * sin (angz);

vLookAtPt.y = vEyePt.y +150 * cos (angz);

vLookAtPt.z = vEyePt.z +150 * sin (updown_ang);

The constant 150 is used to maintain a certain distance between the viewpoint and the reference point.

B.Record the roaming path

Roaming operation through the keyboard to achieve real-time 3D scene is flexible and convenient, but users continue to press the keyboard seemed to be somewhat cumbersome, especially when users need to repeat the previous process. To this end, the system designs a process to record the keyboard roaming functions (record the roaming path). The recorded keyboard roaming process is known as history record. The history roaming records can be re-broadcast to achieve the process of roaming [3].

The process to record keyboard roaming is as follows: First record the initial viewpoint, observation point, the rotation angle around Z-axis of the sight line, and the elevation, etc.; then for each kind of continuous keyboard command record them according to their "action type and operation number". The purpose is to explain the entire keyboard roaming process as roaming command sequences. Finally, execute the historical record commands contrary to the record process, i.e., read the initialization parameters from the document and set the system in accordance with these parameters, and then read the sequences of the keyboard commands and call the appropriate command handler for processing.

V.KEY TECHNIQUES

A.Realistic Iimage Rendering Technology

To achieve a true 3D simulation of the water conservancy environment, including the natural phenomena such as the

Figure 1. The system framework of virtual scene.

terrain, water system, plants, canals, etc. and the real man-made buildings, we need to use realistic image rendering technology including anti-aliasing, shading, illumination, shadow, material texture, blending and atomization techniques [14-16]. Photorealistic rendering directly affects the authenticity and visual effects of the scene, however, the realistic rendering and real-time rendering is two issues against each other. In many cases, we should strike a balance between them [17-18].

B.Level of Detail

It is an effective method to control the complexity of the scene by providing different levels of detail of the objects [9]. In the graphical display of complex scenes, when the objects farther and farther away from the viewpoint, the users can no longer distinguish many details of the structures of the objects; therefore, when drawing a distant object, it is totally unnecessary to describe the complex details of the object. It will waste resources and graphics processing time. Therefore, in order to improve the graphics rendering speed to meet the requirements of real-time rendering, 3D objects are generally rendered with a wide range of accuracy in accordance with the locations of observation point. When the locations of observation point changed, the system will choose different accuracy models to be drawn. This is the so-called level of detail (LOD) technology.

C.Collision Detection

Some objects in the 3D scene can be passed through, and some are not. For example, the buildings and mountains can not be passed through. When roaming, the objects that can not be passed through require collision detection. Collision detection is to detect the distance between the viewpoint and the object, and then restrict the location relationship of the viewpoint and the object when roaming. If the distance of the viewpoint and objects is less than a certain threshold, the collision occurred. At this time, the system need to give a reasonable response to the collision, for example, make the viewpoint backward a little, change the direction of the sight line, maintain a certain distance between the viewpoint and the object or pan left or right.

VI.C ONCLUSION

Based on the methods described above, the authors developed a 3D simulation system for water conservancy works. The methods efficiently facilitate the realization of the interactive virtual roaming in a true 3D virtual scene of water conservancy works. Through effective organization and management of the objects in the virtual 3D scenes of water conservancy works, the system increasingly improves the graphics rendering speed and the interactive response time. The users can roam interactively in the 3D virtual scene real-time by the keyboard commands. The virtual roaming is fast, fluent, real, and effective. Fig. 2 to 4 are the application of the methods and the system in the real data of a water conversancy work of China. They manifest the interactive process of users roaming in the true 3D virtual scene of a water conversancy work with a different location of viewpoint and different direction of sight line. Further research is under way, with the aim of integrating all the objects in the water conversancy works into the 3D virtual scene and providing more ways of interactive roaming.

Figure 2.

An aircraft simulates the user’ viewpoint and sight line

Figure 3.

Virtual roaming (trun right) in the 3D scenes

Figure 4. Virtual roaming (trun left) in the 3D scenes

A CKNOWLEDGMENT

The authors wish to thank the research foundation for doctoral programs of education ministry of China for

contract 20060008005, the foundation of science and technology department of Zhejiang province of China for contract 2006C33057, the foundation of water conservancy department of Zhejiang province of China for contract RC0847, and the foundation of education department of Zhejiang province of China for contract Y200805387, under which the present work was possible.

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