摘要
随着计算机技术和网络技术的迅速发展，利用网络进行知识传播已经成了打破时间和地域限制的一种有效的教学方式。在WEB上进行交互式教学，可以实现图文并茂、声音动画等综合信息的传递，提高了学生的兴趣，使得课堂教学生动活泼，更易接受。
然而，工程图学的远程教育与其他的课程有所不同。在其教学过程中，经常需要进行由3D零件到2D图形、又从2D图形回到3D零件的空间思维活动。怎样通过网页上的文字和图形表达这些概念并且实现对学生的空间想象能力和用二维图形表达三维形体能力的培养，这是工程制图远程教学的难点及重点。因此，必须提出一种全新的构筑网络课件的方法来代替传统方法。为了解决这一问题，我们采用了网上的三维建模语言VRML和JAVA实现三维模型的交互控制，采用了网络3D建模工具，如Viewpoint、Cult3D等进行网上三维形体展示。
本文利用VRML、Java3D、HTML编程语言，结合AutoCAD、3DSMAX、Photoshop等图形软件，Cult3D、Viewpoint、Flash等网络动画制作工具，探讨了将Web3D融于工程制图远程教学系统中的方法。在系统中，对平面零件图纸的展示，使用了AutoCAD2002中附带的Volo View插件；对于三维模型的演示，使用了VRML建模语言；对于装配图的阅读配置了动画演示，使用了Web3D制作工具。为了减少三维动画文件大小，使之利于网络传输，我们采用了流媒体格式。将三维动画视频文件转换为流媒体传输，大大地增加了传输速度，而图像质量不受影响。本文主要使用了两种网络流媒体格式——swf和rm。使用Macromedia Flash
Player插件以及swift3D，将3DSMAX中制作的三维动画转换成易于网上传输的swf矢量形式；对原始三维视频avi文件进行压缩，成为rm流式格式；本文灵活运用这些方法，有效地解决了网上三维数据传输带宽限制的问题。
此外，为了克服图片对网络传输速度的影响，本文还对图像压缩技术作了一定的探讨，介绍了JPEG方法、小波变换方法和分形方法在图像编码中的应用，并用软件实现了这三种压缩，对它们的压缩效果进行了比较分析。在此基础上，本文提出了一种新的图像压缩方法—“小波变换与分形预测结合的图像压缩”方法。这种压缩编码方法结合了小波变换与分形理论的特点，理论上能够有效的改善压缩比率和压缩品质。本文对这个方法的可行性和实现方法作了一定的研究与探索，对其压缩效果进行了预测分析。
With the rapid development of Computer Technology and network, spreading knowledge through network has been an efficient teaching method, which breaks through the shackle of time and area. Interactively teaching on web makes it certain to provide compound information of pictures, words, sound and animations. So, students' interests are excitated and the teaching becomes lively and ready to be absorbed.
However, long-distance teaching on Engineering Drawing is different to other courses, because during the teaching, we'll often transform the 3D parts into 2D graphics and imagine the 3D archetypes in our mind. How to express these concepts and realize to train students' abilities of space imagining and expressing 3D models by 2D lines is the difficulty and emphases for Engineering Drawing. So a new method for constructing an internet courseware must be put forward to replace the traditional method. In order to solve this problem, we use JAVA and a Web3D language named Virtual Reality Modeling Language(VRML) to implement interactive control on 3D models. Other Web3D modeling methods are used to show 3D models on web.
In this paper, a VR Engineering Drawing long-distance education system is developed based on web, by using some graphics softwares, such as VRML, AutoCAD, 3DSMAX, Photoshop etc., and some Web3D animation tools, such as Cult3D, Viewpoint, Flash and so on. In this system, we use a plug-in called Volo View to realize showing detail drawing interactively; use VRML to construct 3D models; use Web3D tools to show assembly animations. In order to reduce the size of 3D file and make it easy to be transmitted, stream media fonnat is adopted here. The transmission speed is greatly heightened and the video quality remains impervious by converting 3D animation video to stream media. In this paper, we
mainly use two types of stream media format-swf and rm. A plug-in named
Macromedia Flash Player and a tool named swift3D are used to realize showing 3D animation which is made in 3DSMAX and then is converted to swf format, a vector format that is easy to be transmitted by internet; Compress original 3D animation
video (avi format) to rm stream media format. All these methods are used skillfully in this paper, thus the limit of transmission bandwidth of 3D data on web is get over. Besides, in order to overcome the obstacle that more pictures in webpage result in slower network transmission speed, we have a discussion on image compression technology in this paper. JPEG method, wavelet transform method and fractal method are introduced here. We program software to realize these two methods and to compare their capacities. In addition, we present a new image compression
algorithm based on both wavelet transform and fractal theory-"Wavelet
Transform and Fractal Predict for Image Compression", which theoretically enable to improve the compression rate and quality efficiently. We have done some research and exploration on the feasibility and implementation of the compression method and prognosticated its capacity as well.
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