A Java3D application for visualization and deformation of CAD models in Virtual Reality.

Cioi, Daniel

Abstract: This paper presents a developing application, part of the author's PhD work title: Virtual Reality for Computer Aided Design". The application combines two systems: Virtual Reality system with its special equipments for visualization and manipulation and CAD system recognized as basic systems in the design process. Based on the slogan: "Write once, run anywhere", the author chose Java language and Java3D API to develop this application.

Key words: Java3D, CAD, Virtual Reality, Visualization.

1. INTRODUCTION

Virtual Reality is a computer artificial environment that allows a user to view, explore, and manipulate the environment. Virtual Reality is commonly manipulated and explored using various input devices such as goggles, headphones, gloves, and/or a computer. Using these devices a user can browse throughout a virtual world or pickup and manipulate virtual objects (Computer Hope 2007).

CAD is abbreviated from Computer-Aided Design. It's a special software package which allows engineers and architects to design products with precise shape of parts. The design is made with part representation and modular parts in 2D or 3D.

With traditional two-dimensional (2D) based interfaces, such as a mouse or a keyboard, many CAD models, like automobile bodies, industrial products, and ship hulls, are difficult to design and edit due to their three-dimensional (3D) nature. For example, to create and modify a loft surface or model, designers have to deal with the surface construction curves. Surface shape is difficult to control, as it depends on the number, shape, and position of the section curves. Interactively designing surface is often a tedious, inefficient and iterative process (Liu et al., 2004).

According to (Bell) there are two main hypotheses that can be made regarding the advantages which virtual reality could bring to computer aided design based on the facilities an immersive virtual environment can provide. These are as follows:

* Improved visualization of product by allowing the user to co-exist in the same space as the product model therefore gaining a better appreciation of product geometry and aesthetics.

* Improved interaction with design in terms of more intuitive model manipulation and functional experimentation, the designer could effectively interact with the product model directly rather than using the conventional 2-D mouse and cursor.

The application presented in this paper, named VRforCAD, is a solution for this problem. The CAD models in DXF and STL formats are imported and visualized in a Canvas3D in active stereoscopic mode. The 3D models can be manipulate (rotate, zoom, translate) and modify its surfaces by pushing, pulling and dragging. At the end, the models can be exported in DXF or STL format to be compatible with CAD system. The stereoscopic principle is described below.

Stereoscopic display technology family of products enables high-definition stereoscopic viewing in an electronic environment. This concept is known as Stereo3D. Stereo3D delivers the most realistic visual representation possible of complex digital solid models. This provides engineers and scientists with a significantly better understanding of three-dimensional information and yields levels of technical proficiency not available using a typical 2D view (StereoGraphics Corporation).

The key principle of active stereoscopic visualization is fast switching between two different images. Monitor, special TV or special DVD projectors very fast switches during the visualization between left and right eye images. Special glasses (soled usually shutter-glasses) a connected through IR or by a cable with the projection device. Odd images are visible only in one eye; the even images are visible in the second eye. The glasses use fast switching LCD panel for hiding the image from opposite eye. For enough high frequencies (100 Hz and higher) the switching is hard to notice. For lower frequencies, the quality of stereoscopic perception is affected by flickering problems. This system could be used in combination with PC monitor efficiently (GALI-3D Company).

One of the great advantages of active stereoscopic projection is standard projection screen usage.

2. APPLICATION DESCRIPTION

Java technology is an object-oriented, platform-independent, multithreaded programming environment.

Platform independence means that programs written in the Java language must run similarly on any supported hardware/operating-system platform. One should be able to write a program once, compile it once, and run it anywhere.

Multithreaded means that a single Java program can have many different threads executing independently and continuously.

[FIGURE 1 OMITTED]

The Java 3D API is a hierarchy of Java classes which serve as the interface to a sophisticated three-dimensional graphics rendering and sound rendering system. The programmer works with high-level constructs for creating and manipulating 3D geometric objects. These geometric objects reside in a virtual universe, which is then rendered. The API is designed with the flexibility to create precise virtual universes of a wide variety of sizes, from astronomical to subatomic (Java3d, 2007).

The cross-platform capability was the first reason to choose this language for developing the VRforCAD application. The application contains a Canvas3D, a SWING panel with buttons and check boxes on the right, menus on the top and dialogs. Fig.1. shows a screenshot of application running on WinXp.

When a CAD file is loaded, the application scan the CAD file, convert it in .vfc file which then is loaded in arrays used to create the geometry by GeometryArray object with By References method for rendering it on the Canvas3D.

The CAD applications use parametric surface for describe the 3D models and the result object still appears smooth when the deformation is conducted on the control points, while the VRforCAD application use triangles to draw the geometry where too few point are sampled and results a non-smooth deformation.

Thus for deformation of 3D models surfaces, the author made a method which based on the index position of vertex in arrays received from the picking operation perform a recursive search for the nearest vertices and move it along the deformation direction. The deep of recursive search and deformation is controlled by a factor of dissipation. Fig.2a. and Fig.2b. present the difference between using and not using this method on a 3D model of a car component: mudguard. For a better understand on this example is used the wireframe mode for visualization.

At this moment, for manipulate de 3D models is used a mouse device and the deformation operation is performed in combination with the "z" key. At the initial was chose the Meta key for its presence on any personal computer's keyboard, but on Linux this key has another function (in combination with mouse perform resize of desktop windows).

[FIGURE 2 OMITTED]

The current features of VRforCAD application are:

* Rotate, zoom and translate operations for the 3D models;

* Import/Export DXF and STL CAD formats, also the models can be kept on its own format *.vfc;

* Options for modify material appearance;

* Options for modify the properties of the scene lights. There are two directional lights, two points light and an ambient light;

* Option for Wireframe visualization;

* Option for Stereoscopic view (on this moment just active stereoscopic);

* Option for dynamic section;

The application is tested on WinXp, Linux Suse and FreeBSD. The follow table presents the configuration used for testing and development.

3. FURTHER WORK

The next step is to add the facility to deform the 3D model surfaces by a primitive like a ball and a tool like a brush to paint the surfaces.

The mouse will be replaced by a SpaceBall 5000 (a 6 degrees of freedom input device developed by 3Dconnexion, the device is designed to ease navigation in 3D computer models) and a haptic device "Phantom Desktop".

Also the results of this work will be presented on a web page (www.vrforcad.org).

4. CONCLUSION

The VRforCAD application makes some steps toward the use Java and Java3D API to develop more complex Virtual Reality applications.

5. REFERENCES

Bell, M. Available from: http://www.cs.ucl.ac.uk/staff/M.Bell/prjdef.html Accessed: 2007-05-30

Computer Hope, Available from: www.computerhope.com/jargon/v/vr.htm Accessed: 2007-05-30

GALI-3D company, Principles of active stereoscopic visualization, Available from: http://www.gali-3d.com/en/techno-active-stereo/techno-active-stereo.php Accesssed:2007-05-30

Java3D Tutorials, Available from: http://wiki.java.net/bin/view/Javadesktop/ Java3DBooks Accesssed:2007-05-30

Liu, X.; Dodds, G.; McCartney, J. & Hinds, B.K. (2004). Virtual DesignWorks--designing 3D CAD models via haptic interaction, Computer-Aided Design, Vol. 36, No. 12, (October 2004) 1129-1140.

StereoGraphics Corporation. Stereo3D Hardware Developer's Handbook, Available from: www.stereographics.com/x_downloads/guides/hdk.pdf Accessed:2007-05-30

Table 1. The configuration used for testing the VRforCAD application.

OS WinXP Suse SLES 9.3 OpenSuse 10.2

JDK version 1.6 1.4.2 1.5
Java3D version 1.5.1 1.4.1 1.5.0
Video Card ATI ATI FireGL Nvidia
 FireGL X3-256 Quadro
 2 FX 1400
Procesor 3500 1.6 2.4 P4
 AMD IA64 Intel