Abstract: - Adria-Mobil Ltd. is a well-known Slovenian caravan and motorhomes producer, which implemented CAD system years ago. Development and use of ...
Visualisation and Optimisation of Motorhome Prototypes Using Virtual Environment Techniques GORAZD HREN, BORUT GOLOB, ANTON JEZERNIK Faculty of Mechanical Engineering Maribor University of Maribor Smetanova 17, 2000 Maribor SLOVENIA
Abstract: - Adria-Mobil Ltd. is a well-known Slovenian caravan and motorhomes producer, which implemented CAD system years ago. Development and use of CAD system resulted in ideas to extend CAD system with VR techniques for visualisation and optimisation of physical prototype, not only the shape geometrical data but also to combine different materials and textures of interior and interior functionality. A new low-cost system has been developed that enable the change of CAD model in VR environment. VRML as ISO standard that allows the distribution of computer models over the Web is applied. The underlying principles of Web-based VR with VRML and data base connection are described. Key-Words: - CAD, virtual reality, virtual environments, VRML, data base, visualisation
1 Introduction ADRIA Mobil Ltd. is a well-known as one of the leading European producers of motorhomes and caravans, and company intention is to preserve that status. Since the beginning of the caravan production in 1965, Adria belongs among asserted, traditional producers of caravans. A high market share on the richest and most demanding European markets is a result of high quality products and European-wide sales network. The company is mainly oriented to export in west European countries and is present on the market of middle Europe and Japan. Every market has its own technical regulations, different customer fancies and needs that significantly increase the number of variations of produced models. Considering the amount of production and number of employees the company could be recognised as middle size enterprise in the branch.
production cycle is quite characteristic, the prototypes are presented at the specialised fairs and the response is used for improvement off the final documentation preparation. Equally important are after sales activities with a great impact on quality improvement and further development guidelines. To produce a prototype of motorhome demands a lot of negotiations throughout design process. The optimal arrangement of interior should be achieved due to very limited space and comfort requirements. Multifunctional elements have been used to perform effective use. A lot of analyses should be done of narrowness of the interior spaces, accessibility and operability of inbuilt components. Major analyses are performed on physical prototype what is very time consuming and expensive task.
Fig. 1: Adria motorhome outlook. The competition on the market is very sharp and consequently the companies are forced to improve the quality of the products very often by adding new features or refresh the outlook and the interior design. The
Fig. 2: Two different layouts (day & night).
2 CAD and Virtual World The current demand to reduce the time and cost involved in product development is forcing companies to use the new technologies to accomplish goals at the market. Computer-Aided Design (CAD) systems with solid modelling and parametric design are powerful tools for creating and modifying the objects but are still not able to provide all the support that designers need to effectively perform the design task. There are many CAD visualisation applications available, directly from particular CAD system or neutral viewers that use metafiles [1]. Virtual Reality (VR) is emerging technology that provides the user with information that cannot be obtained from CAD systems. One drawback in CAD systems is that the designer is limited to the size of the viewing area of the monitor. A large part or assembly must be viewed separately or scaled with limited view. With new 3D input and output devices a designer can be immersed in virtual environments. Input devices assure realistic interactions with virtual objects and support the control of virtual worlds. The virtual environments could deal with navigation in 3D space and allows capabilities as lookaround, walk-around and fly-through. Nowadays, the terms Virtual Reality (VR) and Virtual Environments (VE) are extended from initially full immersive systems to semi-immersive systems, like large screen projectors and even non-immersive systems, like monitor based viewing of 3D objects [6]. Originally, VE was referred as full immersive, where the user is fully immersed in an artificial, completely computer generated world. The unique characteristics of such system are: • Stereoscopic viewing for depth and sense of space perception. • Virtual world is proportional to human size. • Input and output devices (e.g. data glove) enable interactions for control the virtual world. • Head-referenced devices provide a natural interface for the navigation and viewing. • Shared or distributed VE via network applications allow communications and interactions of different users to participate in the same VE. • Using non-visual techniques (audio, tactile,) to amplify the user illusion of immersion and presence in virtual world. Virtual Environments are developed and used in several research groups at the universities and companies. As happened with CAD applications the leading companies in VR technology come from automotive and aircraft producers mainly to support
ergonomic analyses and assembly and maintenance inspection [2] [3] [4]. VR techniques require a significant computer power to provide a basic requirement as viewing and interactions with real-time response. Large companies lack the time and small companies lack the resources required to implement the technology and automation needed to compete in market place. Non-immersive VR systems features are far from possibilities of immersive VR systems, but a key element in non-immersive systems is in standardisation of IT techniques that could be used - Virtual Reality Modelling Language (VRML).
3 VRML and Virtual Model The VRML as standardised addition to Web browsers represent a great potential that allows the visualisation and distribution of 3D virtual models over the Internet. The Viewing of VRML models via VRML plug-in for Web browsers is enabled on monitors with mouse to control the virtual world, although not like in immersive systems, but functional and interactive. Models have all the attributes or features of virtual models. Descriptions of models are in polygonal representation for fast rendering, they include methods for animations, functionality description and user interactive control. The virtual world is defined in VRML text files with standardised syntax and can be viewed with free-ware plug-ins in common Web browsers. The plug-ins enables standard navigation tools and interactions with mouse as input device. As the system required for VRML is very low-cost (PC, network, free-ware plug-in) and is standardised it represents promising and strong research base for various applications. The network speed and computer power are the limitations for broad use that is under development and acceleration throughout. VRML procure a powerful tool for visualisation of information and representation of 3D virtual objects. For viewing the geometry, the model needs to be enriched with additional information like appearance (colour, textures), lightening, animations, sounds and environmental aspects to give the more realistic view of objects. Navigation Info Geometry Appearance
Light Sound Animation Interaction Scripting
VRML 2.0
Web Browser
Fig. 3: VRML file definition.
The VRML model in file consists of standardised descriptions of nodes as building blocks that are organised in hierarchical scene graph. Geometry and appearance of objects is defined in shape nodes, the functionality and behaviour is defined through sensor nodes and routing mechanism. The main tool for interactions are sensor nodes that track the user position defined via navigation tools from plug-ins or the position of the input device (mouse). The predefined events are triggered with routing mechanism when the position of the input device is determined with clicking on shape. The routing mechanism is used for predefined events; more flexibility is added with Script nodes. In Script nodes the behaviour can be programmed with program languages as Java, JavaScript or VRMLScript. The models generated with CAD system using 3D modelling techniques. For fast real-time rendering only polygonal representation of the geometry is useful. Objects or parts created with hybrid CSG and B-rep representation in CAD system must be converted into polygonal mesh of triangles with approximation algorithm, the number of polygons determines the accuracy of appearance and it is inversely proportional to the rendering speed. For complex geometry a substantial computer power is required. We have to keep in mind that VRML was not designed specifically for engineers, although we use it for engineering tasks as design, operational simulations, etc.
4 Application Underlying Principles Our goal is to develop a system that enables: • Visualisation of prototype design for all possible participants in design process with various design and computer knowledge. • Merging objects into VE from additional systems (as electric installation). • Walk-through viewing and evaluation of geometry data adjustment. • To check the interior material reconciliation. • Changes of object’s attributes and parameters, as colour, texture and possibly even geometrical parameters. • Inspection of interior operational tasks (switching lights, changes seats into bed, etc.). • Analyses of narrowness of the interior spaces, accessibility of inbuilt components (toilet or kitchen block).
• •
To propagate changes into CAD system, so no wellknown iteration loops are needed for refreshing the CAD model. Using the VRML standard file system with no additional input and output devices needed.
A VRML representation of a part is a polygonal approximation of the original CAD model and as long it is approximation it cannot replace the CAD model. During converting CAD model into VRML the crucial step is performed. The VRML model could not be converted back to CAD system with all features available in CAD system. This conversion is irreversible. Changes and additional information in virtual model cannot be reproduced in the CAD system. CAD system model
VRML model
Additional Info
Fig. 4: VRML file generation from CAD model. As we need a possibility to propagate changes from VRML model to CAD system and meanwhile the features of VR techniques for visualisation and functionality control a newel approach is proposed. The new application is under development that opens two windows, one with geometry parameters organised as hierarchical tree and another for VRML model visualisation. In the first window the geometrical data with all parameters are presented and could be changed. Those parameters include geometry definition, colours and textures. In the second window the VRML model is generated with changed parameters allowing navigation through the model and explore predefined animations and objects functionality. For every parameter change the new VRML model is rebuilt. In the CAD database it is not all information needed for VR system so a new database is generated where CAD model is expanded with additional data dealing with VR functionality, as sensors, routing, textures, lightening, different view definitions, and avatar definition for collision detection. The user could progress through VE and inspect the interior. If the user wants to change any parameter it could be accessed in the first window, changed and afterwards refreshed in VE. As CAD model features are not directly accessible, the conversion from CAD system into database is performed via standard interfaces (STEP, VDA) [7]. With conversion some features available in particular CAD system are definitely lost, but on the other hand, it is easier to merge data from different CAD systems or additional applications, like VRML editors, 3D
Additional applications CAD SYSTEM
U S E R
MODELING ENVIRONMENT
DATA CONVERTER DATA MANAGER
DATA INTEGRATOR
DATA ENVIRONMENT
DATA BASE
Application
Web Browser
VIRTUAL MODEL
VRML Model
VIRTUAL ENVIRONMENT
Fig. 5: Application model schema. StudioMAX, etc. That description allows converting geometry data back to CAD system.
routing mechanism provide inspection and evaluation of functionality and behaviour.
As VRML files are organised in parent-child hierarchical structure where models represent subparts of the virtual world, it is a quite straightforward task to create large worlds, specially reusing subparts and inherit attributes. To avoid huge files, that increase the downloading time, the inline node is used to merge objects. Designer from CAD system provides the motorhome model. All parts are modelled and organised as assembly tree. Every part is represented as object or model file from CAD system. The advantage of that mechanism is enormous, because it allows preparation and testing of individual parts and incorporating afterwards into complete virtual world. Models generated from VRML editors and CAD systems are composed from many complex, nested and repeated structures, far from optimal code and must be optimised. As models are complex we proceed with optimisation attempts to keep file size as small as possible. Two methods are used for optimisation: LOD (level of detail) and reducing the texture map size. The level of optimisation depends on the level or stage of virtual world development. A significant manual work is needed for optimisation and reduction of polygonal approximation for the virtual model. An application generates the VRML model that is viewed via Web browser that allows low-cost nonimmersive VE. The application illustrates the motorhome interior of an ongoing design by Web. The layout and interior arrangement can be inspected and evaluated simply by walk-through navigation, the
Virtual model is more intuitive and easier to negotiate about than blueprints. The results of negotiations are much easier to accomplish and a physical prototype that are build for fairs need less changes if at all.
5 Conclusion An application is under development and testing stage working only in the company, but we have to consider broad use in the future. VRML has made VR accessible through Web to all sorts of users, additionally this low-cost technology enables designers to exchange and develop virtual models worldwide. Since VRML worlds are delivered across the Web, we must consider the network bandwidth and navigation speed. The overload of polygon rendering may result in reducing the sense of presence and the capability of interaction. The copy of CAD model must be protected as company property so the password protected Web site or encrypting could be a tool for protection. The virtual model contains not only geometry but functionality as well. Once the model is defined it could be used with any VR system, from full immersive like HMD to non-immersive like a monitor-mouse combination. To use the virtual model in immersive VR the functional description must be replaced or removed for viewing the model. Using the model in HMD system could be very impressive and allows analyses of
attainability, accessibility, visibility and performing operational tasks in more realistic way. Virtual engineering is a tremendously useful tool for engineers because it provides the capability to watch how a part or product reacts under real-world conditions during different phases of its functioning. Creating virtual model is still very time consuming task, although objects are created in CAD system. The usage of CAD system in Adria company is well adapted and in extensive use [8]. It is very easy to create simple virtual models with VRML editors with no knowledge of VRML syntax, but real industrial models are rarely simple and for real problems VRML editors, like Spazz3d, are seldom useful and profound knowledge about syntax and data formats is needed. The routing mechanism is not trivial if you need to add interactively triggered processes during navigation. The functionality and capabilities of the next generation of CAD systems have to stand extensive changes due to technological advances in: • High performance computing and communication. • More focus on the conceptual design phase. • The use of advanced technologies such as VR. We focus on last one and optimisation and visualisation possibilities with low-cost VR application of the interior design of motorhomes represent significant change in prototype building process. One picture is still worth a thousand words, but one animation is worth a thousand pictures.
References: [1] Mahoney D.P., All eyes on CAD. (3D visualization tools), Computer Graphics World, May, 1999. [2] Matthias B., Immersive User Interaction Within Industrial Virtual Environments, Virtual Reality for Industrial Applications (ed. Fan Dai), SpringerVerlag, 1997. [3] Gomes de Sa A., Zachmann G., Virtual reality as a tool for verification of assembly and maintenance processes, Computers & Graphics, Vol. 23, 1999, pp. 389-403. [4] Kasik D.J., Viewing the Future of CAD, IEEE Computer Graphics and Applications, Januar/Februar 2000, pp. 34-35 [5] Regli W.C., Cicirello V.A., Managing digital libraries for compuetr-aided design, Computer-Aided Design, Vol.32, 2000, pp. 119-132. [6] Gao S., Wan H., Peng Q., An approach to solid modelling in a semi-immersive virtual environment, Computer & Graphics, Vol. 24, 2000, pp. 191-201. [7] Pratt M.J., Anderson B.D., A shape modelling applications programming interface for the STEP standard, Computer-Aided Design, Vol. 33, 2001, pp. 531-543. [8] Hren G., Jezernik A., Lukšiè S., Experience s of CAD Implementation and Trends in Development at ADRIA Mobil Ltd., Journal of Mechanical Engineering, Vol. 46, 2000, pp. 770-779.
