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Picture this: visualization tools for CAD drawings.

Rendering Software is growing in popularity as mechanical engineers learn to accept the values of photo-realistic images for communicating design ideas.

Computer-rendered images have traditionally been readily distinguished from the real-life objects they portrayed. However, today, the other-worldly quality of those computerized images appears anachronistic given the photo-realism of state-of-the-art rendering packages now available.

Many rendering systems will accept CAD drawings as a sort of skeleton on which to build. Visualizations are created after CAD models have been developed and analysis results studied. The resulting images serve as virtual mockups, final electronic proofs of concept before physical tooling begins. For example, the Advanced Visualizer system from Wavefront Technologies of Santa Barbara, Calif., a package representative of the marketplace, is described by the company as being a communication tool for presenting ideas and products with maximum visual impact.


From a practical engineering standpoint, visualization can be used to identify flaws in a design. Having a common database between CAD and visualization systems is useful for facilitating changes. Many rendering programs have IGES and/or direct translator links to multiple design programs. In addition, some systems can import the results of finite element and kinematics analyses.

For example, the Wavefront visualization system accepts many types of CAD geometries, including wire-frame. A surface skin of polygons is added by the rendering software's drawing tools. Material properties can be assigned to various parts of the model as necessary. Through texture mapping, the virtual materials take on the appearance of the real-world materials they represent. Visualization systems have various types of texture-mapping projections, and the user can select the appropriate one for the shape being worked on. A library of textures, which can often be expanded by user-supplied entries, is provided with the systems. Wavefront also has the capability of importing still-video images to derive texture files. Users may also create their own texture files with paint programs.

Once the model has been formed, the photo-realism is created through the rendering process. Rendering is not a graphics operation, but rather a series of floating-point operations where the mathematics behind visual effects are computed. A process called ray tracing calculates the exact radiation, reflection, and refraction angles for light sources and surfaces in the image.

"Rendering is a process that can be divided up and processed in parallel," said Doug Schiff, segment marketing manager for the Enabling Technologies Group at Sun Microsystems Inc. in Mountain View, Calif., which researches visualization as it applies to Sparc platforms. Schiff explained that since rendering is basically mathematical, a given model can be partitioned into quarters, each of which can be farmed out to a separate processor. As long as each has access to the same database, the master image can be threaded or stitched back together. This increases the rate at which images can be rendered, permitting real-time user interaction with the model. "Massively parallel architectures would allow each processor to take a different ray," Schiff said.

Wavefront also supports dynamic visualization, enabling the creation of simple animations. The user specifies two or more key frames and creates a model in the appropriate position for each frame. Each progressive frame may only require a slightly modified copy of the previous frame. The visualization system will generate the movement between the frames. More complex motion can be depicted by specifying more than one key frame for particular points in the sequence. Control in three dimensions is provided by specifying locations according to x-, y-, and z-axes. Various video effects can be added to a dynamic presentation to make it appear more professional.


Realistic visualization has its place at both the beginning and the end of the design cycle. Before mechanical engineers go to work, they are often given physical or electronic sketches with some degree of detail on the project they are about to undertake. Photo-realistic renderings of conceptual designs are a way to ensure that the originator's intent is communicated to the mechanical designer.

Evans & Sutherland Computer Corp. in Salt Lake City develops advanced visualization and simulation programs and commercial graphics hardware and software. The company's newest business unit, the design software group, created the Conceptual Design & Rendering Software (CDRS) system for industrial designers so that they can create visualizations which can be transferred to CAD/CAM systems.

The CDRS system has three main components: the Product Designer, Product Renderer, and Product Animator modules. Product Designer is a 3-D surface-modeling package that uses both Bezier and NURBS-based curves. It includes some features found in dedicated surface-modeling systems, such as filleting, trimming, and surface-evaluation tools. Product Renderer contains tools for creating photo-realistic images. A color editor is used to determine the appearance of the surfaces of the model. Antialiasing software removes jagged edges on curves and surfaces. Images can be scanned into CDRS and texture-mapped onto model surfaces. The software also performs lighting, reflection-mapping, and ray-tracing functions. The Product Animator module enables users to create dynamic representations of rendered images.

According to Evans & Sutherland, the purpose of the CDRS system is to eliminate the need to create wood and clay models of automobile design concepts before proceeding to the engineering stage of product development. The process of physical modeling can cause design intent to be lost between the design studio and the engineering department. Photo-realistic images of concept models allow engineers to have early access to proposed designs and therefore to evaluate basic engineering concepts. A software solution provides for electronic transfer of geometries common to both visualization and CAD systems, improving the continuity of complex surfacing mathematics. Evans & Sutherland has translation modules to most CAD/CAM systems.


Other vendors of rendering systems have identified conceptual designers as a growing visualization market. Last September, Alias Research Inc. of Toronto introduced its StudioPaint conceptual design product at an automotive trade show in Munich, Germany. The design system is intended as a 2-D sketching system that works with the company's Alias Studio and AutoStudio 3-D rendering systems.

StudioPaint enables industrial designers and automotive stylists to create concept sketches on the computer that otherwise would be done on paper. The system uses a "digital vellum" approach, wherein designers develop their sketches using multiple independent layers. The designer can sketch and paint on any layer without affecting the others. In addition to drawings, layers can contain other visual elements, such as still photographs. Layers can be blended together to combine various design aspects in real time. For example, a feature of a design developed by one design team can be stored as a layer and incorporated into another team's sketch. A multilevel undo capability allows users to backtrack and modify their work as desired. In this way, various component design concepts can be studied visually before one is finalized.

Alias developed the StudioPaint program for nontechnical users such as those in automobile styling studios. The software interface mimics traditional artists' tools like paintbrushes and palettes. However, the price tag for high-end visualization and rendering systems, such as StudioPaint, CDPS, and Advanced Visualizer, represents an investment of tens of thousands of dollars. Minimum system requirements for StudioPaint include a Silicon Graphics workstation with 64 MB of memory and a graphics subsystem.


Many traditional CAD/CAM vendors have expanded into the visualization market in order to bring lower-cost systems to their user bases. In 1990, Autodesk Inc. of Sausalito, Calif., established its Multimedia division to provide digital visualization software to users of its AutoCAD system, among others. According to Teri Felix, a product manager in Autodesk's Multimedia division, visualization is the next natural step for AutoCAD users. "Customers are driving engineers to use more sophisticated visualization tools because they want to get an idea of what the finished product will look like before the engineer goes to work," Felix said.

Two months ago Autodesk introduced its AutoVision still-rendering system that works within AutoCAD release 12. This version includes the AVE Rendering module that produces smooth shaded images of drawings. With the materials library and editor included in AutoVision, an AutoCAD user can represent a design with textured surfaces under indoor and outdoor lighting effects. The rendering information is saved as an AutoCAD DWG file.

AutoVision features a CD-ROM containing hundreds of textures and materials that can be applied. Procedural materials are generated algorithmically to create seamless wood, metallic, marble, and granite surfaces. The materials tool set in AutoVision allows users to modify materials from the existing database and to create new ones. Characteristics such as color, grain, reflectivity, transparency, and surface texture can be controlled.

For example, a sun locator shows the sun's intensity and angle at different times of the day and year. The system uses a latitude and longitude coordinate system and regional maps that let users choose from among various geographic locations. Artificial lighting is created using point, spot, and distant lighting effects. The user can create and adjust these light sources using color, intensity, fall-off, and shadowing to simulate real lighting conditions.

AutoVision can also generate photo-realistic images, although not with the interactivity possible with high-end rendering systems. However, because it is priced lower than these other systems, by $800, it is more easily available to a wider range of engineers. The software requires AutoCAD release 12 and runs on MS-DOS-based 80386 and 80486 PCs, requiring 8 MB of RAM, a VGA display, a math coprocessor, and an AutoCAD-supported pointing device.

The Mechanical Design division of Hewlett-Packard Co. in Fort Collins, Colo., has added advanced display features to its ME-30 CAD and Solid Designer solid modeling systems. Rendering capabilities available for ME-30 include ray tracing of 2-D images and radiosity (detailed 3-D imaging) functions for producing enhanced 3-D photo-realistic walk-through simulations. Up to 16 different light sources can be specified. A database includes the reflective and refractive properties for multiple types of glass and other materials. Although dynamic shading and lighting functions are available for Solid Designer, full rendering functions are not complete as of the latest 2.0 release.

Paul Hamilton, solid modeling program manager at Hewlett-Packard, said some mechanical engineers currently use the rendering functions to create representations of their designs. However, the major users tend to be industrial design firms who use these functions heavily in the work they do for clients. "Visualization software will gain popularity among engineers as the hardware becomes faster and the engineers learn to appreciate the value of photo-realistic images," Hamilton said.


The opportunity to use CAD drawings as a basis to construct photo-realistic quality images has prompted some CAD vendors to seek support from third-party software developers. Software Engineering Associates (SEA) Corp. of Newport, R.I., develops applications for users of CADDS 5 from Computervision in Bedford, Mass. While CADDS 5 contains some rendering capability in the form of its CADDShade and ImageDesign modules, SEA decided to develop a more robust system. The company developed its LightRender visualization product and is working with Computervision to integrate it tightly with CADDS 5.

The core components of LightRender are Computervision's CV-DORS ISSM and the LightWork Design applications-development system from LightWork Design Ltd. of Sheffield, U.K. The system also includes tools for generating a Motif user interface and C++ class libraries. The CV-DORS component provides access to geometries in the CADDS database for modeling purposes. The LightWork Design system was used to create most of the rendering features.

The LightRender system allows users to create photo-realistic images from CADDS 4X and CADDS 5 drawings. The system has a clipping feature, whereby only portions of the drawing currently in view are affected by the rendering functions. Clipping planes perpendicular to the view direction are used to reveal details that would otherwise be hidden. For a particular view, patterns, colors, and textures can be applied to the surface to simulate various materials. The system has planar, cylindrical, or spherical mapping of surface patterns to ensure uniformity. The appearance of light reflected from the visible surface is specified, as are any transparency features.

LightRender supports standard visualization features such as ray tracing, antialiasing, and various shading schemes. The image can be viewed either in its entirety or as if through a camera lens at a specified perspective. Natural and artificial lights and shadows are generated through five different light-source types. The background portion of the image, which is not related to the selected geometry, can be shown as a uniform color, in graduated patterns, or from a previously generated computer image or a scanned-in photograph.

LightWork's applications-development system was also used by Matra Datavision of Tewksbury, Mass., to develop the Photorealistic Rendering module for its Euclid-3 CAD/CAM system. Photorealistic Rendering is a $5000 optional module that is integrated directly into Euclid-3. Matra's implementation of the technology includes a color palette of more than 500 different tones and a library of different metals, woods, plastics, ceramics, and glasses. Surface textures can be rough, smooth, dimpled, or cast.

According to George LeBlanc, Matra's vice president of marketing and business development, photo-realism is not only important for marketing communications, but also for evaluating engineering details related to depth and perspective. "Advanced visualization tools are a natural for industrial design firms that have to communicate ideas fully to clients," LeBlanc said. He indicated that photo-realism allows users to explore the aesthetic qualities of a design in its intended setting. "It is also useful for realistically depicting parts and assemblies," he said.


Visualization systems bridge the gap between engineering and art. In creating accurate visualizations of actual products, users are helped by both a thorough understanding of the engineering behind a design and an artist's eye for color, texture, lighting, and setting. The expensive high-end rendering systems are used mostly by expert stylists. However, the more recent class of rendering systems is intended for use by the engineers that now regard a mechanical drawing as a completed job.

The rendering packages function as graphics pre- and post-processors in the product-design process, said Sukumar Ramanathan, mechanical CAD segment manager for Sun Microsystems. "Visualization systems add realism to the design of objects," he said.
COPYRIGHT 1993 American Society of Mechanical Engineers
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Title Annotation:computer-aided design
Author:Puttre, Michael
Publication:Mechanical Engineering-CIME
Article Type:Cover Story
Date:Dec 1, 1993
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