Issue: Volume: 23 Issue: 3 (March 2000)

The CAID Connection

Gray Holland is not a pitcher on any baseball team. He is an industrial designer, a principal of the San Francisco-based firm Alchemy Labs. But he likes to use a pitching analogy to describe the integration of computer-aided industrial design (CAID) and computer-aided design (CAD). In the analogy, he is a pitcher who throws a design created in his CAID system to an engineer, a catcher, who imports it into a CAD system. The reason they are playing together is to bring a new product to market.

"To make the integration work, you have to have a professional pitcher and a professional catcher," says Holland. "On our end, that means preparing design files so they work within CAD systems. But we also need people on the engineering side who understand what they are receiving."
Design Interface in Hong Kong created surfaces for this concept vehicle with tools from Unigraphics Solutions' Studio for Design, which is integrated within UG's CAD system.

Integration between CAID and CAD is desirable because it allows the industrial designer's vision to carry through to product engineering and manufacturing, ensuring that what the designer intends is what gets built. Unfortunately, the integration of these two tools has not always gone well. Even though both types of software define shapes mathematically, it has been so difficult to transfer CAID surface models to CAD solid modeling programs that many people won't even make the attempt. Says Holland, returning to his baseball analogy, "Have you ever tried throwing a ball to someone who just stands there with his arms crossed? We encounter that a lot."

Some people have managed to make CAID-CAD integration work, either through persistence or expertise with the software, or both. CAID and CAD vendors are doing their parts, too, by developing technology that better links the two types of design models. But as much as new tools can help, CAID-CAD integration is also affected by basic human issues like work styles and communication. Effective integration, it seems, will only happen when new tools are combined with new ways of thinking.

Even though CAID and CAD both define shapes mathematically, that's where the similarity ends. CAID is a tool for creative people who need "freedom to experiment with shape and form," according to Al Lopez, manager of Alias|Wavefront's design business unit. On the other hand, he says, CAD "implements the rigor and discipline of engineering."

CAID programs such as Alias|Wavefront's Studio Tools, Parametric Technology Corp.'s ICEM Surf, and SDRC's Imageware provide the kind of free-form surface modeling tools that let designers create organic forms on screen. These programs also offer extensive visualization tools such as photorealistic rendering, texture mapping, surface highlighting, and so on. Thus, they are designed to facilitate the creative process by letting users push and pull shapes and immediately visualize the effect. Engineers don't push or pull their CAD models. They position geometry precisely, often specifying exactly where something should go by typing in a number. In fact, the underlying philosophy of CAD is precise and numeric, involving variables such as clearances, tolerances, wall thicknesses, draft angles-about as far as you can get from "free form."

The other main difference between CAID and CAD is the end result. With CAID, it is a surface model; with CAD it is usually a solid model. In an ideal world, the CAID surface model is imported into a CAD system, where an engineer turns it into a solid model, then adds the features necessary to turn the conceptual design into a real, manufacturable product. But that ideal process often falls apart at the point where the surface model converts to a solid model.
A study in context: Industrial designer Gray Holland used Alias|Wavefront's Studio to match the material and color of this blender to various settings and to format the model's surfaces for accurate conversion to a CAD solid model.

One of problems is that, to a CAD system, the surface model being imported must be "water tight," which means there shouldn't be any gaps between surface patches. If there are, the CAD system can't convert the surface model to a solid. Often, though, there are gaps between the surfaces of a CAID model. (These gaps wouldn't be visible to the industrial designer; they're so minute that they don't show up on the screen. But they exist in the mathematical description of the surface patches.) A few gaps can be accommodated. CAD programs should have tools to let the engineer stitch them together. But a conceptual model can have hundreds of surface patches, each with many sides. If there are too many gaps, the engineer will throw up his hands and rightly say, "I can't use this model. It's no good."

One option when this happens is for the engineer to start from scratch and recreate a design as a solid model in the CAD system. But, not being an artist and perhaps unaware of some of the subtleties of shape, the engineer is likely to lose some of the designer's intent. Or, the engineer might try to fill in the gaps, which isn't always the best solution either. "If he fixes them in his CAD package, he ends up changing the surfaces anyway, so design intent is lost," says Dave Schmitz, manager of complex surfacing/reverse engineering at Progressive Engineering Inc., Fond du Lac, Wisconsin.

The fact that there are gaps in CAID surface models is not an indictment of CAID software. Generally, today's CAID programs are capable of creating highly precise, manufacturable surfaces. You should be able to take a well-crafted CAID surface model, run it through a CAM program, and machine the surfaces without a problem. Alias|Wavefront, for example, claims that companies do this routinely with models created in Studio.
Using Alias|Wavefront's Studio, artists at Alchemy Labs designed the shell for this glider launcher while a team of engineers used PTC's Pro/E to create the firing mechanism. The groups worked concurrently, freely sharing files between the two pro

The gap problem that occurs when CAID surfaces are transferred into CAD happens because the two programs use different "gap tolerances," which dictate how they define continuous surfaces. What the CAID program might see as one surface, the CAD program might see as two distinct surface patches based on its different definition of what constitutes a gap versus what constitutes a continuous surface. And gap tolerances aren't the only problem. The two programs also use different continuity tolerances, which define how they recognize curves. These discrepancies also cause problems in CAID-CAD integration.

Industrial designers, therefore, must make sure they know what CAD system their designs will be going into, and what their gap and continuity tolerances are. Then they must create models that meet those tolerance requirements. They must also think about how their CAID models will be translated for import into a CAD system. "It's critical that you understand what vehicle you're using to transfer the data, whether it's STEP or IGES, and which kind of IGES," says Schmitz, who is an accomplished user of both CAID and CAD. "I always use IGES 128 because the main CAD tool I use, Pro/Engineer, likes that."

Creating a CAID model that will transfer accurately to CAD is a matter of the industrial designer's craftsmanship, according to Holland, who has instituted procedures at Alchemy Labs to ensure that its designs transfer well. "Sloppy work ends up in data transfer issues," Holland says. "If the engineer who gets my design says, 'It doesn't hold water, and it's too much work to fix,' then I haven't done my job."

For their part, CAID and CAD vendors are doing what they can to help industrial designers be good pitchers. One way they're doing this is with direct translators that replace neutral file-transfer formats such as STEP and IGES. For example, Alias|Wavefront has worked with Dassault Systemes, Uni graphics Solutions, and SDRC to create what it calls "Direct Connects" between its Studio software and Catia, Uni graphics, and I-DEAS Master Series, re spectively. Rather than converting a surface model into a neutral format, a Studio user makes a simple menu pick to indicate which of these three CAD programs he wants the file exported into. Behind the scenes, the Direct Connect program formats the surface model in such a way that it is more acceptable to the CAD program than a plain STEP or IGES file.

Parametric Technology Corp. (PTC) has taken a similar approach since purchasing ICEM Surf. ICEM Surf 2000i, introduced last July, includes a direct link to Pro/Engineer. Schmitz, who formerly used IGES 128 to move ICEM Surf files into this CAD system, has tried the direct link and found it to be extremely helpful. Not only does it prepare his surface model for export into Pro/Engineer, it does so in such a way that makes the model more useful once it gets there.
PTC's ICEM Surf was used to design this Delta faucet and export gap-free surfaces into Pro/E.

"In the past, when Pro/Engineer imported a surface model that was not created in Pro/Engineer, it assigned a number to every edge, every patch side, and every corner," Schmitz explains. "As you added features to the Pro/E model, the software referenced those numbers." A hole might be placed one inch from the border of edge #1234, for example. "The software referenced the number, not the actual surface. If I changed the conceptual design and wanted to import a new surface, Pro/Engineer assigned it new numbers. So all the features that referenced the previous numbers failed."

Now, when ICEM Surf creates a file for export to Pro/Engineer, it, not the CAD program, assigns the numbers for the edges, patch sides, and so on. They are called persistent identifiers because they don't change when the surfaces are modified. "When I bring a surface model into Pro/E, it asks me what surface I'm replacing," Schmitz says. "Because the surface keeps the old numbers, everything that was related to it in the CAD model will update. It's a big improvement." PTC has also created a direct link between its other surface-modeling program, CDRS 2000i, and Pro/Engineer.

In addition to direct connections between CAID and CAD, vendors offer a few other tools to help automate the preparation of surface models for CAD. Alias|Wavefront, for example, includes "presets" in Studio that let the industrial designer specify, before building a model, which CAD program will be reading it. "The software sets the build tolerances to the appropriate level for the target CAD system," explains Lopez. "Designers also use the software's Stitch tool to sew up the model. It tells them whether they achieved all those tolerance levels."

The typical process for an industrial designer is to create complex networks of curves, then individual surface patches, then establish continuity between the patches. SDRC's Imageware tool set includes Surface Wizard, which is said to free the designer from this laborious process and automatically ensure continuity between patches. According to SDRC, Surface Wizard requires the user to select the corners of the patch structure. The selected patch structure can have any number of surfaces, including a mixture of patches consisting of three to seven sides. Wizard then automatically creates a multi-surface NURBS model with continuity between all patches.

Most of the efforts at CAID-CAD integration involve communication between two fundamentally different types of software. Even though the same vendor owns both the CAID and CAD programs in the case of PTC and SDRC, their CAID software was purchased, not developed in-house, therefore complicating the integration with CAD. For a different approach to solving the CAID-CAD integration problem, users can now opt to buy CAID and CAD programs built on the same geometric modeling kernel from Unigraphics Solutions. This company recently announced a new product for industrial designers called Studio for Design that is built on the Parasolid kernel, the foundation of the company's Unigraphics CAD system.
Innodesign in Palo Alto helped preserve the artistic intent of this radical new bike by creating engineering-ready surface models using UG's Studio for Design.

"All the work is done in one environment where it is possible to create industrial designs and then use Unigraphics to add detail and create an engineering model," says Mike Rebrukh, marketing manager at Unigraphics Solutions. The main benefit is the ability to handle changes to the conceptual design without having to recreate the CAD model, he says. "You can make a change in the conceptual design it automatically propagates to the engineering model."

Even with all this technological assistance, there is a cultural component to the integration of CAID and CAD that can't be overlooked. When Holland of Alchemy Labs referred to trying to pitch a ball to someone with his arms crossed, he was referring to one of the cultural issues that comes into play. "Until now, the engineer has been the sole custodian of CAD development, and a lot of engineers see CAID as a threat to their existence," says Holland. "He may not be willing to do much to catch the ball. If we're super good, we might be able to lob it and make it lodge into his arms. That's what we have to do sometimes. Or we have to get the umpire or head coach to say, 'You're going to catch this ball whether you like it or not.' A lot of times engineers are very resistant until they realize that by letting us create the surfaces, they are now free to do what they do best."

Effective integration between CAID and CAD, therefore, requires more than tools that manage technical details like gap tolerances and file-transfer formats. It requires willingness on the part of industrial designers to take the extra steps and create models that meet the requirements of CAD. It also takes willingness on the part of engineers to accept CAID, to bring surface models in and work with them, even sew them up a bit if necessary. Many of the tools are here now. But people must be willing to use them. It's time to play ball.

Caren Potter is a contributing editor of Computer Graphics World. She can be reached at

Parametric Technology Corp.
Waltham, MA

Milford, OH

Toronto, Canada

Unigraphics Solutions
St. Louis, MO