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Speaking Different Languages PUBLIC ACCESS

Exchanging Designs Between CAD Programs has Never Been Easy and is Often Laborious.

[+] Author Notes

Associate Editor

Mechanical Engineering 123(02), 53-55 (Feb 01, 2001) (3 pages) doi:10.1115/1.2001-FEB-3

This article illustrates the importance of interoperability between computer-aided design (CAD), computer-aided manufacturing (CAM), and computer-aided engineering (CAE) software. Interoperability is an intricate concept, rife with accusation and blame-laying, and dependent on the unseen algorithms and mathematical equations that drive the lines and geometries CAD users see on screen. At the Daratech 2000 summit, a panel of technology users and technology vendors worked together to draft what was called a symposium communique that challenged suppliers to cooperate more with one another to move toward interoperability. The communique calls the interoperability issue one of the most troublesome aspects of CAD, CAM, and CAE usage. PTC in Waltham, MA, has released Associate Topology Bus, a tool that thy company says helps engineers share data between systems by allowing them to exchange geometry as well as what the company calls design-intent, between systems. Autodesk of San Rafael, California, offers interoperable features as what it calls DWG linking between its AutoCAD software and its 3D Studio Viz, a system used by architects. Its Mechanical Desktop software can read printed circuit board data in intermediate data format (IDF) and convert it to AutoCAD objects suitable for further mechanical design and manufacturing applications.

Pity the poor engineers who work on the same projects but use different computer-aided design systems. For them, passing information back and forth can sometimes be a logistical nightmare because their CAD systems don't share the same internal data formats and, therefore, can't communicate easily. Many engineers find themselves spending a great deal of time translating CAD designs, and losing information in the process.

The key word here is "interoperability." In engineering computerese, it means the ability for CAD, computer-aided manufacturing, and computer-aided engineering information to be read universally across programs.

In an ideally interoperable world, an engineer could create a design using CATIA software, for example, and send it to suppliers who can open it, read it, and mark it up, regardless of the software their company uses. They would be assured that any changes they might make would show up on the engineer's CATIA model.

But that's not usually the way things work, according to Bruce Jenkins, vice president of Daratech, a Cambridge, Mass., market research and technology assessment firm that specializes in CAD, CAM, CAE, and other systems used by engineering companies.

"It's difficult for engineers because their technologies don't work well together:' Jenkins said.

Interoperability is an intricate concept, rife with accusation and blame-laying, and dependent on the unseen algorithms and mathematical equations that drive the lines and geometries CAD users see on screen. "You could write a book about the issue," Jenkins said.

Sharing CAD files is a major issue in today's engineering workplace, where engineers are often linked to the entire supply chain via computer networks that can pass digital images back and forth for review with everyone from managers to marketers, manufacturers, or suppliers. Many times, all these people open the file on different CAD systems because it's difficult, if not impossible, to decree that all users standardize on one system.

A company that signs on as an engineering supplier might already have a CAD system in place, for example, and be loath to implement another one. Also, different CAD packages work best in different applications. A manufacturing company might choose a package suited to its needs. A supplier might select a low-end system used mainly to view images. An engineering company might implement a high-end system.

Add to this the complication that most companies use more than one internal CAD system to meet their varied needs, and you get a clearer picture of why engineers feel it's necessary for these systems to work together smoothly.

The reason these systems can't read each other's files , Jenkins said, lies with a number of technical problems that stem from the different internal data formats of CAD systems. But the software vendors themselves are not without blame, he added.

"It just so happens that companies build their systems in splendid isolation, each with a view toward making their system give as much function and performance as it can," he said. "Different developers took different tacks to that."

And those different tacks result in systems dependent on algorithms that vendors are often unwilling to share or make known.

"It comes down to that, traditionally, software vendors have seen closed and proprietary data structures as a key to control and to retaining ownership of a customer base," Jenkins said.

Unigraphics Solutions of St. Louis has published a white paper on the interoperability issue that makes the same point. For competitive reasons, CAD vendors simply aren't willing to reveal their algorithms, the white paper says, and it adds, "That makes it impossible to transfer both files and codes among unlike systems, whether it's high-end to high-end or mid-range to high-end."

At the Daratech 2000 summit last March, a panel of technology users and technology vendors worked together to draft what was called a symposium communique that challenged suppliers to cooperate more with one another to move toward interoperability.

The communique calls the interoperability issue one of the most troublesome aspects of CAD, CAM, and CAE usage.

Unigraphics users can pass untranslated models to Solid Edge via special software.

Grahic Jump LocationUnigraphics users can pass untranslated models to Solid Edge via special software.

In a perfect world, CAD designers could share models freely across CAD systems.

Grahic Jump LocationIn a perfect world, CAD designers could share models freely across CAD systems.

To be fair, engineers who want to share their data across different systems can first translate their information into a standard form that can be read across systems, often the initial graphics exchange standard (IGES) or the standard for the exchange of product data (STEP) . Jenkins has pinpointed a main problem with translation, however.

"There's the loss of so much modeling data ," he said.

The Unigraphics Solutions white paper said the file transfer formats just don't go far enough. " IGES is the lowest common denominator, and when you use the lowest common denominator, you lose a lot," the paper stated. "That might be acceptable in some disciplines, but it's rarely acceptable when engineers are trading information about solid models."

STEP is ISO, the international standards-setting body's choice as an across-the-board replacement for disparate file transfer formats, which include data exchange format (DXF), IGES, and drawing Web format (DWF) . But, while STEP offers significant improvements over IGES, it isn't really a solution, according to Jenkins.

The translation programs have the same problems as human translators. Sometimes, there just isn't a one-to-one correlation between words or, in the case of CAD systems, pieces of geometric intelligence.

"You'd think a fillet is a fillet, but the way the geometry is described in one CAD system won't have a direct correlation with another system," Jenkins said. So important information about the fillet would be lost in the translation. It would show up, when translated, as incomplete.

In such cases, information about the fillet might be attached to the translation as a note that says, in effect: "This is what the fillet looks like."

"Certainly a note is not something that a CAM package can read," Jenkins said. "Someone has to interpret it."

And therein lies the rub. Translated models have to be opened by a user and gone over for notes and discrepancies before they can be dealt with in the user's system. And then they have to be translated back to a standard format to be sent anywhere.

Again, much pertinent information can be lost in this translation. It's also time-consuming and takes engineers away from other important tasks they might be doing.

And there's another issue as well. IGES and STEP standards have to evolve as fast as today's engineering technologies are evolving. And a standards committee can't keep up.

"In the beginning, there was two-dimensional drafting. And IGES supported it," Jenkins said. "Then came three-dimensional modeling, and standards organizations struggled to implement IGES standards for 3-D. And developers struggled to implement those standards at the same time they were going beyond 3-D modeling to feature-based development, and the standards committee had to come up with standards definitions for the new stuff."

In other words, the translators always lag behind the stepped-up, constantly evolving pace of software vendors' development simply because the standards-setting committee has to react after new tools have been developed. And new standards certainly can't be set and implemented overnight.

Software Vendors Reply

For their part, many CAD vendors say they are doing their best-short of giving away trade secrets-to acconml0date their users when it comes to interoperability. PTC in Waltham Mass., for example, has released Associate Topology Bus, a tool that thy company says helps engineers share data between systems by allowing them to exchange geometry as well as what the company calls design-intent, between systems. That is, in addition to geometric data , the exchanged data includes information on where adjacent parts and lines connect.

A formal statement from PTC said that promoting collaboration via an open exchange of data between Pro/ Engineer-the company's CAD product-and other CAD systems is at the heart of PTC's commitment to its customers.

Steven Walske, PTC's chief executive officer, said that customers need to drive their vendors to force inter operability.

Unigraphics Solutions said that transmitting files via STEP across systems that share the company's Parasolid kernel is especially easy, and users need not fear data loss. Parasolid licensees include ANSYS, Mechanical Dynamics, MSC.Software, PTC, and SolidWorks . And Unigraphics Solutions offers what it calls associative embedding, which allows interoperability between Unigraphics the company's higher-end CAD system, and Solid Edge, the company's mid-range CAD system.

Autodesk of San Rafael, Calif., offers such interoperable features as what it calls DWG linking between its AutoCAD soft\¥are and its 3D Studio Viz, a system used by architects . Its Mechanical Desktop software has the ability to read printed circuit board data in intermediate data format (IDF) and convert it to AutoCAD objects suitable for further mechanical design and manufacturing applications.

The methods still require some translation between formats, however. And they often link two specific software packages. They can't be used to link the user's system to any system that the user happens to be exchanging data with at that moment.

Also, Jenkins said, vendors could do more. A third-party software developer could write a translation system that goes between two CAD packages. But vendors seldom allow full access of their data to third-party vendors, he said.

Daratech's view is that the CAD vendors could and should grant more information about their software, Jenkins said.

Meanwhile, Daratech has its eye on a company that says it will provide substantial interoperability with its first product, scheduled for release this summer. The company, Proficiency of Marlborough, Mass. , won't say a lot about its product, called the Proficiency Collaboration Gateway, although Jenkins said he has seen demonstrations.

Building a technology that moves models from one CAD system to another wasn't impossible, as had sometimes been thought, said Michael Jannery, the company's vice president of marketing. But it was very hard and time-consuming.

"We had 75 people with Ph.D.'s in mathematics and geometry working on this thing for a year," he said.

Proficiency claims that its product can pass information between two vendors' CAD systems without the need for IGES, STEP, or other translation. Users don't have to translate designs laboriously or rely on someone at the other end to translate them before opening the design.

Jenkins said a demonstration offered translations that were more than 80 percent complete. That is, 20 percent of the file needs to be interpreted or wasn't perfectly translated when it was sent between design systems.

For his part, Jenkins is withholding judgment until the product is released and will be looking to see how it deals with surface modeling. This has traditionally been a sticking point in terms of interoperability because of the dense mathematical equations that power the surface models.

"The mapping of solid models from one system to another is complex, but then there 's the added complexity in mapping one system's surface model to another due to the nature of mathematical formations that make that transaction particularly hairy," Jenkins said.

But if the Proficiency product performs as the company says, it should take interoperability to another level, he added.

Jannery, of course, promises that expectations will be met.

Until the time Proficiency proves itself or comes up short, however, engineers everywhere are still saddled with being the creators, interpreters, and translators of the work they design.

Frequently, much pertinent design information is lost in IGES or STEP translation.

Grahic Jump LocationFrequently, much pertinent design information is lost in IGES or STEP translation.

Copyright © 2001 by ASME
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