File Sharing/Publishing

Barriers to Model Exchange

11 Apr, 2004 By: Don LaCourse

Why is it so difficult to send data from one CAD system to another?


Reverse Engineering and
CAD Translators
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Figures 1–5 illustrate reverse engineering, a nontraditional method of model exchange. If you are interested in reverse engineering, these vendors offer additional options:

In addition, the following are some of the companies that develop CAD translators:

WOULDN'T IT BE NICE if we all used the same MCAD application-and that it had all of the bells and whistles found in each application available today? Everyone could send each other 3D models without worrying about losing data. Everyone could collaborate using the original master model. Everyone could benefit from each other's design intent. Wouldn't that be nice?

Ok, you can wake up now! If you're one of those rare individuals who exchanges 3D data only with partners that have your same system, you can go back to sleep. For the rest of us, this month's topic, model exchange, is one I enjoy talking about because it causes so much aggravation for MCAD operators and administrators. I don't like to see us aggravated, but I do like to take every opportunity to point out the problem and dig for solutions.

This year, I've focused on topics using one mechanical CAD program as an example and asking the developer to respond to various questions. This month, we ask Bob Fischer, vice president of sales and marketing at VX Corp., the tough questions. This should be interesting.

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Figure 1. Increased interest in reverse engineering has encouraged VX to enhance its Class A surfacing to incorporate tools that create 3D models from scanned data and point clouds.

Q: Why has there been such a problem moving 3D CAD data from one system to another?
A: I think it's a question of differing objectives on the part of the people who create and use 3D data. For example, industrial designers are typically consumed with issues such as design aesthetics or ergonomics and have little or no concern for production and part manufacturability. Industrial designers are artists intent on creating beautiful, marketable products, and as artists don't want to be concerned with issues such as tolerances.

The downstream moldmaker faces different challenges. Moldmakers must take a 3D part and create a whole new set of 3D models. Their core objectives revolve around creating efficient molds that produce thousands of parts that are in tolerance.

While the moldmaker worries about draft, core and cavity separation, and parting lines, a CNC programmer is more worried about being able to manufacture the resulting 3D parts. Often, manufacturing models lack suitable features for automatic tool selection, or 3D models don't meet tolerance standards.

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Figure 2. To assist in creating accurate 3D models, VX provides built-in surfacing and moldmaking analysis tools.

Q: What are some of the difficulties that developers have overcome (or addressed) in recent years?
A: To meet the needs of end-to-end customers (designers, moldmakers, and CNC programmers alike), application developers have taken a proactive stance by developing extensive suites of healing tools for working with 3D models. This enables all users to work with and heal imprecise data.

The hybrid-modeling environment is one way that users can overcome some of the difficulties in model exchange. Typically, solid modelers require a closed solid to perform most 3D functions such as moldmaking and manufacturing. Hybrid modelers let you work with open solids, thereby dramatically increasing their flexibility and efficiency.

Another important translation development is ongoing improvements in data recognition and fault tolerance. Although geometry can be automatically healed as it is read in, that occurs only after the data format is repaired.

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Figure 3. Unlike many solids-only systems, the VX Overdrive kernel fully integrates mold and die tools that work with all forms of imported geometry, not just closed solids.

Q: What are current model translation trends from the perspective of CAD software developers?
A: There seems to be a movement to direct translation. Customers are shackled to a CAD system if they can't convert their part libraries to another system with a high degree of accuracy. This conversion involves geometric accuracy. Users want full feature transfers, undo and redo, history, annotations, and so on. With a direct translator, the customer has the best chance of converting data.

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Figure 4. VX provides direct import of parts from popular online and third-party libraries to assist in assembly modeling. VX Burst Technology speeds display and loading of massive models and large assemblies.

Q: What are the challenges yet to be overcome?
A: The industry needs better tools to translate features, design history, and intent. A few developers are attempting to fill the gap, but there's still a long way to go.

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Figure 5. Models from scan data and point clouds are fully compatible with VX CAM, a machining module built into VX from day one.

Q: What nontraditional methods are being used to exchange 3D modeling data?
A: There seems to be an active resurgence and interest in reverse engineering. We've experienced growing interest in our ScanShape tools, especially from companies that want to recreate 3D digital models from parts that weren't designed using CAD technology. An additional reverse-engineering trend is the high-tech world of 3D printing using yet another neutral file format, STL.

Articles & Online Resources.
Tips for translation
Yes, it would be nice if we all lived in that perfect world where model exchange hassles were a thing of the past. However, this problem has been with us for at least 20 years, and I expect it to continue. If you're having model exchange problems, look for a good direct translator between you and your exchange partners. If you use one of the neutral formats, such as IGES or STEP, perform extensive testing between the CAD systems. If you are one of those rare individuals who only exchanges 3D data with partners that have your same system, wake up now and go back to work. The rest of us will keep on dreaming!

A special thanks to Bob Fisher of VX Corp. for sharing his expertise with us this month.

Roots of the Problem.
Why has there been such a problem moving 3D CAD data from one system to another? The translation experts at VX listed these additional reasons:
  • The IGES standard is a couple of hundred pages long and has existed under strict scrutiny for more than three decades. VDA-FS weighs in at a dozen or so pages. STEP documentation is huge—as in a truckload. These standards are open to interpretation, and developers interpret them differently. And there is always the opportunity for programming errors—dare I say bugs!
  • The purpose of a translation standard is to provide a pipeline by which competing products can communicate without giving away trade secrets. This is very effective because it minimizes the translation burden. Instead of an n-by-n translator, one for each pair of applications, the pipeline is composed of a handful of accepted translation types.
  • VX is making it easier to export in STEP by providing free-use STEP tools at www.vx.com/step/ that repair the documentation and make it easier to implement. The documents are hyperlinked with encoding generators and inheritance mappers to ease the implementation burden.
  • This brings us to flavored outputs that target individual CAD systems, part of the movement back to direct translation between systems. This movement is driven by the desire to transfer more complex information, such as part history regeneration, between systems.
  • With these elements muddying the waters, we get to the fundamental problems of data transfer: customers want to make a roundtrip translation without losing any of the benefits of the native system, such as undo, redo, and feature recognition.
  • The root of all translation evil is tolerance. Tolerance defines when two different points are considered close enough to define the same point. Complication is magnified by magnitudes when curve tolerance and surface tolerance are thrown into the mix.


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