The Interoperability Challenge

The data import process in Inventor's Construction Environment requires a closer look

I just returned from Autodesk University 2006 in Las Vegas, after spending some quality time with well over 7,000 fellow attendees. Although Las Vegas is not my favorite city to visit, it's always great getting reacquainted with my peers, Autodesk employees and end users of the various Autodesk mechanical products.

This time around, I did something I had never done before at AU: I taught a class. My topic was IGES and STEP data translation in the Construction Environment in Autodesk Inventor 11. It was, in other words, an attempt to address and resolve interoperability issues with Inventor.

I explained to the class that although I don't do much design work these days, I do have occasion to transfer IGES and STEP data between Inventor, SolidWorks and Pro/ENGINEER. This is done mostly for benchmarking and comparative analysis, but I do a fair amount of it (with varying degrees of success). I have to say that the data import process in Inventor's Construction Environment -- while not perfect -- is well implemented, so let's take a peek at it.

A Little History

The Construction Environment has always been a "staging area" for purifying data, ensuring that what comes out of it can be used in Inventor when it is promoted to the Part Environment and used. The goal is to make the data promoted to the Part Environment cleaner than the data that was imported, even if it will only be used as reference data for modeling.

Looking back a few releases, Inventor 5 implemented the "data basket," where imported data could be stored, but which was not a true data manipulation environment. Inventor 6 introduced the beginning of what is now known as the Construction Environment with a few commands for manipulating the data, such as Stitch and Promote.

Today, the Construction Environment can handle IGES, STEP and SAT files. In my experience, IGES is used primarily for surfaces. STEP is used primarily for solids and assemblies, although I’m starting to see more surfacing data in STEP files. Inventor 11 introduced the ability for exporting STEP surfaces, so this will likely contribute to the increased use of STEP in the future. Personally, I deal with IGES data almost exclusively these days, but I suspect that STEP will enter the fray in a bigger way as time goes on, because it seems to have more support behind it for the long haul.

The goal of the Construction Environment has always been to provide a non-parametric (non-history-based) place for importing and manipulating design data (such as surfaces, wires, etc.) without incurring the penalty of dealing with parameters. In short, the Construction Environment is a non-parametric, preprocessing space for IGES and STEP data to be used in Inventor. Although the basic process for using the Construction Environment isn't as straightforward as it could be (or probably will be eventually), it's reasonably easy to comprehend with some practice.

The Basic Process

Although there are other possible workflows, we'll briefly discuss one that consists of the following basic steps within Inventor 11's Construction Environment:

• Import the data
• Analyze the quality of the data
• Repair the data so that it can be promoted and used in Inventor's Part Environment
• Promote the data (once it has attained a sufficient level of quality) to the Part Environment, and use it as a standalone solid part or as a component in an assembly.

One of the most common problems that occurs when importing data is gaps between surfaces, which render them unusable as parts. Analyzing and filling these gaps is a challenging translation task, and is addressed by Inventor 11’s Construction Environment. Again, although there are a number of ways to fill gaps, probably the two most common methods are the Boundary Patch and Boundary Trim commands. What follows is a technique using the boundary patch command for filling gaps in imported data (in this case, IGES).

Filling gaps in data. After you import the data, perform an analysis and quality check on all surfaces before stitching to minimize or prevent problems later in the process. When data is imported, an associated translation report is generated that indicates the degree of success, as well as the problems the application encountered. I like this report, but wish it was more descriptive with regard to the problem areas and where they are located. Many problem issues, such as "bad" or "dirty" geometry, can be found and fixed from within this quality check tool.

Next, stitch all surfaces with the default maximum tolerance or specify another tolerance. Note that after stitching the surface model, some edges are still open with gaps and are red in color.

The gap, enclosed and bounded by open edges, is shown in red.

To fill the gap, increase the maximum tolerance and stitch the surfaces again. This results in a solid that can be promoted and used in the Part Environment. However, just increasing the maximum tolerance often fails to produce the results that you want. It’s important to remember that gaps should be filled before stitching. The Construction Environment has several tools for filling gaps, such as boundary patches.

Promote the stitched surface with the gap to the Part Environment. In the Part Environment, use the boundary patch command to fill the gap (usually defined as a boundary loop with edges) with a new surface. Copy the original surface and the newly created boundary patch back to the Construction Environment, and again use the Stitch command to produce a solid. Finally, promote the newly created solid to Inventor's Part Environment, where it can be used and edited like any other Inventor part, or as a new assembly component.

Although these steps may sound simple, they can be challenge; but, like most tasks, they get easier with practice. In upcoming releases of Inventor, I expect to see the Construction Environment become not only more capable, but also more straightforward, and therefore easier to use.

Interoperability Dilemma

The time and effort that has been devoted to data import and translation is not unique to Inventor's Construction Environment. As a matter of fact, virtually all of the major mechanical CAD vendors grapple with the ongoing interoperability dilemma. They all realize that interoperability and the many problems associated with it are not going away anytime soon, so they bite the bullet and bravely carry on -- it's business as usual. All of these issues combined will keep Autodesk Inventor's Construction Environment relevant for quite some time.