Data Migration—Getting from There to Here
When it comes to data migration, there are two main scenarios you usually face: Someone sends you a file containing data you need to incorporate into your current project or you’ve just upgraded your CAD software to a new program and you need to migrate your own legacy data. There is no need to expect the worst; the issues with using data from multiple sources can be intimidating, but it’s rather common in today’s engineering workflows. Chances are, you will not only be able to import all that data, but actually make full use of it.
In this world of corporate takeovers, online parts catalogs and global collaboration, having to use someone else’s 3D models is inevitable. The nice thing is that you probably have all the right tools already. The days of a CAD program not equipped with translators are thankfully long gone. Software vendors used to make you pay extra for such features, but today’s CAD market expectations are much different, no doubt driven by the prevalence of file formats on most modern projects of any significant scope. Nowadays, if your software doesn’t open foreign files directly, it can usually import a long list of file formats at the very least (see Figure 1).
Figure 1. Most modern CAD software comes with the ability to open models from many recognized formats. (All images courtesy of the author.)
During the Apollo moon missions, the scrubbers used to remove carbon dioxide from the air in the Command Module used square filters. The filters in the Lunar Module were round. Although they performed the exact same functions, they were by their very nature incompatible. If you ask five people to do the same job, you’re going to get five different approaches. People are creative like that. So, it should come as no surprise that software companies don’t all do things the same.
Whether you inherited legacy data from a company that was purchased or you created the data in software you no longer use, you can’t afford to just redo everything. The originating program and your program probably won’t use the same file formats. Translating data from one program to the next is not trivial. The feature construction and underlying math kernel may be very different, yet they all describe the same thing. Little differences like that can quickly add up to a lot of confusion with translation software. If you’re going to translate, make sure to clean up your geometry after the fact. If you don’t have exact intersections, instead of a closed 3D volume (solid), you could end up with an open loop that can only result in a surface (at best).
What do you do if all you’ve got is a 2D drawing? You can still use it. You will need to choose whether to leave it as 2D or build a new 3D model from it. Imported 2D geometry can be used just like native geometry to create 3D models. (Be careful when using 2D geometry. Some users in the old days did not make very consistent use of trims and snaps, instead eyeballing where lines would end. This can leave you with sketches that won’t sweep or extrude correctly. See Figure 2.)
Figure 2. Make sure all ends meet or you may not get the results you are looking for.
Paper drawings represent both problems and opportunities — problems in that they do not exist in the CAD world, and opportunities because you have a good excuse to build the part(s) from scratch. This is an opportunity because you will only truly get to know the details of your models by getting intimate with them. Many things can result from this. You could discover errors in the design or execution, or you could come up with new ways of doing things — both of which could save the company big time. If you don’t have that kind of time, you could always just scan your paper drawings and use the bitmaps. You’ll need image-editing software to make any changes, and other than describing the part(s), there will be no further functionality. Many companies do this and are perfectly satisfied. (There’s something for everyone.)
Of course, importing someone else’s models can be problematic. Sure, it can save all kinds of time and effort. But that depends on the model. If you need a screw, for instance, you can go out to a vendor’s website and download a model. Most websites offer several file formats to choose from. But not all are fully detailed. Some might not include the screw thread. While this might save in file size and performance, if you need those details, you are out of luck. Also, some models you can find out there aren’t very accurate. Say you’re looking for an electric motor. Some models will only depict what you can see, omitting anything hidden within the housing. There is a school of thought that says, “Just represent the part in the least complicated way.” That might work for finite element analysis, but it’s not always wise for good product design. In most cases, accurate CAD data is the cornerstone of any functionality you might want down the road. And in today’s industry, there is a lot of downstream application.
What do you get when you import foreign data? Either 2D or 3D geometry. You won’t typically get separate features in your feature design tree (see Figure 3). You’ll likely only see an “imported body.” You can still use it. It just won’t be as easily changeable (though that’s not too hard). There are many tools available that allow you to use that geometry. There are feature recognizers that use the topology of the model faces to make programmed guesses as to how it can be made. For instance, a cylindrical projection can be made by extruding a circle or sweeping it. The software can pick one and create what it needs to turn the geometry into a parameterized feature.
Figure 3. Instead of discretely editable features, importing data will generally result in static, unparameterized models.
Data migration is an important and useful activity. It allows existing data to be reused and continue to remain valuable. After all, existing data is a time and money investment. Someone paid to create it, and it would be a waste indeed to trash it or have to recreate it when there is a better way to save it. Besides, data migration is pretty easy nowadays. So, there’s really no excuse for not making use of what you have on hand.
About the Author
Michael Hudspeth has been a designer for two decades, a lifelong artist, an avid model builder and author (specializing in science fiction). He, his wife, two daughters and one too many cats thrive in the great American heartland, just outside of St. Louis, Missouri.