MCAD Modeling Methods-What Do You Do With Legacy Data?1 Jul, 2006 By: IDSA ,Mike Hudspeth
Changing from one format to another doesn't mean losing old work files
The only constant is change. It's not an original concept, but how many things in our jobs stay the same year in and year out? Statistics show we will change what we do as many as six times in our lives. With all that change, how can we expect our design data to stay in the same format forever? But there's no need to lose out when we transition to a newer technology. We can still get plenty of use out of our legacy data. We just need to know what to do.
In the old days, drawings were done with pencil and ink on a drawing board. In the course of your daily business you could create beautiful works of art. One place I worked acquired a bunch of linen architectural drawings from the early 1900s and used them for wallpaper. (I sat under a gargoyle that stared at me.) The downside to manual drawings was that once you laid down your initial view, the rest of the drawing would be based on it. If you ran out of room, you were in trouble. If changes needed to be made, you had a lot of erasing to do. And if you made a mistake, there was no Undo command. Add to that the difficulty of visualizing what each orthographic view should look like and what features would be visible, and you can see how difficult it was.
Today we have 3D solid modeling. But when we decide to adopt a 3D modeling system, will we lose all the work that went on before, whether manual or 2D CAD drawings? No. There are many ways to maintain the value of our legacy designs.
Paper to CAD
Scanning 2D board drawings is a fast and simple way to bring designs into the digital realm. You can outsource the task or buy a scanner and do it yourself. A large-format scanner big enough to digitize D- and E-size drawings isn't cheap (see Cadalyst's April scanner survey at www.cadalyst.com/0406scanners/). You'll also spend a good chunk of really boring time (looks like a job for Super Temp!) actually doing the scanning. You'll end up with bit-map, or raster, files in whatever format you choose (figure 1). At that point, you can choose to keep the drawings in raster form and edit them with a bit-map editor (for example, Adobe Photoshop, Corel PHOTO-PAINT or even Windows Paint Brush). Or you can turn them into vector files.
Figure 1. With 2D scans, it really is garbage in, garbage out. Unless your drawings are in fairly pristine condition, you'll need to do a bit of cleanup.
A bit-map is a pixel-by-pixel file. It has no sense of direction. All it knows is this pixel is black, and that one is yellow. A vector format file (such as CGM or DXF) has a lot more built-in intelligence. Instead of pixels, it deals with lines and arcs, entities that have direction and dimension. To edit a bit-map line, you must change each pixel. To edit a vector line, you merely change one of the ends.
If you want to get terribly technical, AutoCAD would classify as a vector editor (so would CorelDRAW and Adobe Illustrator, for that matter). Raster-to-vector converters such as CorelTRACE examine a selected bit-map file and put edges to each discrete color. If you send it a black-and-white bit-map, the job will be easier. The downside to these programs is that frequently you end up with an amorphous shape rather than a line (figure 2) because every printed line, no matter how thin, has a width. Vectorizers see that, recognize it as a perimeter and trace around it. This function can be a good thing, though, because you won't have to worry about the relationships between lines changing because you changed the scale of the image. The programs also can be set to interpolate a line by finding the exact center between the sides of a line perimeter.
Figure 2. When you vectorize a line from a bit-map, you most often end up with a perimeter rather than a single line. This outcome makes editing a challenge.
Part to CAD
What do you do if your legacy data is a 3D part? Suppose there's a fire or other disaster. You may not have off-site duplicates (you always should have off-site duplicates, though). If you have a part, you can do a 3D scan of it. This scanning sounds really cool, but in actual practice you need to be pretty careful. A lot of things can combine to make 3D scanned data next to useless (figure 3). See the January 2006 "MCAD Modeling Methods," www.cadalyst.com/0106mcad/, for a more in-depth discussion of 3D scanning.
Figure 3. 3D scans can be marvelous things. They can capture minute detail and bring it into a form you can use for modeling. Sometimes you must be careful because they don't always have the resolution you want.
The inherent limitations of 3D scanners can make some parts difficult to use. Do some research first, or better yet, ask your scanning vendor for a demo scan of one of your parts. When you get your 3D scan, it most likely will come as point clouds or surfaces. Either way, you can use the information to build very nice models of your products.
CAD to CAD
The $1 billion problem. NIST (National Institute for Standards and Technology) estimated that issues related to CAD interoperability cost Ford, General Motors and Daimler/Chrysler more than $1 billion in one year. Imagine what that number would be for all U.S. companies combined.
Obsolete CAD programs can become a huge limitation. When what you have no longer can keep up with what you want to do, it's time to look for something new. If you stay with a newer version of what you currently have, you'll likely have little trouble using your old data files. If you go from 2D to 3D, however, you'll probably end up with a new application. So what happens to your legacy files? You have essentially four options: chuck 'em and start over, keep a seat or two of your old software around as long as you can, get a viewer or translator that reads the files or rebuild each file as needed.
Viewers vs. Translators. In this corner, programs that look into all kinds of file formats so users can extract useful data such as measurements and visualizations; in the other corner, translators that transform disparate data files into something that can be imported into newer or at least different programs. Both types are useful, but I give the fight to the translators because they give users more value. Viewers are good for just looking, but if you want to touch and change, you need to go with the translators.
All good 3D modelers come with some kind of translation capability. If your legacy data isn't in a format that you can translate into your current system, investigate whether translation is possible. Many companies, for a nominal fee, will translate everything you've got. These services are a good way to go because they do these translations day in and day out. They know what they're doing, and they'll usually do it faster than you can. Not everything migrates easily—sometimes you end up a few entities short. Thoroughly check everything you get.
As I mentioned earlier, sometimes changing programs is a great opportunity to go to 3D. There are many ways to make the transition without losing your 2D data. Programs such as SolidWorks and Solid Edge now both read and edit AutoCAD files. You can bring your old files into these programs and maintain them there. But the fun doesn't stop with that! You can open your flat, 2D drawings and use them to generate 3D solids. You open the old drawing and tell Solid Edge which view is the front, top, side, etc. Then Solid Edge puts those views on corresponding planes (figure 4). Once they're there, you just start modeling.
Figure 4. In Solid Edge, you can take an AutoCAD drawing and use it to build a 3D solid model—that is, if everything lines up correctly.
Of course, sometimes you can't work from a drafted drawing. Sometimes all you have is a photo or a hand drawing. NX 4 from UGS lets you sketch with bit-maps. Much like the procedure above, you can apply your bit-maps right to planes and use them to sketch out the shapes you want (figure 5).
Figure 5. NX 4 lets you import bit-maps into your sketching environment and use them to trace the shapes you want.
Oldies but Goodies
Just because you might change software programs someday doesn't mean what you do today will be rendered useless. You can continue to work with your hard-earned and expensive data. Don't be afraid to look at new things. The old stuff still will be there for you.
Mike Hudspeth, IDSA, is an industrial designer, artist and author based in St. Louis, Missouri.
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