Plotting in style: The face-off between named and color-dependent plot styles.31 Mar, 2003 By: Mark Middlebrook
Though the official buzz at Autodesk University in December was about keeping CAD data digital, most of us continue to fuss with plotting to paper. Paper remains the preferred medium in many situations for all kinds of historical, practical, and legal reasons. I love the maxim "Never send a tree to do an electron's job," but until we train electrons to do all of the jobs that paper currently accomplishes, we can continue to improve the quality and consistency of our printed drawings.
AESTHETICS OF PLOTTED DRAWINGS
Manual drafting veterans often complain that CAD drawings don't look as good as the drawings they used to create by hand. Too "flat," too cartoonish, and inconsistent are common refrains. These complaints are not just the whining of old-timers. Good manual drafters were justifiably proud of their drawings' appearance. They focused on making finished bluelines look sharp and read well.
When computers and CAD software got into the act, CAD drafters focused on the screen image and paid less attention to the plotted output. In the early days, manual-drafters-turned-CAD-users struggled with a new way of making drawings and didn't have as much time to make them look good. By the time CAD became commonplace, a new crop of CAD users had grown up without the benefit of learning how to make good-looking drawings on paper.
There's no reason CAD drawings can't look as good as manual drawings. It's a matter of understanding the look you're after and caring enough to want to achieve it.
POST-RELEASE 14 PLOTTING POSSIBILITIES
AutoCAD 2000 introduced a host of new plotting possibilities (along with a fair amount of plotting confusion!): multiple paper space layouts, object lineweights, two mutually exclusive kinds of plot styles, and plot settings saved with each drawing tab. Four years and two major upgrades later, most companies continue to plot pretty much as they did in AutoCAD Release 14-that is, by mapping the screen color of objects to plotted lineweights. It's instructive to investigate why that is and whether the situation might change in the future.
Starting with AutoCAD 2000, you can choose among three basic methods for showing plotted lines with different lineweights:
Color-dependent plot style method. Assign colors to layers and/or objects, and then use a color-dependent plot style table (CTB file) to map the colors to plotted lineweights. This method is essentially the same as that found in AutoCAD Release 14 and earlier versions.
Named plot style method. Assign named plot styles to layers and/or objects, and then use a named plot style table (STB file) to map the named plot styles to plotted lineweights. This method wasn't possible before AutoCAD 2000 because earlier versions didn't have plot styles.
Object lineweight method. Assign lineweights directly to layers and/or objects, and then plot the lineweights. This method wasn't possible before AutoCAD 2000, either, because earlier versions didn't offer lineweight as a layer and object property.
At first glance, the object lineweight method may seem like the most sensible approach. It's simple and direct and avoids the complication of an extra plot style table file. In fact, this method turns out to be too simple for almost everyone. Although it handles plotted lineweights, it doesn't address screening (a common technique for making some lines appear faded or grayed out) and other plotting effects that you can control with plot styles. So you'll probably need that plot style table file anyway.
In addition, it's hard to judge each object's lineweight on the screen. You can turn on lineweight display and fiddle with the display settings, but a computer screen just doesn't have the resolution to display small lineweight differences that are evident on plots. In other words, object lineweights aren't quite as WYSIWYG (What You See Is What You Get) as they seem at first.
Finally, and most importantly, object lineweights limit your plotting flexibility. If you always plot your drawings the same way, on the same size paper, with the same range of lineweights, then maybe you don't need plotting flexibility. But most people vary their lineweights to accommodate full-size vs. half-size plots, presentation vs. construction drawings, and other special output needs. Fixed object lineweights make these kinds of changes awkward, but plot styles make them relatively easy.
So if you want plotting flexibility, you're going to be using plot styles. But which kind: color-dependent or named?
There's no obvious logical reason to map screen color to plotted lineweight-that's just the way AutoCAD did it from v1.0 through Release 14. AutoCAD 2000 and later versions support this approach with CTB (color table) files, in which you map the 255 AutoCAD screen colors to lineweights and other plotted effects. The color-to-lineweight approach seems natural to those of us who've used AutoCAD for a long time, and as long as you always make monochrome plots, it generally works fine. But if you take off your Release 14-colored glasses for a moment, you realize that this plotted lineweight method is anything but natural. AutoCAD neophytes find it puzzling, and even veterans can get confused when they start to work with a new color-to-lineweight convention. Seeing object colors does help you distinguish the eventual plotted lineweights (once you're familiar with a particular mapping convention), but if you use more than a few well-defined colors, it's easy to make mistakes.
Probably the biggest argument against mapping colors to lineweights is color plotting. It's possible to make screen color serve two masters-plotted lineweight and plotted line color-but it's confusing and logically screwy.
For all these reasons, named plot styles in STB (style table) files seem like the way to go. With this approach, you create as many or as few plot styles as you need, name them as you wish (for example, Thin, Medium, Thick, Light Screen, Heavy Screen), and assign them to layers or to objects, just as you do colors and linetypes. You gain all the plotting flexibility of plot styles without the awkwardness of commandeering screen color for a purpose that has nothing to do with color.
For those who do sophisticated color plotting, named plot styles offer one other advantage: They work with the new true-color options in AutoCAD 2004. Color-dependent plot styles are limited to the 255 colors of the traditional ACI (AutoCAD Color Index) palette. That's more than enough for production drafting, of course, but it limits people in the publishing world.
Don't rush to throw out your CTB files just yet, though. Named plot styles, like object lineweights, increase the difficulty of judging on the screen what each object's lineweight will be when you plot. You can turn on the Display Plot Styles setting in a paper space layout's page setup, but as with object lineweights, small lineweight differences are difficult to detect on screen. Even worse, you won't see any lineweight differences when you view the Model tab.
For many people, an even bigger argument against named plot styles is compatibility with the rest of the AutoCAD-using world. Most of the companies with whom you exchange DWG files, including your plotting service bureau, likely use CTB files (or AutoCAD Release 14!). It's possible to create drawings that plot properly CTB-style and STB-style, but straddling this divide increases the probability of drawing exchange hassles immensely.
Of course, if everyone falls back on this justification, we'll never change anything. Sometimes you need to strike out on your own and hope that the laggards follow. Nonetheless, it's only prudent to make sure that your forward thinking doesn't leave you isolated from the other people and companies you work with.
FROM THE FIELD
I raised the question of which plotting approaches people use and why in the CAD Managers' discussion group-a pretty forward-thinking group on all AutoCAD-related matters.
Most respondents said that their companies continue to use color-dependent plot styles. The justifications range from inertia (users don't understand named plot styles, and companies don't want to pay for a change) to satisfaction with CTB files ("if it ain't broke, don't fix it") to compatibility with other companies. A couple of people mentioned that some AutoCAD applications don't fully support STB.
Several CAD managers emphasized how colors, unlike object lineweights and named plot styles, are easily "readable" on screen. Say what you will about the peculiarity of mapping color to lineweight, once someone understands that, for example, red means thin, cyan means medium, and magenta means thick, that person can easily check lineweights just by looking at the screen. A couple of CAD managers, however, led their companies in switching to named plot styles and were quite happy with the change. These companies typically did more color plotting or had a higher percentage of newer AutoCAD users, who aren't as wedded to the color-to-lineweight approach.
PICK YOUR PLOT STYLE
The lesson here is that plot styles are here to stay, and that both the CTB and STB approaches are viable. Take a look at the kinds of plotting you do, the kinds of people who use AutoCAD in your company, and the compatibility issues with other companies, applications, and older drawings.
I'm sure that all of us-software developers and users alike-will continue to craft better ways of creating, storing, and using digital data. In the meantime, let's not lose sight of what good paper drawings look like.
About the Author: Mark Middlebrook
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