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COPYRIGHT 2001 Questex Media Group, Inc.
Mention CAD standards and the first thing that springs to most people's minds is layer standards: how to name them, what properties to assign to them, and which objects belong on them. There is some truth to this association. Although CAD standards comprise a lot more than just layer standards, layers are a central part of how we create and plot drawings. In the AEC professions, layers take on additional significance. Because design and construction teams exchange many AEC drawings electronically, layer names and use reverberate beyond an individual office. They become project-wide and ultimately industry-wide issues.
CADALYST has published numerous articles on CAD standards in general and AEC layer standards in particular, including our April 2000 feature article, "Build Your CAD Standards" (www.cadalyst.com/features/standards/standards.html). See "AEC Layer Standards Resources" for additional articles on the subject. This month, we take a fresh look at AEC layer practices--where AEC CAD layers have been, where they are, and where they're going.
Why bother?
Before we examine the what and how, let's consider the why. In other words, why bother trying to standardize layer names and use at all? I can think of four primary reasons:
Production efficiency. It's usually a lot faster to create drawings if everyone works with a prearranged, well-ordered set of layers--especially if you customize your CAD software to support and encourage the use of standard layers. On the other hand, overly complicated or badly implemented layer standards can slow down production.
Plotting consistency. Yes, most of us still plot a lot, and when we do, we want consistent output. Grid lines should be thin, text should be medium, and columns should be thick. All of the sheets for a project should be similarly formatted and read well. The key to this consistency is a reasonably standardized set of layers and layer properties, as well as a system whereby individual objects inherit their properties from the layers on which they reside. In AutoCAD terminology, this means color, linetype, lineweight, and plot style "by layer" rather than "by object."
Electronic consistency. The consistency of drawing data inside the CAD file is increasingly as important as the consistency of plotted output. In fact, electronic consistency can be more important if you use custom applications that manipulate or extract drawing data based on layers.
Ease of reuse by other people or companies (drawing exchange). In the AEC professions, design firms frequently make use of each other's drawings. For example, a plumbing drawing might use architectural or structural drawings as backgrounds. In many cases, one profession wants to show only some of the objects that appear on the other professions' full drawings. When layer use is inconsistent, this kind of partial reuse becomes extremely difficult.
Bernie Avery of ZTR Control Systems, a company specializing in industrial controller systems, provided this anecdote on the Autodesk-sponsored CAD Managers newsgroup:
"In a previous office, I had four operators producing up to 25 drawings each per day (a heavily customized system to produce drawings for manufacturing). Each operator maintained his or her own layer settings, although the names...
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