First Draft, Then Edit (Pt. 2)

Here's part two of the Young Lady's CAD Primer. I'm sorry if these posts are a bit dry, but I thought it might be worthwhile. Tomorrow's post should have some more pics, and then on Monday I'll show you the progress I've made on my office building, which is just about finished. If you have a suggestion for the sort of building I should do next, feel free to stand up and be counted in the comments section.

CAD is all about marking points with your cursor, usually to make some kind of line connecting them. There are a lot of time-saving shortcuts to let you draw rectangles, octagons, circles and arcs with just a few button clicks, but these functions can all be accomplished by making a lot of lines connecting a lot of little points if you really wanted to.

And the great thing about making lines and points in AutoCAD is that you can specify exactly where the points should be, to whatever precision you want. The reason you can do this is because the infinitely big area you work in is divided into a big Cartesian plane. (The Cartesian plane is named after a really incredible guy named Renee Descartes who was a mercenary, philosopher (ever heard of "I think, therefore I am"? That's his), and mathematician. It's basically just two arrows crossed at right angles that allow you to assign an exact value to every inch of space in a two-dimensional plane. And as I remarked the other day, it's easy to extrapolate that into a third dimension to name every point in a 3D space.) This means that you can draw a huge office building plan, then zoom in and draw the bathroom fixtures exactly where they should go.

And while all this is great, the real trick about CAD software is that it allows you to draw things in the same drawing on different layers, allowing you to separate some elements to make your drawings more clear. The best way to visualize this is to think of an anatomy book that shows the human body with all it's skin and muscle and bone and nerves, except that each type of tissue is on a different piece of clear acetate stacked neatly over the silhouette on the backing page. That way, you can pull back each layer and get a look at how everything fits into a human body, without having to have half a dozen separate drawings. For example, an architect might draw a house on the computer that has all of the plumbing on one layer, the electrical wiring on another, the heating/AC ducts on another, and the furniture on another. That way, he can show the where the plumber what he's supposed to do without confusing him with what the electrician is supposed to do, all with just a couple of button clicks. It's especially handy for showing things like a reflected ceiling plan, in which you show where all the ceiling tiles will go and how the lights are arranged. If you have this info turned on on the same time as the floor tile plan, things can get awfully crowded very quickly.

The funny thing is that the layers are the thing that makes computer drafting so amazing, yet it actually grew out of an old-school practice of making plans just like the anatomical drawing I talked about. You would have some pegs at the top of your drafting table that would hold several sheets of tracing paper, and you would just copy your main drawing over and over onto each layer to do your electrical, plumbing, etc plans.

Tomorrow I'll show some images of what a skilled draftsperson can create on CAD software and talk a little about the future of drafting, then I promise I'll get back to something a little more interesting.