LESSON 3-3 - WORKING IN 3 DIMENSIONS

THE 3-D CO-ORDINATE SYSTEM

By now you should be very comfortable working your way around the X-Y co-ordinate system. Anyway, here is a quick review. Looking from the plan (top) view, this is what you see to figure out where is positive X and positive Y.

If you were to look at the same picture, but at a slight angle, you would see the third axis. This new axis is called the Z-axis. Imagine that the positive Z-axis is coming towards you out of the monitor.

The Z-axis has always been there, lurking in the background, waiting for you.

When you entered points previously, you would enter them in the format: X,Y. By doing this, you let AutoCAD know that in these cases, Z was equal to zero. Entering 4,3 would be the same as entering 4,3,0. Now if you drew a line from the origin (0,0,0) to a point at 4,3,2, you would get a line that goes 4 inches to the right, 3 inches up and 2 inches towards you. The properties of this line would be this:

Notice that the line is actually 5.3852" long. If you were to look at it from the plan view, it would look exactly like a line drawn from 0,1 to 4,4 Draw it and then check the properties. The difference is that a line to 4,4,0 would only be 5" long.

Why is this important to look at before entering the world of 3-D? If you were to only look at a 3-D model from the plan (top) view, you would not be able to see any difference between the two lines. (Draw them and see for yourself) On a 3-D model, you can easily have many points over top of each other. This would be very difficult to work with. You may think you're snapping to a particular endpoint, but the reality of it could be very different (think of how the top of the wall looks the same as the bottom of the wall if you're looking straight down it). Fortunately, AutoCAD provides different viewing options for 3-D drafting. This will be discussed in a later lesson, but for now, if you want to see your 2 lines in a view similar the Z-Axis image above, go to your menu called View > 3D Views > SW Isometric. You'll see the lines that look identical in the top view, look very different when viewed from an angle.

Now for the confusing part. You also have to know how AutoCAD measures angles of rotation in 3-D. There is a somewhat simple rule for this called "The Right Hand Rule". To figure out which is the positive rotation angle, imagine that you are wrapping your right hand around the axis with your thumb pointing towards the positive end. The direction that your fingers are wrapped is the positive direction. This applies to all three axes.

DIRECTION OF POSITIVE ROTATION

The main point of this lesson is to tell you that objects can trick you in 3D space. Shortcuts don't always work, you have to be careful with Osnaps and your drawing can turn into a mess very quickly if you're not paying attention. Trust me, I've seen enough students take the easy route and have to start over.