Specifying Exact Distances in 3D Space

When you draw in 2D, the z-axis is fairly unimportant. By default, objects you create reside at the 0 (zero) coordinate of the z-axis. In other words, everything you draw is on the plane defined by the x-and y-axes. But just as you can move and copy objects anywhere in the XY coordinate plane, you can also move and copy them along the z-axis.

Just as you can specify exact distances in 2D drawings, you can specify locations and distances in 3D space using the @X,Y,Z notation. If you want to move something only within the XY plane, you can omit the Z coordinate in the specification, and AutoCAD assumes you want to maintain the object's current Z coordinate. To specify relative distances in 3D, you can specify the Z coordinate as needed, as shown here:

 @2,1,1↲ 

If you enter this at the Specify second point or [Exit/Undo] <Exit>: prompt in the Move or Copy command, your object not only moves 2 units to the right and 1 unit up, but it also moves 1 unit vertically, in the positive direction of the z-axis (see Figure 6.39).

Figure 6.39: The image on the top shows an object moved within the XY plane within the WCS. The image on the bottom shows the same move with an additional Z component.

If you want to move an object only in the z-axis, enter 0 for both the x-and y-axes, as in @0,0,2↲. This moves your selected object 2 units in the positive direction of the z-axis.

You might find it easiest to remember the @X,Y,Z format for specifying distances in 3D, but in typical AutoCAD fashion, you can use two other formats for spatial distances. In the limited space of this book, however, I can't show all the methods for specifying distance in 3D. For future reference, the other methods are the cylindrical format and the spherical format. Both are extensions of the standard AutoCAD polar coordinate format you use in 2D drawing. You can find out more about these formats in Mastering AutoCAD 2008 and AutoCAD LT 2008, published by Sybex.