AutoCAD® 2012 FOR DUMMIES®

Modeling from Above

So far in this book, you've been working with X- and Y-coordinates only. X- and Y-coordinates by themselves define a two-dimensional plane known (logically enough) as the X,Y plane.

In this and the following two chapters, you supply a third value, a Z-coordinate, in order to locate geometry above or below the X,Y plane. You use the same methods to specify Cartesian (X,Y,Z) coordinates as the ones I set out in Chapter 7 — you just add a comma and another number. The following techniques can be used to specify points in 3D:

• Coordinate and direct distance entry
• Point filters
• Object snaps
• 3D object snaps
• Object-snap tracking

Using 3D coordinate input

I introduce you to 2D coordinate entry in Chapter 7. To recap, the input formats are:

• Absolute Cartesian coordinates: Expressed as X,Y — the distances along the X- and Y-axes from the origin (0,0).
• Relative Cartesian coordinates: Expressed as @X,Y — the distances parallel to the X- and Y-axes from last point.
• Relative polar coordinates: Expressed as @d<a — the distance and angle in the X,Y plane from the last point.

While you can use these 2D coordinate input methods in 3D, you usually have to give AutoCAD just a little more information when you want to work in three dimensions. You can use absolute or relative Cartesian coordinates by simply adding a Z-coordinate to the end. In addition, there are two 3D-only coordinate formats, both based on 2D polar coordinates. You can enter 3D coordinates using the following ...