Part IV introduces you to three-dimensional drawing. AutoCAD creates three types of 3D objects (also called models): wireframes, surfaces, and solids. Wireframes, as the name implies, look like models created with wire. They don't have real surfaces or solidity. However, they're useful for creating shapes that you can turn into surfaces or solids. Surfaces, unlike wireframes, can hide objects behind them. They're especially useful for creating unusually shaped objects. Solids are defined as the entire volume of space that they enclose. You can add and subtract solids from each other, creating realistic objects.

AutoCAD LT can create only wireframes and 2D objects with thickness, which is a kind of surface. Although AutoCAD LT's 3D capabilities are quite limited, you can still create simple 3D objects. Furthermore, AutoCAD LT can open and display a drawing that contains 3D objects created in AutoCAD.

In Chapter 21, I explain the basics of 3D drawing. This includes specifying 3D coordinates, using the User Coordinate System for 3D drawing, and creating objects with elevation and thickness. Chapter 22 explains the techniques for viewing, and navigating through, 3D objects. Chapter 23 covers surface models. Chapter 24 explains how to create true solids, and covers editing in three dimensions. Chapter 25 explains how to create photorealistic views of your 3D drawings using the AutoCAD rendering feature.

Chapters 23 through 25 apply only to AutoCAD.