21 Copyright Goodheart-Willcox Co., Inc. Learning Objectives After completing this chapter, you will be able to: ✓ Construct 3D solid primitives. ✓ Explain the dynamic feedback presented when constructing solid primitives. ✓ Create complex solids using the UNION command. ✓ Remove portions of a solid using the SUBTRACT command. ✓ Create a new solid from the common volume between two solids. ✓ Create regions. Overview of Solid Modeling Overview of Solid Modeling In Chapter 1, you were introduced to the three basic types of 3D models—wire- frame objects, solid models, and surface models. A solid model is probably the most useful and, hence, most common type of 3D model. A solid model accurately and realistically represents the shape and form of a fi nal object. In addition, a solid model contains data related to the object’s volume, mass, and centroid. Solid modeling is very fl exible. A model can start with solid primitives, such as a box, cone, or cylinder, and a variety of editing functions can then be performed. Think of creating a solid model as working with modeling clay. Starting with a basic block of clay, you can add more clay, remove clay, cut holes, round edges, etc., until you have arrived at the fi nal shape and form of the object. PROFESSIONAL TIP PROFESSIONAL TIP Snaps can be used on solid objects. For example, using 2D object snaps, you can snap to the center of a solid sphere using the Center object snap. The Endpoint object snap can be used to select the corners of a box, apex of a cone, corners of a wedge, etc. Using 3D object snaps, you can snap to the vertex or midpoint of an edge or to the center of a face. Creating Primitives and Composites CHAPTER 2 2