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AutoCAD 2016 Introducing 3D Concepts by David Cohn AutoCAD provides many powerful tools for working in 3D. The program supports four different types of three-dimensional models: Wireframe models consist of lines and curves that defi ne the edges of a 3D object. You can create a wireframe model by drawing lines, arcs, polylines, and other 2D objects anywhere in 3D space. Wireframe models have no surfaces; they always appear as outlines. Because you must individually draw and position each object that makes up a wireframe model, creating them can be exacting and time-consuming. Surface models represent an infi nitely thin shell that corresponds to the shape of a 3D object. Surface models consist of both edges and the surfaces between those edges. You can create surface models by using specifi c surface modeling commands or by sweeping, lofting, and revolving two-dimensional objects such as lines and arcs. Solid models consist of both the surfaces and the volume inside those surfaces. A solid model is a 3D representation that has such properties as mass, volume, center of gravity, and moments of inertia. You create solid models either by Watch Video here using specifi c solid modeling commands to create basic shapes such as boxes, cones, cylinders, spheres, and so on, or by sweeping, lofting, or extruding closed 2D objects. You can also combine solids using Boolean operations such as subtract, union, and intersect to create more complex solids. Solids are easier to construct than surface or wireframe models. However, if needed, you can break solids down to surface and wireframe objects. A mesh consists of vertices, edges, and faces that use polygonal representations such as triangles and quads to defi ne a 3D shape. Unlike solid models, meshes have no mass properties. But mesh objects offer unique capabilities not available for 3D solids or surfaces. For example, you can apply creases, splits, and increasing www.cadlearning.com 13 1313