AutoCAD® 2012 FOR DUMMIES®

Understanding 3D Digital Models

There are three basic types of 3D computer model:

• Wireframe models: Consist of edges and vertices only. Although they do occupy 3D space, they're totally unrealistic and difficult to read correctly. AutoCAD doesn't create wireframe models, although you can view them as such.
• Surface models: Consist of infinitely thin skins that stretch from edge to edge of a model. AutoCAD can create two different types of surfaces: Mesh surfaces, composed of thousands and thousands of 3- or 4-sided faces, and NURBS surfaces (Non-Uniform Rational B-Splines, if you must know). Mesh surfaces tend to be a little imprecise; they're most often used for 3D animation or terrain modeling. NURBS surfaces are far more precise (as you'd expect with a name like that!) and are frequently used in product design. Due to space limitations, I don't cover either type of surface modeling in AutoCAD 2012 For Dummies.
• Solid models: Have edges, surfaces and mass. Solid models are the most complex type (although precise surface models can be more difficult to construct). Solid models can be assigned physical material properties such as steel or aluminum, and so mass, centers of rotation, etc can be calculated by the computer and displayed visually.

While surface and solid models are created and modified differently, the 3D objects that make up the models are made up of the same subobjects. The subobjects that a 3D object is made up of are

• Vertex: The 3D equivalent of an AutoCAD point ...