472 Part V: On a 3D Spree

This chapter takes a look at some of the tools available in AutoCAD 3D Modeling workspace and introduces you to many of the general concepts of creating 3D objects. You also discover how to look at your model from different viewpoints, and how to change the way it appears onscreen.

3D modeling and visualization is a lot more demanding on computer hardware than 2D drafting. 3D models tend to be bigger than 2D drawings, so you may need more disk space. And you’ll certainly be happier with more than the bare minimum of RAM required for 2D in AutoCAD. In Chapter 2, we list AutoCAD system requirements and point out the increased resources needed for 3D work. In particular, note the desirability of using an engineering graphics card as opposed to a gaming card for heavy-duty 3D work.

Understanding 3D Digital Models

Here are the three basic types of 3D computer models:

Wireframe models: Consist of edges and vertices only. Although they do occupy 3D space, they’re totally unrealistic and difficult to read correctly. AutoCAD can create wireframe models, but nobody does any more. You only need to view a complex 3D model in wireframe mode to understand why.

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 threeor foursided faces, and NURBS surfaces (Non-Uniform Rational Bezier Splines, if you must know). Mesh surfaces tend to be a little imprecise; they’re most often used for 3D animation or terrain modeling. Think of the mirror disco ball in a nightclub. From a distance, it looks like a sphere, but as you get closer, you can see that it is made up of many small flat patches. 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, we don’t cover either type of surface modeling in this book

Solid models: Have edges, surfaces, and mass. They are true 3D models, and so you can do interference checking between them to make sure that an assembly will fit together properly. You can also find the surface

area, volume, center of gravity, and moments of inertia of 3D models. Unfortunately, AutoCAD always assumes the material has a density of 1. If your real-life part is going to be made from something other than water, you will need to multiply the mass values by a suitable conversion factor, depending on the actual material being used.

AutoCAD has several commands related to applying materials to solids, but they affect only the appearance — not the density.

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