AutoCAD 2005 for Dummies

Consider these issues before you decide how much to use 3D on a particular project:

? 2D input and editing: The mouse, keyboard, and drawing tablet are all 2D devices; the more complex the 3D object you’re trying to model, the more complicated it is to construct the object with these devices. In addition, the AutoCAD 3D editing tools are fairly limited in scope — especially for solids. For most heavy-duty 3D work, you need a third-party application, a discipline-specific version of AutoCAD (such as Architectural Desktop), or a special-purpose solid modeling program.

? 2D output: Most of the currently available output methods, notably paper and the computer screen, are 2D. Presenting your 3D model in its full, three-dimensional glory requires extra work by you or the viewer.

? Performance: Today’s personal computers are adequate for the task of storing fairly complex 2D models and displaying them on-screen and on plots; if the model is 3D, the difficulty increases geometrically, and performance seems to slow geometrically as well. You may need a faster computer and more memory to meet these demands. You may also find yourself taking longer coffee breaks as you wait for your computer to load or render complex 3D models.

Getting Your 3D Bearings

The first challenge in 3D modeling is being able to see your three-dimensional model on a two-dimensional computer screen. The normal model space view on the Model tab in the drawing area shows a single, projected 2D view of your model — the top-down, “plan” view by default.

AutoCAD provides two model space capabilities that enable you to escape this visual flatland:

? With viewports, you can carve the model space drawing area into smaller rectangular areas, each of which shows a different view of the model.

? With viewpoints, you can change the point in 3D space from which you look at the model. By setting a different viewpoint in each viewport, you can look at several sides of your model at the same time. It’s like looking at one of Picasso’s cubist paintings, only more orderly.

  If you want to experiment with viewports and viewpoints in an existing 3D drawing, try one of the AutoCAD2005 samples, such as Program FilesAutoCAD 2005SampleWelding Fixture Model.dwg. To remove shading and make the model faster to work with, choose View>Shade>2D Wireframe.

Model space viewports left and right

Chapter 3 discusses viewports in paper space, which are useful for creating layouts for use in plots and presentations in both 2D and 3D. Model space viewports, cousins of paper viewports, are less powerful but simpler and are intended to help you construct 3D models.

Model space viewports divide the screen into separate rectangles with no gaps between them. Unlike with paper space viewports, you can’t move, stretch, or overlap them. You can’t plot multiple model space viewports; that’s what paper space is for. And, unlike in layouts, a layer that’s visible in one model space viewport always is visible in all of them.

  You may hear or read references to tiled viewports, which is just another name for model space viewports. Tiled refers to the way in which model space viewports always fill the drawing area, with no gaps and no overlapping allowed. Conversely, paper space viewports are sometimes called floating viewports because you can move them around, leave gaps between them, and overlap them.

Model space viewports enable you to see several views of your model at one time, each from a different viewpoint. For this reason, model space viewports are especially useful when you’re creating and editing objects in 3D. As you draw and edit, the different views help ensure that you’re picking points that are located correctly in 3D space.

To set up model space viewports, use the Viewports dialog box:

1. Choose View>Viewports>New Viewports.

The Viewports dialog box appears.

2. Choose one of the Standard Viewport arrangements and choose 3D in the Setup drop-down list.

3. Click OK.

Figure 8-2 shows the dialog box and the model space result of choosing the Four Right Standard Viewport arrangement and the 3D Setup. This arrangement, along with the Four Equal, and Four Left standard viewport arrangements, works well for creating viewports that show top, front, right, and isometric views of a 3D model.

Figure 8-2: The Viewport dialog box makes setting up model space viewports and different viewpoints easy.

To return to a single viewport later, click in the one whose view you want to use, then open the Viewports dialog box and choose Single in the Standard Viewports list.

Seeing the world from new viewpoints

When you choose 3D in the Viewports dialog box’s Setup drop-down list, you direct AutoCAD to change the viewpoint in each viewport. The default viewpoints when you choose a four viewport arrangement are top, front, right, and isometric. These viewpoints work well for viewing and constructing simple models, but eventually, you’ll probably want to specify your own, custom viewpoint in a particular viewport.

The easiest way to change viewpoints is to use the View>3D Views submenu (shown in Figure 8-3) to switch to one of the standard orthographic 3D views or an isometric view:

? The six standard orthographic (straight-on) views are Top, Bottom, Left, Right, Front, Back.

? The four standard isometric views are SW (left-front), SE (right-front), NE (right-back), and NW (left- back). An isometric view is one in which you see the object from above, but not too high above — as though you were hovering in a low-flying helicopter.

These ten views are called standard because they’re often used in manual drafting and rendering work. They work well for showing 3D models of common objects such as mechanical components and buildings. (You can also change to plan view, which is a top-down view of either the world coordinate system or a user coordinate system. I describe coordinate systems in “A Cartesian Orientation,” later in this chapter.)

You can specify nonstandard viewpoints by choosing View>3D Views>Viewpoint Presets. In the Viewpoint Presets dialog box that appears, specify the following settings:

? A viewing angle in the XY plane (imagine moving a camera on a dolly around an object, while keeping the camera at the same elevation)

? An angle from the XY plane (imagine using a boom to swoop the camera up to a different height so that you’re looking at the object from increasingly steep angles)

Figure 8-3: The 3D Views submenu.

  By default, AutoCAD shows 3D models in 2D wireframe mode, even if you’ve created surface or solid objects. If you want to better visualize which objects are in front of which other objects, especially in an isometric or other nonorthogonal view, you have a couple of options:

? Choose View>Shade and then choose Hidden or any of the Shaded options.

? Render the model, as described later in this chapter.

Dynamic viewpoints with 3DOrbit

Standard views and the Viewpoint Presets dialog box are fine for many 3D construction tasks, but if you really want to have fun with a model, 3DOrbit is your ticket to it.