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Figure 22-16: This cursor location results in the viewpoint shown in Figure 22-17.

Figure 22-17: This viewpoint results from the cursor location on the compass shown in Figure 22-16.

Getting a Quick Plan View

The PLAN command is a quick way to return to plan view. Type plan . This command has three options:

<Current UCS>: This is the default. You get the plan view of the current UCS.

UCS: The UCS option enables you to choose a named UCS. Type ? to get a list of the named UCSs. Otherwise, type the name of a UCS.

World: This option gives you the plan view of the WCS. If your current UCS is the WCS, there is no difference between this option and the Current UCS option.

Figure 22-18 shows a sample UCS listing. Note that the units are architectural.

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Returning to plan view when you change the UCS

If you like plan views, you’ll love UCSFOLLOW. UCSFOLLOW is a system variable that returns you to plan view whenever you change the UCS. It’s for those who like to get their bearings in plan view first before going on to change the viewpoint in another UCS.

Most 2D objects you use in 3D drawings can only be drawn and edited in plan view because they don’t interpret the Z coordinate. Therefore, returning to plan view is helpful in many situations.

The default value is 0 (off), which means that your drawing does not return to plan view. In other words, your display remains unchanged when you change the UCS. Type ucsfollow and change the value to 1 to turn UCSFOLLOW on. From then on, your drawing automatically displays the plan view when you change the UCS.

Figure 22-18: A listing of saved UCSs.

The Express Tools’ extended PLAN command, EXPLAN, prompts you to select objects so that you can see the plan view zoomed in on those objects. Choose Express Tools Extended Plan. For information about installing Express Tools, see Appendix A.

Shading Your Drawing

Shading is a simple version of rendering. You can use shading to get a quick visualization of your drawing. Shading is based on one default light source that is behind the viewer and shines on the model.

Shading is different in AutoCAD and AutoCAD LT, as follows:

In AutoCAD, you can edit your objects in Shaded mode. When you select shaded objects, the wireframe display and grips appear over the shading to help you work. Objects remain shaded until you choose to unshade them, even if you regenerate or close and reopen the drawing. You can display different shading in different viewports. Because shading can now stay on as you edit, it has been transformed from a simple form of rendering into a means of viewing your drawing while you work.

In AutoCAD LT, you cannot edit your objects in Shaded mode, which is a better-looking version of the HIDE command. If you regenerate the drawing, the shading goes away.

Objects in color shade better than objects in black and white.

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Using the shading options in AutoCAD

To shade in AutoCAD, choose View Shade or type shademode . Here are the options:

2D Wireframe: Displays objects in the familiar wireframe display, with no shading. Choose this option to return to “normal.”

3D Wireframe: Displays objects in wireframe along with a shaded UCS icon. Raster (bitmap) and OLE (embedded) objects, linetypes, and lineweights are not visible.

Hidden: Equivalent to using the HIDE command.

Flat Shaded: Creates flat blocks of color between each polygon face. There is no smoothing from face to face.

Gouraud Shaded: Creates smoothed shading from face to face, resulting in a more realistic appearance, especially for curved surfaces.

Flat Shaded, Edges On: Combines flat shading and wireframe display. Useful for editing objects while they’re shaded.

Gouraud Shaded, Edges On: Combines Gouraud shading and wireframe display. Useful for editing objects while they’re shaded.

Note The FACETRATIO system variable affects the mesh density created for cylindrical and conic solids. By default, it is set to 0 (zero), which creates the normal mesh density. Set it to 1 to increase the mesh density. This should improve the quality of rendered and shaded cylindrical and conic solids.

Using the shading options in AutoCAD LT

The SHADEMODE command in AutoCAD LT has only two options — 2D Wireframe and Hidden. The 2D Wireframe option allows you to turn off the shading in a viewport set for one of the options only available in AutoCAD. However, AutoCAD LT has a SHADE command that provides the following options:

256 Color: Displays shaded faces. Shading is flat, but curved faces give the impression of gradual shading because they’re broken up into many faces, each a slightly different color.

256 Color Edge Highlight: Like 256 Color, but highlights edges using the same color as your drawing background.

16 Color Hidden Line: Looks like a hidden display. The non-hidden edges are in the object’s color and the faces are the color of the background of the drawing area.

16 Color Filled: The reverse of 16 Color Hidden Line, so that the faces are in the object’s color and non-hidden edges are the background color.

Using materials

Materials are used in rendering, which is covered in Chapter 25. You can set your 3D graphics system display properties to display materials that you’ve attached to objects. Then, shaded objects display these materials. You can also display lights and textures. The difference in the quality of your image is striking. You can see the effect in 3D orbit as well when you use one of the shading options.

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New	You can now display backgrounds that you create with the BACKGROUND command. See
Feature	Chapter 25 for more information on backgrounds.

Lights in 3D orbit and SHADEMODE do not display shadows, have no attenuation, and use a default light intensity instead of the light intensity specified with the LIGHT command. Materials in 3D orbit and SHADEMODE display the color/pattern material component only. 3D textures are not shown; neither are bump maps, opacity maps, refraction, and reflection. For more information, see Chapter 25.

Here’s how to set your display to show materials, textures, lights, and a background:

1.Choose Tools Options and choose the System tab.

2.In Current 3D Graphics Display, choose your graphics system (it’s probably already selected) and click Properties.

3.In the 3D Graphics System Configuration dialog box, check Render Options.

4.Check the types of effects you want to display. You can choose to display a background, lights, materials, and textures.

5.Choose one of the transparency options: high, medium, or low quality.

6.Click Apply & Close.

7.Click OK to close the Options dialog box.

For information about how to attach a material to an object, see Chapter 25. Figure 22-19 shows a model with the Brassy Valley material attached, viewed with Gouraud shading.

Figure 22-19: A model with Gouraud shading and the

Brassy Valley material attached. (It looks better in color!).

On the	The drawing used in the following Step-by-Step exercise on shading a drawing, ab22-b.
CD-ROM	dwg, is in the Drawings folder on the CD-ROM.

This exercise is for AutoCAD only. AutoCAD LT doesn’t offer these shading options.