Chapter 24 Creating Solids and Editing in 3D

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Figure 24-45: The shelled box.

Listing Solid Properties

The MASSPROP command provides information about regions and solids that is useful for engineering applications. The bounding box, for example, is an imaginary box that contains the solid. The calculations are based on the relationship of the solid to the UCS. If you rotate the solid or change the UCS, you get different results. For example, after running MASSPROP to find the center of gravity (centroid) and axes of your model, move the UCS to the centroid and then run MASSPROP again to identify the moments of inertia.

For 2D regions, the area moment of inertia that MASSPROP generates can be used to calculate bending and twisting stresses. You could generate a 2D region of a solid model using the SECTION command and then use the UCS command with the OBJECT option to set the UCS coplanar to the region. The MASSPROP command would then report the area moment of inertia.

AutoCAD assumes a density of 1 for all solids. You can then apply material density multipliers on the values that get reported. Figure 24-46 shows the results of MASSPROP on a solid.

To list a solid’s properties, choose Tools Inquiry Region/Mass Properties. Select the object you want to list. AutoCAD opens the Text Window to display the calculations. At the Write analysis to a file? [Yes/No] <N>: prompt, press Enter to accept the No default, or right-click and choose Yes. AutoCAD prompts you for a filename and copies the data to that file.

744 Part IV Drawing in Three Dimensions

Figure 24-46: The results of the MASSPROP command.

Summary

In this chapter, you learned how to create and edit solids. You read about:

Drawing standard shapes

Creating extruded and revolved solids from 2D profiles

Using UNION, SUBTRACT, and INTERSECT to create more-complex shapes

Using the INTERFERE command to see the volume of interference between solids

Utilizing the SECTION and SLICE commands to help visualize solids

Using the special 3D editing commands MIRROR3D, 3DARRAY, and ROTATE3D

Using the TRIM, EXTEND, FILLET, and CHAMFER commands for 3D editing

Exploding into surfaces and surfaces into 2D objects

Using the SOLIDEDIT command to edit faces, edges, and bodies — solids as a whole

Calculating a number of engineering functions on solids by using the MASSPROP command

In the next chapter, I cover rendering 3D models.

Rendering in 3D

Although 3D drawings are more realistic than those rendered in 2D, they look very artificial — they lack realistic color, shading,

and lighting, for example. Rendering enables you to display a 3D drawing more realistically. Some of the more-advanced features let you create shadows, make objects transparent, add backgrounds, and map 2D images onto the surface of 3D models. You can shade and render 3D surfaces and solid models. Figure 25-1 shows a whimsical rendering that uses shadows and a background.

Figure 25-1: This cog has been rendered with shadows and a background of clouds.

AutoCAD LT does not offer any rendering feature. This entire chapter applies only to AutoCAD.

Understanding Rendering

Rendering is a much more sophisticated means of visualizing a drawing than shading. AutoCAD offers three kinds of rendering — Render, Photo Real, and Photo Raytrace.

Render is AutoCAD’s original rendering tool. It provides the fewest options but the fastest results.

Photo Real creates images line by line, displays bitmaps, creates transparent materials, and makes volumetric and mapped shadows.

Photo Raytrace traces rays of light to generate reflections, refraction, and precise ray-traced shadows.

25C H A P T E R

In This Chapter

Understanding rendering

Creating lights and scenes

Working with materials

Using backgrounds

Rendering your drawing

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Learning the steps

Rendering is a multi-step process. It generally requires a good deal of trial and error to get the exact results you want. Here are the steps to render a drawing:

1.Start with trial rendering using the default settings. The results let you know what settings need to be changed.

2.Create lights. AutoCAD has four types of lights: ambient, distant, point, and spotlight. I explain lights in the “Creating Lights” section later in this chapter.

3.Create scenes. Scenes are views with lights. See the “Creating Scenes” section later in this chapter.

4.Load materials from the materials library. You can create your own materials. Materials are surface characteristics and include color and/or pattern, ambient light, reflection, roughness, transparency, refraction, and bump map. These characteristics are explained later in this chapter in the “Working with Materials” section.

5.Attach materials to the objects in your drawing. You can attach materials by object, color, or layer.

6.Add a background or fog effect. See the “Using Backgrounds” section later in this chapter.

7.Set your rendering preferences, if desired.

8.Render the drawing.

The order of the steps is flexible. For example, you can create scenes after you’ve attached materials. Also, after you render, you’ll probably see some room for improvement, so you may go back and change the lights, scenes, and/or materials.

Doing a default rendering

Doing a default rendering often helps. The results help you decide what materials and lights you need to create and reveal any problems with the models themselves. When you render, you should open the Render toolbar, which contains most of the tools you need. Right-click any toolbar and choose Render.

To render a drawing using the default settings, choose Render from the Render toolbar to open the Render dialog box, shown in Figure 25-2.

I cover the Render dialog box later in the chapter, but there are a couple of things you can do when you’re trying to get a quick rendering.

You can save time by rendering only some of the objects in the view. To do this, use the Rendering Procedure section of the dialog box.

Check Query for Selections to tell AutoCAD to display the Select objects: prompt before rendering. AutoCAD renders only the objects you selected, instead of the entire drawing, saving time.

Check Crop Window to tell AutoCAD to prompt you to specify a window before rendering. By rendering only a section of the drawing, you can save time.

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In the Rendering Options section, check Render Cache if you plan to render the same scene several times, as is often the case when you’re working on a rendering. AutoCAD saves the rendering data in a file and uses it for subsequent renderings — saving the time needed for AutoCAD to analyze the drawing each time.

Click Render to render the drawing.

Figure 25-2: The Render dialog box.

On the	The drawing used in the following Step-by-Step exercise on creating a default rendering,
CD-ROM	ab25-a.dwg, is in the Drawings folder on the CD-ROM.

STEP-BY-STEP: Creating a Default Rendering

1.Open ab25-a.dwg from the CD-ROM.

2.Save the file as ab25-01.dwg in your AutoCAD Bible folder. If the Render toolbar is not displayed, right-click any toolbar and choose Render.

3.Choose Render from the Render toolbar. In the Rendering Procedures section

of the Render dialog box, check Crop Window. In the Rendering Options section, check Render Cache.

4. Click Render.

5. At the Pick crop window to render: prompt, pick a window similar to that shown in Figure 25-3. Wait until AutoCAD renders the drawing.

6.Save your drawing. It should look like Figure 25-3. As you can see, the rendering is too dark and the objects need realistic materials.