Getting the 3D Results You Want


You've seen how to make an opaque vertical surface just by changing the thickness property of an object. To make a horizontal surface appear opaque, you can draw it with a wide polyline, a solid hatch, or a 3D Face. For example, consider a table. You might represent the tabletop with a rectangle and give it the appropriate thickness , but the top appears to be transparent when the lines are hidden. Only the sides of the tabletop become opaque. To make the entire tabletop opaque if the tabletop is an irregular shape, you can use a solid hatch or an object called a region. Chapter 18 discusses regions . When the lines are hidden, the tabletop appears to be opaque (see Figure 15.17).

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Figure 15.17: One table using lines for the top, and another using a solid fill

When a circle is used as an extruded form, the top surface appears opaque when you use the Hide command. If you want to show an opening at the top of a circular volume, as in a circular chimney, you can use two 180 ° arcs (see Figure 15.18).

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Figure 15.18: A circle (left) and two joined arcs (right)
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Setting Layers and Hidden Lines Carefully

Bear in mind that the Hide command that you used first to hide the Wireframe view hides objects that are obscured by other objects on layers that are turned off. For example, if a couch in the corner of the studio unit is on a layer that is off when you use Hide, the lines behind the couch are hidden even though the couch does not appear in the view, as shown here.

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You can, however, freeze any layer containing objects that you do not want affected by the hidden-line removal process. This is important to be aware of because the Hide command reproduces what you see when you plot your drawing. In fact, you can use the Hide command to test your 3D model before you print.

You might notice that AutoCAD does not always display the intersection of 3D surfaces properly. You can set up AutoCAD to always display surface intersections by turning on the Display intersections option in the Hidden Line Settings dialog box. To open the Hidden Lines Settings dialog box, enter Hlsettings at the command prompt. You can also enter Intersectiondisplay 1 to turn on this feature.

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For complex horizontal surfaces, you can use a combination of wide polylines, solids, and 3D Faces. For example, a sidewalk on a street corner would use a donut for the rounded corner and would use solids or 3D Faces at either side for the straight portion of the sidewalk. It's okay to overlap surfaces to achieve the effect you want. Polylines are useful for creating window mullions or other shapes that might be formed by a straight extrusion in the real world. (You'll learn how to create a curved extruded shape in Chapter 18.)




Mastering AutoCAD 2005 and AutoCAD LT 2005
Mastering AutoCAD 2005 and AutoCAD LT 2005
ISBN: 0782143407
EAN: 2147483647
Year: 2004
Pages: 261
Authors: George Omura

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