rotating an area about a line (axis of rotation). Examples of these volume-generating operations
are shown in Figure 16.23.
With top-down modeling, you can create surfaces or three-dimensional solid objects using
area and volumeprimitives. Primitives are simple geometric shapes. Two-dimensional primitives
include rectangles, circles, and polygons, and three-dimensional volume primitives include
blocks, prisms, cylinders, cones, and spheres, as shown in Figure 16.24.
Regardless of how you generate areas or volumes, you can use Boolean operations to add
(union) or subtract entities to create a solid model. Examples of Boolean operations are shown
in Figure 16.25.524 Chapter 16 Engineering Drawings and Symbols
■Figure 16.21
Examples of computer-generated
solid models.62080_16_ch16_p504-549.qxd 5/22/10 12:31 AM Page 524
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