Chapter 2 Creating Primitives and Composites 31 Copyright Goodheart-Willcox Co., Inc. If drawing the base from the center point, the polygon is circumscribed about the base circle by default. To inscribe the polygon on the base circle, enter the Inscribed option before setting the radius. To change back to a circumscribed polygon, select the Circumscribed option before setting the radius. After locating and sizing the base, you are prompted for the height. To create a frustum pyramid, enter the Top radius option. Then, set the radius of the top circle. The top will be either inscribed or circumscribed based on the base circle. You are then returned to the height prompt. The height value can be set by entering a direct distance. You can also use the 2Point option to set the height. With this option, pick two points on screen. The distance between the two points is the height value. The Axis endpoint option can also be used to specify the center of the top in the same manner as for a cone or cylinder. PROFESSIONAL TIP PROFESSIONAL TIP Six-sided frustum pyramids can be used for bolt heads and as “blanks” for creating nuts. Sphere A sphere is a round, smooth object like a baseball or globe. Once the command is initiated, you are prompted for the center of the sphere or to enter an option. If you pick the center, you must then set the radius of the sphere. To specify a diameter, enter the Diameter option after specifying the center. The 3P, 2P, and Ttr options are used to defi ne the sphere using three points on the surface of the sphere, two points on the surface of the sphere, or two points of tangency on the surface of the sphere and a radius. Spheres and other curved objects can be displayed in a number of different ways. The manner in which you choose to display these objects should be governed by the display requirements of your work. Notice in Figure 2-13 the lines that defi ne the shape of the spheres in a wireframe display. These lines are called contour lines, also known as tessellation lines or isolines. The Visual Styles Manager can be used to set the SPHERE Ribbon Home Modeling Solid Primitive Sphere Type SPHERE Figure 2-12. A sampling of pyramids that can be constructed with the PYRAMID command.