Chapter 2 Creating Primitives and Composites 33 Copyright Goodheart-Willcox Co., Inc. to 2047. Figure 2-13B displays spheres with 20 contour lines. It is best to use a lower number during construction and preliminary displays of the model and, if needed, higher settings for more realistic visualization. The contour lines setting is also avail- able in the Display tab of the Options dialog box or by typing ISOLINES. The Draw true silhouettes setting in the 2D Wireframe options area of the Visual Styles Manager controls the display of silhouettes on 3D solid curved surfaces. The setting is either Yes or No. Notice the sphere silhouette in Figures 2-13C and 2-13D. The Draw true silhouettes setting is stored in the DISPSILH system variable. Torus A basic torus is a cylinder bent into a circle, similar to a doughnut or inner tube. There are three types of tori. See Figure 2-15. A torus with a tube diameter that touches itself is called self intersecting and has no center hole. To create a self-intersecting torus, the tube radius must be greater than the torus radius. The third type of torus looks like a football. It is drawn by entering a negative torus radius and a positive tube radius of greater absolute value, such as –1 and 1.1. Once the command is initiated, you are prompted for the center of the torus or to enter an option. If you pick the center, you must then set the radius of the torus. To specify a diameter, select the Diameter option after specifying the center. This defi nes a base circle that is the centerline of the tube. The 3P, 2P, and Ttr options are used to defi ne the base circle of the torus using either three points, two points, or two points of tangency and a radius. Once the base circle of the torus is defi ned, you are prompted for the tube radius, or to enter an option. The tube radius defi nes the cross-sectional circle of the tube. To specify a diameter of the cross-sectional circle, enter the Diameter option. You can also use the 2Point option to pick two points on screen that defi ne the diameter of the cross- sectional circle. If you are working conceptually, you can move the pointer and see the tube size change dynamically. Wedge A wedge has fi ve sides, four of which are at right angles and the fi fth at an angle other than 90°. See Figure 2-16. Once the command is initiated, you are prompted to select the fi rst corner of the base or to enter an option. By default, a wedge is constructed by picking diagonal corners of the base and setting a height. To pick the center point, TORUS Ribbon Home Modeling Solid Primitive Torus Type TORUS TOR WEDGE Ribbon Home Modeling Solid Primitive Wedge Type WEDGE WE Figure 2-15. The three types of tori are shown as wireframes and with hidden lines removed.