Copyright Goodheart-Willcox Co., Inc. Chapter 10 Advanced Surface Modeling 239 surface. Referring to Figure 10-1, notice the Surface Associativity and NURBS Creation buttons in the Create panel. The status of the Surface Associativity button indicates the SURFACEASSOCIATIVITY system variable setting. By default, the button has a blue background to indicate the system variable is turned on. The status of the NURBS Creation button indicates the SURFACEMODELINGMODE system variable setting. By default, this button does not have a blue background. This indicates that procedural surfaces are created by default. PROFESSIONAL TIP PROFESSIONAL TIP Procedural surfaces are also referred to as explicit surfaces. The terms procedural surface and explicit surface are interchangeable. This text uses procedural surfaces to illustrate various methods of surface creation. NURBS surfaces, as discussed later in this chapter, are used in creating models that represent sophisticated freeform shapes. Procedural surfaces can be converted to NURBS surfaces in order to model more sophisticated surface model shapes. NOTE NOTE Planar surface creation is discussed in Chapter 2. Extruded and revolved surfaces are discussed in Chapter 6. Swept and lofted surfaces are discussed in Chapter 7. Exercise 10-1 www.g-wlearning.com/CAD/ Complete the exercise on the companion website. Working with Associative Surfaces Procedural surfaces, when created, are associative by default. An associative surface adjusts to the modifi cations made to the defi ning profi le geometry (or other adjoining surfaces). This provides fl exibility in the design. However, it is important to remember that when modifying the shape of an associative surface, you modify the profi le geometry, not the surface. Modifying the profi le geometry maintains the asso- ciative relationship. If you pick on the surface and then attempt to modify it, AutoCAD issues a warning that the surface will lose its associativity with the defi ning curve, surface, or parametric equation. If you choose to continue with the operation, the asso- ciativity is lost. You can cancel the operation to preserve the associativity. Figure 10-1. The Surface tab of the ribbon. Picking this button sets the value of the SURFACEASSOCIATIVITY system variable Picking this button sets the value of the SURFACEMODELINGMODE system variable