Copyright Goodheart-Willcox Co., Inc. Chapter 10 Advanced Surface Modeling 241 Removing Surface Associativity The surface associativity can be removed from a surface once the surface has been created. This can be done by selecting the surface and opening the Properties palette. The Maintain Associativity property in the Surface Associativity category controls the associativity of the surface. See Figure 10-4. By default, the property is set to Yes. Selecting Remove from the drop-down list removes the associativity and changes the property to None. This converts the surface to a generic surface. The Show Associativity property in the Surface Associativity category controls whether adjoining associative surfaces are highlighted when a surface is selected in order to indicate dependency. When this property is set to Yes and a surface is selected, AutoCAD highlights other surfaces to which the surface is dependent. This can be useful for identifying associative relationships in a chain of surfaces. PROFESSIONAL TIP PROFESSIONAL TIP When moving, scaling, or rotating an associative surface, be sure to select the under- lying curve geometry defi ning the surface. Failure to select the underlying geometry will result in the loss of the associativity. Determining Modeling Workfl ows for Procedural Surfaces and NURBS Surfaces When the design of a 3D model requires a freeform shape that would be diffi cult to create using solids, start by creating a procedural surface. You can convert the surface as required. A practical application is creating a surface model of a car fender. Start with a lofted surface based on four guide curves. Finish creating the fender by creating several procedural surfaces or patches, as discussed later in this chapter. Then, convert the fender surfaces to NURBS surfaces as needed and add further editing techniques for a more freeform sculpted shape. Different factors determine when to use procedural surface modeling and NURBS surface modeling. For example, create procedural surfaces when it is important to maintain associativity and you plan to edit the original geometry. On the other hand, NURBS surfaces have control vertices that typically permit greater fl exibility when editing. NURBS surfaces are often very useful for modeling organic shapes. The extent to which the design will require further editing can serve as a guideline for deter- mining the best modeling approach. The following sections discuss surface modeling commands and techniques avail- able in AutoCAD. Procedural surfaces are shown in examples as the default creation method. NURBS surface creation and editing techniques are covered later in this chapter. Figure 10-4. Associativity settings for a surface are accessed in the Properties palette. Select Remove from the drop-down list to remove associativity