240 AutoCAD and Its Applications—Advanced 240 AutoCAD and Its Applications—Advanced Set the SURFACEASSOCIATIVITY system variable to 1 to create associative surfaces. If the system variable is set to 0, surfaces that are created have no associativity to defi ning profi le curves or other surfaces. An example of creating a procedural surface model is shown in Figure 10-2. In this example, an associative surface is created from a series of cross-sectional profi les using the LOFT command. As discussed in Chapter 7, a loft is created by selecting the cross-sectional profi les in order. In Figure 10-2A, four open profi le curves are selected to create the loft. By default, this creates a surface model. In Figure 10-2B, the object is shown after lofting. In Figure 10-2C, the object is shown after moving and scaling the third open profi le. Because the surface model is associative, the model updates and adjusts to conform to the new curve shape. In Figure 10-3, a loft surface is created from three closed cross-sectional profi les (circles). The surface is created by using the Mode option or by selecting the command from the Surface tab in the ribbon. In Figure 10-3B, the object is shown after moving and scaling the third closed profi le at the top. Because the surface is associative, the model updates and conforms to the new curve shape. PROFESSIONAL TIP PROFESSIONAL TIP The DELOBJ system variable is ignored if the SURFACEASSOCIATIVITY system vari- able is set to 1. Also, when creating a NURBS surface, the surface is a NURBS surface and is not associative. Profile to be edited A B C First profile selected Last profile selected Figure 10-2. Creating a loft surface as an associative surface model. A—The original cross-sectional profiles. B—The model after using the LOFT command. C—The model after editing one of the cross-sectional profiles. Figure 10-3. Modifying a loft surface created from closed profiles (circles). A—The original loft surface. B—The model after editing the closed profile at the top. A B Profile to be edited