242 AutoCAD and Its Applications—Advanced 242 AutoCAD and Its Applications—Advanced Creating Network Surfaces Creating Network Surfaces A network surface is a surface model created by a group or “network” of profi le curves or edges. A network surface is similar to a loft surface. As with a loft, the defi ning profi les can be open or closed curves, such as splines. The defi ning profi les can also be the edges of existing objects, including region edges, surface edge subobjects, and solid edge subobjects. The curves or edges selected can intersect at coincident points, but do not have to intersect. The SURFNETWORK command is used to create network surfaces. After selecting this command, select the curves or edges defi ning the fi rst direction of the surface. Make sure to select the curves in the order of surface creation. Then, press [Enter]. Next, select the curves or edges defi ning the second direction of the surface. Press [Enter] when you are done selecting the profi les. This creates the surface and ends the command. See Figure 10-5. A network surface is created as an associative surface by default. The curves selected for the two directions defi ne the U and V directions of the surface. The U and V directions can be thought of as the local directions of the surface and can be defi ned in either order. The U and V directions defi ne the “fl ow” of the surface. Figure 10-6 shows examples of creating network surfaces from similar sets of profi le curves. In Figure 10-6A, a series of connected profi le curves defi nes the network surface. In Figure 10-6B, two of the curves do not intersect with other profi les. Notice the differences between the resulting surface models. Creating a network surface from region edges, surface subobject edges, and solid subobject edges is shown in Figure 10-7. Creating a network surface in this manner may result in some unexpected surface shapes. To select the profi le edges, press and hold the [Ctrl] key. You can also use the edge subobject fi lter by selecting Edge from the Selection panel in the Home tab of the ribbon. In Figure 10-7, the four objects are located at different “Z” heights. The network surface is created from the four nonin- tersecting edges. Referring to Figure 10-6, when working in a wireframe display, isolines appear to represent the curved surfaces of the surface model. The SURFU and SURFV system variables control the number of isolines displayed in the U and V directions of the surface. The number of isolines does not include the lines defi ning the object’s SURFNETWORK Ribbon Surface Create Network Surface Type SURFNETWORK A B 3 2 1 4 5 6 7 8 Figure 10-5. Creating a network surface. Splines are used as the profiles in this example. A—The profiles used to define the surface are selected in the numbered order shown. Profiles 1–3 define the first direction and are shown in color. Profiles 4–8 define the second direction. B—The resulting surface model.