262 AutoCAD and Its Applications—Advanced 262 AutoCAD and Its Applications—Advanced Exercise 10-12 www.g-wlearning.com/CAD/ Complete the exercise on the companion website. Extracting Curves from Surfaces Creating the underlying wireframe geometry required in surface or solid modeling can sometimes be diffi cult. When working with curved surfaces, it may help to create a profi le based on the contours of an existing model. The SURFEXTRACTCURVE command allows you to extract isoline curves from an existing surface in the local U and V directions of the surface. Surface curves can be extracted from a surface model, solid model, or face of a solid. This provides a way to experiment with wire- frame geometry and get a better idea of what the resulting model will look like. The SURFEXTRACTCURVE command creates objects such as lines, circles, arcs, polylines, and splines, depending on the existing model. Once the new curves are created, the designer can use the geometry for model edits or conceptual design purposes. To extract isoline curves from an existing model, enter the SURFEXTRACTCURVE command and select a surface. An isoline curve matching the surface contour appears attached to the crosshairs. You can move the crosshairs to other surfaces to preview different curves. The default direction for the curve extraction is in the U direction. You can change the direction to the V direction by selecting the Direction option. Move the crosshairs until you locate the desired curve and pick to create the new curve. In Figure 10-29A, a curve is extracted along the U direction of the surface. In Figure 10-29B, the direction is changed to the V direction. The Chain option is used to extract curves from a “chain” of adjacent surfaces. In Figure 10-30A, the Direction option is used to change the default direction and the Chain option is used to extract a chain of three curves from the adjacent surfaces of the cell phone case surface model. Notice the curves run the total length of the cell phone case. In Figure 10-30B, the same direction is used and the Chain option is set to No to extract a curve from the top surface only. SURFEXTRACTCURVE Ribbon Surface Curves Extract Isolines Type SURFEXTRACTCURVE A B Figure 10-28. A—These six surfaces form a watertight volume. B—The solid is sculpted using the SURFSCULPT command.