When working with surfaces you may want to create non-mesh wireframes displaying the contours of a surface to experiment with and regenerate variations. Objects created by this process can be lines, plines, splines, or arcs, depending on the surface, solid, or face from which they are extracted and the command remains active until you press Enter.
After modifying extracted curves, use the LOFT command to regenerate a surface that passes through the extracted objects.
The direction option allows you to extract curves in the other direction. Isoline curves are extracted in the U direction, by default.
Choose the spline points option to extract a spline that passes through all specified points on the surface.