The NURBS curves drawn on a surface are similar to the full 3D NURBS curves created with the curve tool and referenced across photographs. They do have some differences with full 3D Curves and they also have some differences with line-type Surface Draw. Surface Draw Curves:
• cannot be extended,
• cannot go through existing points (Object Points or other Surface Draw Points), and
• because of the method surface draw curves search for their best Surface to associate with, it is recommended that when a curve changes planes at sharp angle that the user place points close to the transition.
• Surface Draw curves have a polyline property that changes the curve shape to a set of connected straight line segments. Right click on the Surface Draw curve, then select Properties (or see Properties Pane), then check the Polyline property.
• Surface Draw curves can have ‘corner points’ which reset the curve calculation (while in the mode, right click and use the Create Corner menu item, or hold down shift while creating a point). For example, if the curve hits a corner and you don’t want that corner ‘rounded’, create a corner point to extend the curve straight in the new direction.