About Curve Constraints
You can click > 
Align on the Import DataDoctor tab to create or modify curve constraints. You can apply the following types of constraints on curves:
Align on the Import DataDoctor tab to create or modify curve constraints. You can apply the following types of constraints on curves:• Position—A curve is constrained by position if the end of the curve is constrained to a point on another curve, vertex, or a surface. This is the default.
• Tangent—Sets the tangent of the secondary curve to match the tangent value of the primary curve.
• Curvature—Same as Tangent, but the original curvature value of the primary curve is also maintained.
• Normal—Sets the curve normal to the selected reference.
 | Constraints are automatically deleted if you delete the constrained curve, target curve, or surface. |