About Curve Constraints
You can click Edit > 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.