Curve Edit > Project Tangent

Allows for the modification of a curve or surface edge to achieve tangency or curvature continuity with a surface, or tangency with a curve intersection.

Project tangent allows align construction history on the same curve if the two are modifying a different end of the curve.

It does not, however, allow other types of history to be modifying the same curve. For example, if blend curve or symmetry plane align history exist on the curve you want to modify, a confirmation box displays asking whether history can be deleted.

See Make a curve tangent or curvature continuous with a surface.

Project Tangent Adjustment Options

Tangent Adjustment

Scale: This scale factor adjusts the length of the tangent vector, without modifying its direction.
Rotation: The degree of rotation in the tangent plane. A rotation of 0 gives the default projection heading. Use positive and negative numbers to rotate in different directions.

The following option is available only when Transform Control is set to Tangent.

Tangent Angle: The degree of rotation out of the tangent plane. An angle of 0 gives the default projection pitch (that is tangent continuity). Use positive and negative numbers to rotate in different directions. Changing this value removes tangent continuity.

The following option is only available when Transform Control is set to Curvature.

Curvature: The magnitude of the curvature modification. Modify the shape of the curve without changing the curvature at the join with the surface.

Xform Control menu

Tangent: Create tangent continuity between the surface/intersection and the curve.

This option is not available when you project from a curve intersection, or when Tangent Align is set to Normal.

Curvature: Create curvature continuity between the surface and the curve.

Region Control menu

This menu has no functionality. It contains only one item, indicating the number of CVs that the tool modifies (equal to the curve degree plus one).

If the curve is modified at its endpoint, only two CVs are affected for tangent continuity and only three for curvature (and this menu value is ignored).

Tangent Align menu

U/V: Project the tangent onto the U or V direction of the surface.

This option disables Curvature in the Transform Control menu.

Normal: Project the tangent onto the surface’s normal at the edge, making the curve perpendicular to the surface, instead of tangent. It is equivalent to a Tangent Angle of 90.0 degrees.
Reverse: Reverse the direction of the current tangent vector.

Note
The U, V, and Normal commands set the type of alignment. The Reverse command reverses the current tangent direction, but does not change the type of alignment.

Control Tools menu

Undo: Reverses all changes to the curve by the Project Tangent tool.

This option is the same as using Edit > Undo.
Next Crv: Keep changes to the current curve and pick another curve to modify.
Done: Keep changes to the current curve and close the Adjustment control window.