To Modify a Curve
1. Click > 
Modify Shape and select a curve. The Modify Curve dialog box opens.
Modify Shape and select a curve. The Modify Curve dialog box opens.2. Select one of the following curve modification options:
◦ To modify the curve using its control points, click 
and select the vertex of the control polygon to move.
and select the vertex of the control polygon to move.◦ To modify the curve using its interpolation points, click 
and click one of the following:
and click one of the following:▪ Move—Moves the curve by moving the interpolation points on the curve using the movement options.
▪ Add—Adds interpolation points to the curve at the selected location.
▪ Delete—Deletes the interpolation points from the curve by selecting points.
▪ Redistribute—Redistributes the interpolation points according to the curve’s curvature.
3. Optionally, specify the movement options. The available movement options are:
◦ Curve plane—Restricts the curve movement to the curve plane only. A curve plane is a plane formed by the tangent and the normal vector of the curve.
◦ 3D movement—Moves the curve freely in 3D space. This option is not available for curve on facets or curve on surface.
◦ Local—Moves only the selected control point.
◦ Smooth region—Moves the control points by a distance relative to the selected point. The point movement distance decreases proportional to its distance from the selected point by a cubic law.
◦ Linear region—Moves the control points by a distance relative to the selected point. The point movement distance decreases proportional to its distance from the selected point by a linear law.
◦ Constant region—Moves all the control points by the same distance from the selected point. For a constrained surface, the boundary does not move.
4. Select and drag a vertex of the control polygon or the interpolation points to modify the curve. Instead of dragging, you can specify the following if finer control of point movement is required.
◦ Normal direction—Specifies the increment in the normal direction.
◦ Tangent direction—Specifies the increment in the tangent direction.
◦ Bi-normal direction—Specifies the increment in the binormal direction. This option is not available for curve on facets or curve on surface.
◦ Increment—Specifies the value of the point movement increment.
5. Click OK.