Editing Splines in AutoCAD

You can delete fit points of a spline, add fit points for greater accuracy, or move fit points to alter the shape of a spline. You can open or close a spline and edit the spline start and end tangents. Spline direction is reversible. You can change the tolerance of the spline also. Tolerance refers to how closely the spline fits the set of fit points you specify. The lower the tolerance, the more closely the spline fits the points.

You can refine a spline by increasing the number of control points in one portion of the spline or by changing the weight of specific control points. Increasing the weight of a control point pulls the spline more towards that point. You can also refine a spline by changing its order. A spline’s order is the degree of the spline polynomial + 1. A cubic spline, for example, has order 4. The higher a spline’s order, the more control points it has.

Consider the following example. You have created a spline to represent a geographic contour. Grips are turned on, and you need to move the fourth fit point to increase accuracy. When you select the spline, grips appear at the control points. If you created the spline by fitting it through a set of points, and you haven’t purged this information using the Purge option of the SPLINEDIT command, and you select the Fit Data option, grips appear at the fit points on the selected spline instead of at the control points.


To move a spline fit point

  1. From the Modify menu, choose Object Spline.
  2. Select the spline.
  3. Enter f (Fit Data).
  4. Enter m (Move Vertex).
  5. Repeatedly enter n (Next) to select the next vertex until you get to the highlighted control point that you want to move.
  6. Move the vertex with the pointing device or by entering the coordinate of the new location.
  7. Enter x three times to exit the command.


If any three consecutive control points are located at the same position, bad data is created. In this situation, it is not possible to calculate a tangent at that position. AutoCAD can only offset curves that have a nonzero-length tangent vector at each point.

Command line SPLINEDIT
Shortcut menu Select the spline to modify, right-click in the drawing area, and choose Spline Edit.

1 comment so far ↓

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