Extending Curves

This task explains how to lengthen a curve by extension, that is by modification of its length. Two extension modes are available. In one case, it is a positive parametric extension, or it can be an extension by addition of segments to the curve. 
Should you need to extend a surface, refer to Extending Surfaces for further information.

Open the FreeStyle_Part_21.CATPart document.

  1. Select one or more curves to be extended.
Multi-selection of curves is possible.
 

  1. Click the Extend icon .

Manipulators are displayed on the curve.
 

 

The Extend dialog box is displayed.

 

 

 
  If you go over a curve's extremity with the mouse, the manipulator becomes the master manipulator, meaning it is active at that extremity.
 

 

  1. Use the manipulators to extend the curve on both sides.
  • With the Keep segmentation option checked: use the manipulator to define the curve extension.
    When the value is positive, the last segment (defined by the arc limits) is made longer.

The distance tag displays the absolute curve distance from the extremity of the original curve.
 

  • With the Keep segmentation option unchecked: the curve is extended taking the curvature continuity of the last segment into account. This means that only this last segment can be extended.
 

If you change the mode, the new curve is computed from the original curve, not from the curve previously computed..

  1. Click OK to create the extended curve.

 

Extending Curves Using Absolute and Relative Distance Modes
 

  1. Right-click the distance tag which displays the absolute curve distance.

  2. Choose the Edit item in the contextual menu.
 

 

The Edit Box dialog box is displayed.
The manipulator becomes active and the distance tag is symbolized in green.

  1. Enter the extension value.
    Here we chose 100mm.

  2. Click Close to apply the new value.
This value is always positive.
 

 

  1. Again, right-click the distance tag.

  2. Choose the Slave item in the contextual menu.
    This option enables to apply the delta curve extension to the master manipulator and the slave manipulator.
    A symbol appears near the slave manipulator and its distance tag is symbolized in yellow.
 

 

  1. Now use the manipulators to extend the second curve.

You can see that both curves are extended with the same delta (93.432mm). The slave manipulator ''follows'' the master manipulator.
If you go over the distance tag of the slave manipulator with the mouse, it becomes active again.
 

  • You can also access these contextual menu items by clicking the distance tag and moving sequentially from one option to the other (Edit, then Slave, then Free).

  • The Free option enables to free the slave manipulator.
You can extend a trimmed 3D or 2D curve: the parameterization of the original curve is used, then the extension is calculated. When extending a 2D curve, a 3D cell is added. Therefore the extended curve is made of two or more cells.

Negative Extend
  This feature provides a quick way to have the possibility within the Extend Command to do a “negative” extend for a curve ( i.e. for instance shorten a curve by 10 mm or shorten a curve in an interactive way). In other words, with Negative Extend, curves can be shortened apart from being extended. This can be done either manually or by using the edit value option. This is only for the extend curve and not for the surface. This can be done by the following options:
  • Edge Trim: With this feature, the curve is topologically relimited and the control points of the initial curve are kept. Set the Keep segmentation as unchecked for edge trim.

  • Curve Trim: With this feature, the curve is geometrically relimited. The resulting curve has same order as initial curve. Set the Keep segmentation as checked for curve trim.