Inserting connecting curves - Control points mode

To accomplish this task, open file "connect.e3".

1 After starting the Connect Curve command, click on the first and on the second curve close to the end points to connect.



To change the selected curves right-click, select Reset Current Selection and perform selection again.

2 Set the Edit Mode drop-down list to Control points (if not already set so). A preview of the blending curve along with its control points is displayed:



You can drag the control points corresponding to the endpoints of the connecting curve along the original curves.



You can also move the other control points of the blending curve as you like, as long as you haven't set any constraints upon them:



A set of constraints to be applied to control points is available by expanding the Constraints node (see Setting constraints on Control Points). For example, you can control the distribution of the control point motion by properly setting the Distribution law options (see Using the Distribution law options for details).

Snap to Markers
When the Snap to Markers check box is selected under More Options, you will be enabled to move a control point snapping it exactly to another one, which is not possible when the check box is not selected.


3 You can set the same continuity conditions at both endpoints of the blending curve, or different conditions at each endpoint. To set the same conditions, select the Same continuity check box. To set different conditions, uncheck the box: a separate Continuity By drop-down list will show up at each endpoint.



Suppose you have checked the Same continuity box. Only one drop-down list will be available in the selection list. The default value is Tangency, but you can set continuity to each of the following Continuity Types (continuity conditions will be enforced by moving individual control points the minimum distance required):
Position specifies that only geometric continuity is required at the endpoints.
Tangency specifies that the blending curve must share the same tangent line as the parent curve at the given end.
Curvature specifies that the blending curve must have the same value of curvature as the parent curve at the given end.
Torsion specifies that the blending curve must have the same value of torsion as the parent curve at the given end.
Smooth curvature specifies that the parent curve's curvature plot and the blending curve's curvature plot must be tangent continuous at the specified end.
Curvature plot curvature specifies that the parent curve's curvature plot and the blending curve's curvature plot must be curvature continuous at the specified end.

By selecting the Curve Curvature command you can also display a curvature plot which will help you check the shape and the smoothness of the resulting curve.
4 By selecting the options of the Result drop-down list you can specify what kind of result you want to obtain:
Connect curve only the only result of the command will be the connecting curve.
Split original curves the result of the command will be curves split from the original curves in addition to the connecting curve. These curves will join the connecting curve with the specified continuity at their ends. Thus, the maximum number of curves you will obtain with this option is three.
Join original curves the result will be a single curve made of the connecting curve and the two curves derived from the original ones according to the chosen endpoints and to the specified continuity conditions.
A Hide check box shows up when the Split original curves or Join original curves options are selected: when checked, the original curves will be hidden as soon as the connecting curve is created.
When Join original curves is selected, three further additional options are available:
Max. No. arcs specifies the maximum number of arcs (parametric spans) you want the resulting curve to be composed of.
Max. Degree specifies the maximum degree to use in the resulting joined curve.
Tolerance specifies the tolerance for the resulting joined curve, which is an Euclidean space tolerance for the parameter equal distance between the resulting joined curve and the original parent and blending curves.
5 In the Default drop-down list under More Options you can choose the type of construction for the connecting curve. Please note that changing the Default mode will cause prior manipulation of individual control points to be lost.
Single arc produces a single arc curve (a Bezier control point curve) with a degree determined by the specified geometric continuity conditions at the endpoints.
Minimum degree produces a NURBS curve with multiple arcs. The degree — at least three — will be the minimum necessary to maintain the specified geometric continuity conditions both internally and at the endpoints.
6 You can increase the degree of the blending curve by using the Increase degree button under More Options. The degree of the curve is raised by one for each button press. The shape of the curve will remain unchanged.
  • In Single arc mode, a single new control point will be added for each Increase degree button press.
    first click second click
  • In Minimum degree mode, a single new control point will be added for each arc (parametric span) of the curve.
     
To decrease the curve degree, press Decrease degree. The degree of the curve is lowered by one for each button press. If the blending curve is already at a minimum degree for the specified constraints, the degree will not be lowered further.

Reset
The Reset button will compute the blending curve resulting from the specified geometric continuity at each endpoint and the setting of the Default mode (Single arc or Minimum degree).
Hitting this button has no effect on prior control point manipulations.

 
7 Click or to confirm your selections and create the curve (s). In the following illustration you can see the curve obtained setting the Result to Connect curve only, continuity conditions to Tangency and Weight to 1 at both endpoints.



Click to discard your changes.
Blend Curve
Tips and Tricks