Sketcher CreateBSpline

From FreeCAD Documentation

Sketcher CreateBSpline

Menu location
Sketch → Sketcher geometries → Create B-spline
Default shortcut
Introduced in version
See also
Sketcher CreatePeriodicBSpline


The Sketcher CreateBSpline tool creates a B-spline curve from control points. See this page for more information about B-splines.

B-spline curve (white) defined by 5 control points.
The control polygon (green) connects the control points (marked with dark yellow weight circles).
The number 3 (green, without brackets) in the center refers to the degree of the B-spline.
The numbers (1) and (4) (green, in round brackets) refer to the multiplicity of the knot points.
The numbers [1.00] (green, in square brackets) refer to the weights of the control points.


See also: Drawing aids.

  1. There are several ways to invoke the tool:
  2. The cursor changes to a cross with the tool icon.
  3. Pick several control points.
  4. While the tool is active a small construction circle is created centered on each point.
  5. Optionally press D before finishing the input to define the degree of the B-spline.
  6. Optionally press Backspace before finishing the input to delete the last control point.
  7. Right-click or press Esc to finish the input.
  8. The B-spline is created, including a set of internal geometry (weight circles and knot points).
  9. If the tool runs in continue mode:
    1. Optionally keep creating B-splines.
    2. To finish, right-click or press Esc, or start another geometry or constraint creation tool.


  • Elements of the internal geometry can be deleted. They can be recreated at any time with Sketcher RestoreInternalAlignmentGeometry.
  • After a B-spline is created, it is possible to define the weight of the control points by changing the radii of the weight circles. The equality constraints on the circles need to be deleted first. The radius constraint is arbitrary, the weight of the control points will be defined by the relative radii of the circles. It works similar to gravity: the bigger a circle is in relation to the others, the more the curve will be attracted to that control point.
  • The visibility of the degree, the control polygon, the curvature comb, the knot multiplicity and the control point weight can be toggled on/off from the Sketcher visual toolbar.


  • Several constraints are not supported at this time.