Sketcher CreateBSplineByInterpolation

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Sketcher CreateBSplineByInterpolation

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


The Sketcher CreateBSplineByInterpolation tool creates a B-spline curve through knot points. See this page for more information about B-splines.


See also: Drawing aids.

  1. There are several ways to invoke the tool:
    • Press the B-spline by knots button.
    • Select the Sketcher → Sketcher geometries → Create B-spline by knots option from the menu.
    • Use the keyboard shortcut: G then B, then I.
  2. The cursor changes to a cross with the tool icon.
  3. Pick several knot points.
  4. Optionally press M before finishing the input to define the multiplicity of the last defined knot point (this may not always be respected, see limitations for details).
  5. Optionally press Backspace before finishing the input to delete the last knot point.
  6. Right-click or press Esc to finish the input.
  7. The B-spline is created, including a set of internal geometry (weight circles and knot points).
  8. 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.


See Sketcher CreateBSpline.


  • The resultant curve is no different from a (non-uniform) B-spline defined through control points. So all related limitations apply. See Sketcher CreateBSpline.
  • The created B-splines are always cubic (i.e. with degree 3).
  • The defined multiplicity may not always be respected:
    • For a periodic spline, the first knot (coincident with last) always has a multiplicity of 2.
    • For a non-periodic spline, the first and last knots always have a multiplicity of 4.
    • If the points just before and just after have multiplicities >=3, the piece between these two is fully continuous, and this (middle) point will only be constrained with point-on-object. If a knot is needed, consider using the insert knot tool.