Sketcher CreateBSplineByInterpolation

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Sketcher CreateBSplineByInterpolation

Menu location
Sketch → Sketcher geometries → Create B-spline by knots
Workbenches
Sketcher
Default shortcut
G B I
Introduced in version
0.21
See also
Sketcher Periodic B-spline

Description

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

Usage

  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 white cross with the tool icon.
  3. Pick several knot points.
  4. Optionally press M before terminating the input to define the multiplicity of the last defined knot point (note that this may not always be respected, see limitations for details).
  5. Optionally press Backspace before terminating the input to delete the last knot point.
  6. Right-click or press Esc to terminate the input.
  7. The B-spline is created, including a set of internal geometry (weight circles and knot points)...
  8. Optionally deleted one or more elements of this internal geometry. They can be recreated at any time with Sketcher RestoreInternalAlignmentGeometry...

Notes

See Sketcher CreateBSpline.

Limitations

  • 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.