# Sketcher CreateBSplineByInterpolation

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 CreatePeriodicBSplineByInterpolation |

## Description

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

## Usage

See also: Drawing aids.

- 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.

- The cursor changes to a cross with the tool icon.
- Pick several knot points.
- 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).
- Optionally press Backspace before finishing the input to delete the last knot point.
- Right-click or press Esc to finish the input.
- The B-spline is created, including a set of internal geometry (weight circles and knot points).
- If the tool runs in continue mode:
- Optionally keep creating B-splines.
- To finish, right-click or press Esc, or start another geometry or constraint creation tool.

## Notes

## 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.

Sketcher

**General:**Create sketch, Edit sketch, Map sketch to face, Reorient sketch, Validate sketch, Merge sketches, Mirror sketch, Leave sketch, View sketch, View section, Toggle grid, Toggle snap, Configure rendering order, Stop operation

**Sketcher geometries:**Point, Line, Arc, Arc by 3 points, Circle, Circle by 3 points, Ellipse, Ellipse by 3 points, Arc of ellipse, Arc of hyperbola, Arc of parabola, B-spline by control points, Periodic B-spline by control points, B-spline by knots, Periodic B-spline by knots, Polyline, Rectangle, Centered rectangle, Rounded rectangle, Triangle, Square, Pentagon, Hexagon, Heptagon, Octagon, Regular polygon, Slot, Fillet, Corner-preserving fillet, Trim, Extend, Split, External geometry, Carbon copy, Toggle construction geometry

**Sketcher constraints:****Geometric constraints:**Coincident, Point on object, Vertical, Horizontal, Parallel, Perpendicular, Tangent, Equal, Symmetric, Block**Dimensional constraints:**Lock, Horizontal distance, Vertical distance, Distance, Radius or weight, Diameter, Auto radius/diameter, Angle, Refraction (Snell's law)**Constraint tools:**Toggle driving/reference constraint, Activate/deactivate constraint

**Sketcher tools:**Select unconstrained DoF, Select associated constraints, Select associated geometry, Select redundant constraints, Select conflicting constraints, Show/hide internal geometry, Select origin, Select horizontal axis, Select vertical axis, Symmetry, Clone, Copy, Move, Rectangular array, Remove axes alignment, Delete all geometry, Delete all constraints

**Sketcher B-spline tools:**Show/hide B-spline degree, Show/hide B-spline control polygon, Show/hide B-spline curvature comb, Show/hide B-spline knot multiplicity, Show/hide B-spline control point weight, Convert geometry to B-spline, Increase B-spline degree, Decrease B-spline degree, Increase knot multiplicity, Decrease knot multiplicity, Insert knot, Join curves

**Sketcher virtual space:**Switch virtual space

**Additional:**Sketcher Dialog, Preferences, Sketcher scripting

User documentation

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