# Sketcher CreatePeriodicBSpline

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Sketcher CreatePeriodicBSpline |

Menu location |
---|

Sketch → Sketcher geometries → Create periodic B-spline |

Workbenches |

Sketcher |

Default shortcut |

G B P |

Introduced in version |

0.17 |

See also |

Sketcher B-spline |

## Description

This tool traces a periodic (closed) B-spline curve from its control points. (See this page for more info about B-splines.)

A periodic B-spline curve (in white) made from 5 points. Pictured are the control polygon in green (the straight lines connecting the red points), the weight circles in blue and the curvature comb in green. The (3) digit in the centre refers to the degree of the B-spline, and the (1) and (2) digits on the knots lying on the curve refer to their multiplicity.

## Usage

- Press the Create periodic B-spline button.
- Create a series of points by clicking in the 3D view. While the command is active, the created points are connected with straight lines, and a construction circle is created centered on each point.
- Optionally press D before terminating the input to define the degree of the B-Spline. introduced in version 0.20
- Optionally press Backspace before terminating the input to delete the last created control point. introduced in version 0.20
- Pick the first curve point, or right-click to terminate the input and generate the curve.
- Depending on preferences, the tool may remain active to trace a new curve. Right-click again to exit the command.

- 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 the control point.
- The visibility of the control polygon, the curvature comb, the degree and the knot multiplicity can be toggled on/off from the B-spline tools toolbar.
- Check out the other tools in the B-spline tools toolbar for more B-spline editing tools.

## Limitations

- Many types of constraints are not supported at this time. Only the B-spline's control points and knots can be constrained.
- Trimming and extend tools are not supported.
- The shape of a B-spline curve can only be edited by dragging one of the control points. The knots lying on the curve cannot be selected.

Sketcher

**General:**Create sketch, Edit sketch, Leave sketch, View sketch, View section, Map sketch to face, Reorient sketch, Validate sketch, Merge sketches, Mirror sketch, 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, Periodic B-pline, Polyline, Rectangle, Centered rectangle, Rounded rectangle, Triangle, Square, Pentagon, Hexagon, Heptagon, Octagon, Regular polygon, Slot, 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, Diameter, Radiam, Angle, Snell's law, Internal alignment**Constraint tools:**Toggle driving/reference constraint, Activate/deactivate constraint

**Sketcher tools:**Select unconstrained DoF, Close shape, Connect edges, Select associated constraints, Select associated geometry, Select redundant constraints, Select conflicting constraints, Show/hide internal geometry, Select origin, Select vertical axis, Select horizontal 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

**Sketcher virtual space:**Switch virtual space

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

User documentation

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