Skip to content

Latest commit

 

History

History
48 lines (29 loc) · 3 KB

Sketcher_BSplineIncreaseKnotMultiplicity.md

File metadata and controls

48 lines (29 loc) · 3 KB
Raw
  • GuiCommand: Name: Sketcher BSplineIncreaseKnotMultiplicity MenuLocation: Sketch -> Sketcher B-spline tools -> Increase knot multiplicity Workbenches: Sketcher_Workbench Version: 0.17 SeeAlso: Sketcher_BSplineKnotMultiplicity, Sketcher_BSplineDecreaseKnotMultiplicity

Sketcher BSplineIncreaseKnotMultiplicity

Description

Increases the multiplicity of a B-spline knot. (See this page for more info about B-splines).

B-splines are basically a combination of Bézier curves (nicely explained in this and this video). The points where two Bézier pieces are connected are called knots. A knot on a spline with degree d and with the multiplicity m means that the curve left and right to the knot has at least an equal n order derivative (called C^n^ continuity) whereas $n=d-m$. Here is a cubic spline ($d=3$) whose knots have the multiplicity 1. The multiplicity is indicated by the number in parentheses. The indication can be changed using the toolbar button [ Show/hide B-spline knot multiplicity:

*B-spline where both knots have the multiplicity 1.*

A multiplicity of 3 will change this spline so that even the first order derivatives are not equal (C^0^ continuity). Here is the same spline where the left's knot multiplicity was increased to 3:

*B-spline from above with knot multiplicity 3. A control point was moved to show that the knot has ''C''0 continuity.*

A consequence of a higher multiplicity is that for the price of loosing continuity you gain local control. This means the change of one control point only affects the spline locally to this changed point. This can be seen in this example, where the spline from the first image above was taken and its second control point from the right side was moved up:

*Effect of locality due to different multiplicity.*

One can see that the spline with knot multiplicity 1 is completely changed while the one with multiplicity 2 kept its form at its left side.

Usage

  1. Select a B-spline knot, either:
    • Press the button [ Increase knot multiplicity.
    • Use the menu Sketch → Sketcher B-spline tools → [ Increase knot multiplicity.

{{Sketcher_Tools_navi}}

⏵ documentation index > Sketcher > Sketcher BSplineIncreaseKnotMultiplicity