Sketcher "Увеличение кратности узлов"

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This page is a translated version of the page Sketcher BSplineIncreaseKnotMultiplicity and the translation is 40% complete.
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Sketcher BSplineIncreaseKnotMultiplicity.svg Увеличение кратности узлов

Системное название
Расположение в меню
Sketch → B-сплйан инструменты эскиза → Увеличение кратности узлов
Быстрые клавиши
Представлено в версии
См. также
Показать/скрыть кратность узлов B-сплайна, Уменьшение кратности узлов


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 curves are connected to form the spline are called knots. A knot on a degree d spline with the multiplicity m means that the curve left and right to the knot has at least an equal n order derivative (called Cn continuity) whereas .
Here is a cubic spline () whose knots have the multiplicity 1. The multiplicity is indicated by the number in parentheses. The indication can be changed using the toolbar button Sketcher BSplineKnotMultiplicity.svg Show/hide B-spline knot multiplicity):

Sketcher KnotMultiplicity multiplicity1.png

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 (C0 continuity). Here is the same spline where the left's knot multiplicity was increased to 3:

Sketcher KnotMultiplicity multiplicity3.png

B-spline from above with knot multiplicity 3. A control point was moved to show that the knot has C0 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:

Sketcher KnotMultiplicity locality.png

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.


  1. Select a B-spline knot, either: