Sketcher BSplineIncreaseDegree

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Revision as of 02:55, 1 November 2020 by Uwestoehr (talk | contribs) (proper explanation, step 1)
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Sketcher BSplineIncreaseDegree.svg Sketcher BSplineIncreaseDegree

Menu location
Sketch → Sketcher B-spline tools → Increase Degree of B-spline
Workbenches
Sketcher
Default shortcut
None
Introduced in version
0.17
See also
Show/hide B-spline degree, Decrease B-spline degree


Description

Increases the degree of the B-spline(see B-spline).

B-splines are basically a combination of Bézier curves (nicely explained in this and this video). These curves have degree - 1 control points.
In this cubic spline (degree 3) there are 3 segments, meaning 3 curves are connected at 2 knots
(degree is indicated by the number, indication can be changed using the toolbar button Sketcher BSplineDegree.svg Show/hide B-spline degree):

Sketcher BSplineDegree3.png

B-spline with degree 3 and 2 knots that each have the multiplicity 1.


The outer segments have each 2 control points, the inner one none to fulfill the constraint that the knots have multiplicity 1. (see this page for an explanation of the multiplicity)

Increasing the degree will not delete control points but try instead to conserve the shape of the spline. Therefore segments will be added. For our example you see a lot of new spline segments with each one control point and the shape of the spline has only slightly been changed:

Sketcher BSplineDegree4.png

Same B-spline where the degree was changed from 3 to 4. Note that also the knot multiplicity was increased to conserve the spline shape.


If you take this result and decrease the degree, you cannot get the initial state of the spline because information was lost by the increase of the degree. For our example increasing the degree again leads to this:

Sketcher BSplineDegree3from4.png

Same B-spline where the degree was again changed from 4 to 3. Note that the knot multiplicity was not decreased but increased.

Usage

  1. Select an edge from an existing B-spline, and press Sketcher BSplineIncreaseDegree.svg Increase B-spline degree.