Wolfram Function Repository
Instantuse addon functions for the Wolfram Language
Function Repository Resource:
Generate a BSplineCurve primitive representing a circle
ResourceFunction["SplineCircle"][{x,y}, r] returns a BSplineCurve representation of a 2D circle with center {x,y} and radius r. 

ResourceFunction["SplineCircle"][{x, y}, {r_{1},r_{2}}] returns a 2D ellipse with semimajor axis r_{1} and semiminor axis r_{2}, and with the semimajor axis in the x direction. 

ResourceFunction["SplineCircle"][{x, y}, {r_{1},r_{2}}, u] returns a 2D ellipse with the semimajor axis in the direction u. 

ResourceFunction["SplineCircle"][{x, y}, {r_{1},r_{2}}, u, {θ_{1}, θ_{2}}] returns a 2D elliptical arc from θ_{1} to θ_{2} measured from the semimajor axis. 

ResourceFunction["SplineCircle"][{x, y, z}, r] returns a BSplineCurve representation of a 3D circle with center {x,y,z} and radius r, with the symmetry axis in the z direction. 

ResourceFunction["SplineCircle"][{x, y, z},{r_{1},r_{2}}] returns a 3D ellipse with semimajor axis r_{1} and semiminor axis r_{2}, and with the semimajor axis in the x direction. 

ResourceFunction["SplineCircle"][{x, y, z},{r_{1},r_{2}}, a] returns a 3D ellipse with the symmetry axis in the direction a. 

ResourceFunction["SplineCircle"][{x, y, z}, {r_{1},r_{2}}, {u, v}] returns a 3D ellipse with the semimajor axis in the direction u, and with the elliptical plane being spanned by u and v. 

ResourceFunction["SplineCircle"][{x, y, z},{r_{1},r_{2}}, p, {θ_{1}, θ_{2}}] returns a 3D elliptical arc in the plane specified by p, where p can be the symmetry axis or the plane spanned by 3D vectors u and v. 
A 2D circle:
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A 2D elliptical arc:
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A 2D ellipse with semimajor axis in the direction {4, 1}:
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Differently styled ellipses:
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A 3D circle:
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A 3D ellipse:
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A 3D elliptical arc:
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Use SplineCircle as a FilledCurve specification:
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Use SplineCircle as a Tube curve specification:
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Use SplineCircle as an Arrow curve specification:
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Rendering of a fairly large number of circle tubes:
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A 2D SplineCircle with a nondefault semimajor axis is equivalent to a geometric transformation of a Circle object:
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The Circle equivalent:
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When only a symmetry axis {x,y,z} is specified, the largest component of the symmetry axis is computed, and the third coordinate starting with the largest component in a RHS is determined. Then the semimajor axis is assumed to be perpendicular to both the third component and the symmetry axis. For example, suppose the symmetry axis is:
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The largest component is in the z direction, and so the third coordinate would be the y coordinate. Then the semimajor axis is assumed to be in the direction:
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Check:
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