Circle SOP
Summary[edit]
The Circle SOP creates open or closed arcs, circles and ellipses.
If two NURBS circles that are nonrational (i.e. their X and Y radii are unequal) are skinned, more isoparms may be generated than expected. This is because nonrational NURBS circles parameterise their knots based on chord length, and the Skin SOP must consolidate the total number of knots between the two circles before skinning.
To remedy this, you may want to use a Refine SOP, and unrefine the resulting skin, or better yet  before unrefining, start with the same circle and use a Primitive or Transform SOP to deform the second copy before skinning.
Parameters  Page
Primitive Type type
 ⊞  For information on the different types, see the Geometry Types Guide. Depending on the primitive type chosen, some SOP options may not apply.
 Primitive
prim

 Polygon
poly

 NURBS Curve
nurbs

 Bezier Curve
bezier

Orientation orient
 ⊞  The plane on which the circle lies.
 XY Plane
xy

 YZ Plane
yz

 ZX Plane
zx

Modify Bounds modifybounds

Radius rad
 ⊞  The Radius of the Circle in the X and Y directions.
 X
radx

 Y
rady

Center t
 ⊞  The Center of the Circle in X, Y and Z.
 X
tx

 Y
ty

 Z
tz

Order order
 If a spline curve is selected, it is built at this order.
Divisions divs
 The number of edges (points +1) used to describe the circle. This option applies to polygons and imperfect splines. The more Divisions a circle has, the smoother it looks. Using three divisions makes a triangle, four divisions a diamond, five divisions a pentagon, and so on. Also, for open arc types, the number of points will equal Divisions + 1, and for closed arc types, Divisions + 2.
Arc Type arc
 ⊞  Determines how the circle should be drawn. Applies to polygons and imperfect splines only.
 Closed
closed
 An enclosed curve.
 Open Arc
openarc
 An open curve segment.
 Closed Arc
closedarc
 An Open Arc with connecting edges to the centre resembling a slice of pie.
 Sliced Arc
slicedarc
 Same as Closed Arc, but connects every single point to the center of the circle.Same as Closed Arc, but connects every single point to the center of the circle.
Arc options are available for polygonal circles and some spline types. The difference between the choices: Open, Closed, and Slice are illustrated below for the polygonal case:
Arc Angles angle
 ⊞  The beginning and ending angles of the arc. An arc will start at the beginning angle, and proceed towards the ending angle. If beginning=0 and end=360 it will be a full circle. As a reference:
Note: The total angle can exceed 360, making multiple wraps of the circle.
beginangle

endangle

Imperfect imperfect
 This option applies only to Bezier and NURBS circles. If selected, the circles are approximated nonrational curves, otherwise they are perfect rational closed curves.
Texture Coordinates texture
 ⊞ 
 Off
off

 Face
face

Compute Normals normals

Operator Inputs
 Input 0 
SOPs 

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An Operator Family that reads, creates and modifies 3D polygons, curves, NURBS surfaces, spheres, meatballs and other 3D surface data.
A surface type in SOPs including polygon, curve (NURBS and Bezier), patch (NURBS and Bezier) and other shapes like sphere, tube, and metaball. Points and Primitives are part of the Geometry Detail, which is a part of a SOP.