Circle SOP

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01 CircleSOP.jpg


The Circle SOP creates open or closed arcs, circles and ellipses.

If two NURBS circles that are non-rational (i.e. their X and Y radii are unequal) are skinned, more isoparms may be generated than expected. This is because non-rational 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.

PythonIcon.png circleSOP_Class


Primitive 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
  • Polygon
  • NURBS Curve
  • Bezier Curve

Orientation - The plane on which the circle lies.

Radius / center /radx /rady /tx /ty /tz - The Radius of the Circle in the X and Y directions, and the Center of the Circle in X, Y and Z.

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 - Determines how the circle should be drawn. Applies to polygons and imperfect splines only.

  • Closed - An enclosed curve.
  • Open Arc - An open curve segment.
  • Closed Arc - An Open Arc with connecting edges to the centre resembling a slice of pie.
  • Sliced Arc - 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 - 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.

Imperfect - This option applies only to Bezier and NURBS circles. If selected, the circles are approximated non-rational curves, otherwise they are perfect rational closed curves.

Inputs / Geometry Types

Primitive, Polygon, Bezier, NURBS curves.