Circle Structure 
The values used are a radius and an orthonormal frame of the plane containing the circle, with origin at the center.
The circle is parameterized by radians from 0 to 2 Pi given by
t > center + cos(t)*radius*xaxis + sin(t)*radius*yaxis
where center, xaxis and yaxis define the orthonormal frame of the circle plane.
Namespace: Rhino.Geometry
The Circle type exposes the following members.
Name  Description  

Circle(Double) 
Initializes a circle with center (0,0,0) in the world XY plane.
 
Circle(Arc) 
Initializes a circle from an arc.
 
Circle(Plane, Double) 
Initializes a circle on a plane with a given radius.
 
Circle(Point3d, Double) 
Initializes a circle parallel to the world XY plane with given center and radius.
 
Circle(Plane, Point3d, Double) 
Initializes a circle parallel to a given plane with given center and radius.
 
Circle(Point3d, Point3d, Point3d) 
Initializes a circle through three 3d points.
 
Circle(Point3d, Vector3d, Point3d) 
Initializes a circle from two 3d points and a tangent at the first point.
The start/end of the circle is at point "startPoint".

Name  Description  

BoundingBox 
Gets the circle's 3d axis aligned bounding box.
 
Center 
Gets or sets the center point of this circle.
 
Circumference 
Gets or sets the circumference of this circle.
 
Diameter 
Gets or sets the diameter (radius * 2.0) of this circle.
Diameters should be positive values.
 
IsValid 
A valid circle has radius larger than 0.0 and a base plane which is must also be valid.
 
Normal 
Gets the normal vector for this circle.
 
Plane 
Gets or sets the plane of the circle.
 
Radius 
Gets or sets the radius of this circle.
Radii should be positive values.
 
Unset 
Gets a circle with Unset components.

Name  Description  

ClosestParameter 
Gets the parameter on the circle which is closest to a test point.
 
ClosestPoint 
Gets the point on the circle which is closest to a test point.
 
DerivativeAt 
Determines the value of the Nth derivative at a parameter.
 
EpsilonEquals 
Check that all values in other are within epsilon of the values in this
 
Equals  Indicates whether this instance and a specified object are equal. (Inherited from ValueType.)  
GetHashCode  Returns the hash code for this instance. (Inherited from ValueType.)  
GetType  Gets the Type of the current instance. (Inherited from Object.)  
IsInPlane 
Evaluates whether or not this circle is coplanar with a given plane.
 
PointAt 
Circles use trigonometric parameterization:
t > center + cos(t)*radius*xaxis + sin(t)*radius*yaxis.
 
Reverse 
Reverse the orientation of the circle. Changes the domain from [a,b]
to [b,a].
 
Rotate(Double, Vector3d) 
Rotates the circle through a given angle.
 
Rotate(Double, Vector3d, Point3d) 
Rotates the circle through a given angle.
 
Rotate(Double, Double, Vector3d) 
Rotates the circle around an axis that starts at the base plane origin.
 
Rotate(Double, Double, Vector3d, Point3d) 
Rotates the circle around an axis that starts at the provided point.
 
TangentAt 
Circles use trigonometric parameterization:
t > center + cos(t)*radius*xaxis + sin(t)*radius*yaxis.
 
ToNurbsCurve 
Constructs a nurbs curve representation of this circle.
This amounts to the same as calling NurbsCurve.CreateFromCircle().
 
ToNurbsCurve(Int32, Int32) 
Create a uniform nonratonal cubic NURBS approximation of a circle.
 
ToString  Returns the fully qualified type name of this instance. (Inherited from ValueType.)  
Transform 
Transforms this circle using an xform matrix.
 
Translate 
Moves the circle.
 
TryFitCircleToPoints 
Attempt to fit a circle through a set of points.
 
TryFitCircleTT 
Try to fit a circle to two curves using tangent relationships.
 
TryFitCircleTTT 
Try to fit a circle to three curves using tangent relationships.
