If IsClosed, just return true. Otherwise, decide if curve can be closed as follows: Linear curves polylinear curves with 2 segments, Nurbs with 3 or less control points cannot be made closed. Also, if tolerance > 0 and the gap between start and end is larger than tolerance, curve cannot be made closed. Adjust the curve's endpoint to match its start point.

Namespace: Rhino.Geometry
Assembly: RhinoCommon (in RhinoCommon.dll) Version: Rhino 6.0

C#

public bool MakeClosed(
	double tolerance
)

VB

Public Function MakeClosed ( 
	tolerance As Double
) As Boolean

tolerance

Type: System.Double
If nonzero, and the gap is more than tolerance, curve cannot be made closed.

Type: Boolean
true on success, false on failure.

Supported in: 6.0.16224.21491, 5D58w

Curve Class
Rhino.Geometry Namespace