IntervalMid Property

public double Mid { get; }

Public ReadOnly Property Mid As Double
	Get

using System.Linq;
using Rhino;
using Rhino.Geometry;
using Rhino.DocObjects;
using Rhino.Commands;
using Rhino.Input;
using Rhino.Input.Custom;

namespace examples_cs
{
  public class ExtendCurveCommand : Command
  {
    public override string EnglishName { get { return "csExtendCurve"; } }

    protected override Result RunCommand(RhinoDoc doc, RunMode mode)
    {
      ObjRef[] boundary_obj_refs;
      var rc = RhinoGet.GetMultipleObjects("Select boundary objects", false, ObjectType.AnyObject, out boundary_obj_refs);
      if (rc != Result.Success)
        return rc;
      if (boundary_obj_refs == null || boundary_obj_refs.Length == 0)
        return Result.Nothing;

      var gc = new GetObject();
      gc.SetCommandPrompt("Select curve to extend");
      gc.GeometryFilter = ObjectType.Curve;
      gc.GeometryAttributeFilter = GeometryAttributeFilter.OpenCurve;
      gc.Get();
      if (gc.CommandResult() != Result.Success)
        return gc.CommandResult();
      var curve_obj_ref = gc.Object(0);

      var curve = curve_obj_ref.Curve();
      if (curve == null) return Result.Failure;
      double t;
      if (!curve.ClosestPoint(curve_obj_ref.SelectionPoint(), out t))
        return Result.Failure;
      var curve_end = t <= curve.Domain.Mid ? CurveEnd.Start : CurveEnd.End;

      var geometry = boundary_obj_refs.Select(obj=> obj.Geometry());
      var extended_curve = curve.Extend(curve_end, CurveExtensionStyle.Line, geometry);
      if (extended_curve != null && extended_curve.IsValid)
      {
        if (!doc.Objects.Replace(curve_obj_ref.ObjectId, extended_curve))
          return Result.Failure;
        doc.Views.Redraw();
      }
      else
      {
        RhinoApp.WriteLine("No boundary object was intersected so curve not extended");
        return Result.Nothing;
      }

      return Result.Success;
    }
  }
}

Imports System.Linq
Imports Rhino
Imports Rhino.Geometry
Imports Rhino.DocObjects
Imports Rhino.Commands
Imports Rhino.Input
Imports Rhino.Input.Custom

Namespace examples_vb
  Public Class ExtendCurveCommand
    Inherits Command
    Public Overrides ReadOnly Property EnglishName() As String
      Get
        Return "vbExtendCurve"
      End Get
    End Property

    Protected Overrides Function RunCommand(doc As RhinoDoc, mode As RunMode) As Result
      Dim boundary_obj_refs As ObjRef() = Nothing
      Dim rc = RhinoGet.GetMultipleObjects("Select boundary objects", False, ObjectType.AnyObject, boundary_obj_refs)
      If rc <> Result.Success Then
        Return rc
      End If
      If boundary_obj_refs Is Nothing OrElse boundary_obj_refs.Length = 0 Then
        Return Result.[Nothing]
      End If

      Dim gc = New GetObject()
      gc.SetCommandPrompt("Select curve to extend")
      gc.GeometryFilter = ObjectType.Curve
      gc.GeometryAttributeFilter = GeometryAttributeFilter.OpenCurve
      gc.[Get]()
      If gc.CommandResult() <> Result.Success Then
        Return gc.CommandResult()
      End If
      Dim curve_obj_ref = gc.[Object](0)

      Dim curve = curve_obj_ref.Curve()
      If curve Is Nothing Then
        Return Result.Failure
      End If
      Dim t As Double
      If Not curve.ClosestPoint(curve_obj_ref.SelectionPoint(), t) Then
        Return Result.Failure
      End If
      Dim curve_end = If(t <= curve.Domain.Mid, CurveEnd.Start, CurveEnd.[End])

      Dim geometry = boundary_obj_refs.[Select](Function(obj) obj.Geometry())
      Dim extended_curve = curve.Extend(curve_end, CurveExtensionStyle.Line, geometry)
      If extended_curve IsNot Nothing AndAlso extended_curve.IsValid Then
        If Not doc.Objects.Replace(curve_obj_ref.ObjectId, extended_curve) Then
          Return Result.Failure
        End If
        doc.Views.Redraw()
      Else
        RhinoApp.WriteLine("No boundary object was intersected so curve not extended")
        Return Result.[Nothing]
      End If

      Return Result.Success
    End Function
  End Class
End Namespace

from Rhino import *
from Rhino.Geometry import *
from Rhino.DocObjects import *
from Rhino.Commands import *
from Rhino.Input import *
from Rhino.Input.Custom import *
from scriptcontext import doc

def RunCommand():

  rc, boundary_obj_refs = RhinoGet.GetMultipleObjects("Select boundary objects", False, ObjectType.AnyObject)
  if rc <> Result.Success:
    return rc
  if boundary_obj_refs == None or boundary_obj_refs.Length == 0:
    return Result.Nothing

  gc = GetObject()
  gc.SetCommandPrompt("Select curve to extend")
  gc.GeometryFilter = ObjectType.Curve
  gc.GeometryAttributeFilter = GeometryAttributeFilter.OpenCurve
  gc.Get()
  if gc.CommandResult() <> Result.Success:
    return gc.CommandResult()
  curve_obj_ref = gc.Object(0)

  curve = curve_obj_ref.Curve()
  if curve == None: return Result.Failure
  b, t = curve.ClosestPoint(curve_obj_ref.SelectionPoint())
  if not b: return Result.Failure
  curve_end = CurveEnd.Start if t <= curve.Domain.Mid else CurveEnd.End

  geometry = [obj.Geometry() for obj in boundary_obj_refs]
  extended_curve = curve.Extend(curve_end, CurveExtensionStyle.Line, geometry)
  if extended_curve <> None and extended_curve.IsValid:
    if not doc.Objects.Replace(curve_obj_ref.ObjectId, extended_curve):
      return Result.Failure
    doc.Views.Redraw()
    return Result.Success
  else:
    RhinoApp.WriteLine("No boundary object was intersected so curve not extended")
    return Result.Nothing

if __name__ == "__main__":
  RunCommand()