addradialdimension

          
using Rhino;
using Rhino.DocObjects;
using Rhino.Commands;
using Rhino.Geometry;
using Rhino.Input;

namespace examples_cs
{
  public class AddRadialDimensionCommand : Rhino.Commands.Command
  {
    public override string EnglishName
    {
      get { return "csAddRadialDimension"; }
    }

    protected override Result RunCommand(RhinoDoc doc, RunMode mode)
    {
      ObjRef obj_ref;
      var rc = RhinoGet.GetOneObject("Select curve for radius dimension", 
        true, ObjectType.Curve, out obj_ref);
      if (rc != Result.Success)
        return rc;
      double curve_parameter;
      var curve = obj_ref.CurveParameter(out curve_parameter);
      if (curve == null)
        return Result.Failure;

      if (curve.IsLinear() || curve.IsPolyline())
      {
        RhinoApp.WriteLine("Curve must be non-linear.");
        return Result.Nothing;
      }

      // in this example just deal with planar curves
      if (!curve.IsPlanar())
      {
        RhinoApp.WriteLine("Curve must be planar.");
        return Result.Nothing;
      }

      var point_on_curve = curve.PointAt(curve_parameter);
      var curvature_vector = curve.CurvatureAt(curve_parameter);
      var len = curvature_vector.Length;
      if (len < RhinoMath.SqrtEpsilon)
      {
        RhinoApp.WriteLine("Curve is almost linear and therefore has no curvature.");
        return Result.Nothing;
      }

      var center = point_on_curve + (curvature_vector/(len*len));
      Plane plane;
      curve.TryGetPlane(out plane);
      var radial_dimension = 
        new RadialDimension(center, point_on_curve, plane.XAxis, plane.Normal, 5.0);
      doc.Objects.AddRadialDimension(radial_dimension);
      doc.Views.Redraw();
      return Result.Success;
    }
  }
}