extractisocurve

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

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

    protected override Result RunCommand(RhinoDoc doc, RunMode mode)
    {
      ObjRef obj_ref;
      var rc = RhinoGet.GetOneObject("Select surface", false, ObjectType.Surface, out obj_ref);
      if (rc != Result.Success || obj_ref == null)
        return rc;
      var surface = obj_ref.Surface();

      var gp = new GetPoint();
      gp.SetCommandPrompt("Point on surface");
      gp.Constrain(surface, false);
      var option_toggle = new OptionToggle(false, "U", "V");
      gp.AddOptionToggle("Direction", ref option_toggle);
      Point3d point = Point3d.Unset;
      while (true)
      {
        var grc = gp.Get();
        if (grc == GetResult.Option)
          continue;
        else if (grc == GetResult.Point)
        {
          point = gp.Point();
          break;
        }
        else
          return Result.Nothing;
      }
      if (point == Point3d.Unset)
        return Result.Nothing;

      int direction = option_toggle.CurrentValue ? 1 : 0; // V : U
      double u_parameter, v_parameter;
      if (!surface.ClosestPoint(point, out u_parameter, out v_parameter)) return Result.Failure;

      var iso_curve = surface.IsoCurve(direction, direction == 1 ? u_parameter : v_parameter);
      if (iso_curve == null) return Result.Failure;

      doc.Objects.AddCurve(iso_curve);
      doc.Views.Redraw();
      return Result.Success;
    }
  }
}