protected override Result RunCommand(RhinoDoc doc, RunMode mode)
    {
      m_tolerance = doc.ModelAbsoluteTolerance;
      
      // only use a custom geometry filter if no simpler filter does the job

      // only curves
      var gc = new GetObject();
      gc.SetCommandPrompt("select curve");
      gc.GeometryFilter = ObjectType.Curve;
      gc.DisablePreSelect();
      gc.SubObjectSelect = false;
      gc.Get();
      if (gc.CommandResult() != Result.Success)
        return gc.CommandResult();
      if (null == gc.Object(0).Curve())
        return Result.Failure;
      Rhino.RhinoApp.WriteLine("curve was selected");

      // only closed curves
      var gcc = new GetObject();
      gcc.SetCommandPrompt("select closed curve");
      gcc.GeometryFilter = ObjectType.Curve;
      gcc.GeometryAttributeFilter = GeometryAttributeFilter.ClosedCurve;
      gcc.DisablePreSelect();
      gcc.SubObjectSelect = false;
      gcc.Get();
      if (gcc.CommandResult() != Result.Success)
        return gcc.CommandResult();
      if (null == gcc.Object(0).Curve())
        return Result.Failure;
      Rhino.RhinoApp.WriteLine("closed curve was selected");

      // only circles with a radius of 10
      var gcc10 = new GetObject();
      gcc10.SetCommandPrompt("select circle with radius of 10");
      gc.GeometryFilter = ObjectType.Curve;
      gcc10.SetCustomGeometryFilter(CircleWithRadiusOf10GeometryFilter); // custom geometry filter
      gcc10.DisablePreSelect();
      gcc10.SubObjectSelect = false;
      gcc10.Get();
      if (gcc10.CommandResult() != Result.Success)
        return gcc10.CommandResult();
      if (null == gcc10.Object(0).Curve())
        return Result.Failure;
      RhinoApp.WriteLine("circle with radius of 10 was selected");

      return Result.Success;
    }