public ISketchArcObject(ISketchArc ISketchArcinstance)
 {
     ISketchArcInstance = ISketchArcinstance;
 }
        /// <summary>
        /// 获取起点
        /// </summary>
        /// <param name="arc"><see cref="ISketchArc"/> Interface</param>
        /// <returns></returns>
        public static Vector3 GetStartPoint2Ex(this ISketchArc arc)
        {
            var point = arc.GetStartPoint2() as ISketchPoint;

            return(new Vector3(point.X, point.Y, point.Z));
        }