获取图元包围盒中心点

输入list，返回一个point3d类型的list 

 public static List<Point3d > GetboxsCenter(List<Entity> ents)
 {
     
     List<Point3d> pts = new List<Point3d>();
     foreach (var item in ents)
     {
         double minx = item.Bounds.Value.MinPoint.X;
         double miny = item.Bounds.Value.MinPoint.Y;
         double maxx = item.Bounds.Value.MaxPoint.X;
         double maxy = item.Bounds.Value.MaxPoint.Y;
         Point3d pt = new Point3d((minx + maxx) / 2, (miny + maxy) / 2,0);
         pts.Add(pt);
     } 
     return pts;
 }