返回封闭二维多段线图元的质心.
(dos_plinecentroid entity)
entity
封闭二维多段线的图元名.
如果成功, 返回质心.
nil 失败时.
Command: (dos_plinecentroid (car (entsel "\nSelect a closed curve:")))
(35.8886 26.6375 0.0)