说明：  DXF文件输出接口.提供类似标准绘图指令,用户利用这些指令,可以写出能够被 ACAD或CorelDraw读入的标准DXF文件.
(DXF files output interface. Similar standards for graphics instructions, users of these instructions, it can be ACAD write or read CorelDraw standard DXF files.)