[ARX程序]：请教AutoCAD中图形的定义问题

sleeptiger

就是AutoCAD中怎样定义图形？有什么数据？如果是参数定义，参数方程和参数是如何设置的？
比如：我创建了一个球，球心在（0，0，0），半径为100，应用Brep的例程brdump观察，结果如下：
Command: brdump
Select No Validation vs. Full Validation: None/<Full>: f
Enter Subent Type: Edge/Face/<Brep>: f
Pick a face
Surface Type: Sphere
Surface Definition Data Begin:
Sphere centre is (0.000000 , 0.000000 , 0.000000 )
Sphere radius is 100.000000
Sphere start angle in U is -1.570796
Sphere end angle in U is 1.570796
Sphere start angle in V is -3.141593
Sphere end angle in V is 3.141593
Sphere north pole is (0.000000 , 0.000000 , 100.000000 )
Sphere south pole is (0.000000 , 0.000000 , -100.000000 )
Surface Definition Data End
Surface Evaluation Begin:
Parameter space bounds are ((-1.570796, 1.570796 ), (
-3.141593, 3.141593 ))
Parameter space mid-range is ( 0.000000, 0.000000 )
Point on surface is (100.000000 , 0.000000 , 0.000000 )
Surface Evaluation End
Surface Orientation
为什么有surface definition data和surface evaluation 的parameter space
我试着切割该球，U、V的范围和参数范围有变化，不知怎样得到形体的定义数据，并且可以通过该数据人工的复原该形体？
请教高人指点，谢谢！！！