站长说的很对，补充一下： w6 .HvH-@?
Normal Vector v0sX'>f
The Normal Vector is a vector in 3D space that is used to orient the projection kA0 ^~
plane for the irradiance map. The plane is defined to be perpendicular to the x.RZ!V-
Normal Vector, and the irradiance incident on the selected surface is projected 6qf`P!7d]M
onto this plane. When the map is displayed, the normal vector is pointing toward / [M~##%:
you. &I= q%
Up Vector E{J;-+t
The Up Vector is a vector in 3D space that is used to orient the projection plane c,^-nH'X>
for the irradiance map. The plane is defined so that the Up Vector is parallel to the kOO2 ?L|Z
vertical side of the plane. The irradiance incident on the selected surface is $Izk]o;X~
projected onto this plane. When the map is displayed, the up vector will point E~ kmU{D
toward the top of the screen.
