Usage
persp.plane(x, y, z, persp.out, ...)
persp.floor(x, y, z, persp.out, ...)
persp.back.wall.x(x, y, z, persp.out, ...)
persp.back.wall.y(x, y, z, persp.out, ...)
persp.setup(...) ## persp.setup is not needed or used in R.
## persp.setup is in the "splus" Chapter in S-Plus.