library(rgl)
persp3d(c(0,0.001), c(0,0.001), matrix(0, 2, 2), color='white', alpha=0, xlim=c(-3,3), ylim=c(-3,3), zlim=c(-1,1), xlab='N1', ylab='N2', zlab='S', forceClipregion = TRUE, box=FALSE)
triangles3d(c(0,3,0), c(0,0,3), c(0,1,1), color='lightgray')
triangles3d(c(0,3,0), c(0,0,-3), c(0,1,1), color='lightgray')
triangles3d(c(0,-3,0), c(0,0,3), c(0,1,1), color='lightgray')
triangles3d(c(0,-3,0), c(0,0,-3), c(0,1,1), color='lightgray')
triangles3d(c(0,3,0), c(0,0,3), c(0,-1,-1), color='lightgray')
triangles3d(c(0,3,0), c(0,0,-3), c(0,-1,-1), color='lightgray')
triangles3d(c(0,-3,0), c(0,0,3), c(0,-1,-1), color='lightgray')
triangles3d(c(0,-3,0), c(0,0,-3), c(0,-1,-1), color='lightgray')