Draws a 3D cross or axis vectors in an rgl scene.
cross3d(centre = rep(0, 3), scale = rep(1, 3), ...)
A scalar or vector of length 3, giving the centre of the 3D cross
A scalar or vector of length 3, giving the lengths of the arms of the 3D cross
Other arguments, passed on to
Used for its side-effect, but returns (invisibly) a 6 by 3 matrix containing the end-points of three axes, in pairs.