[R] Arrow and text on a 3d plot

[Arturo T. De Zan]

I am currently working on surface plots (with R 2.0.1) and I want to
improve the aspect of them. Having a typical 'cow-boy hat' surface
[source: Spector (1994), p. 206]:

pts <- seq(from = -8, to = 8, length = 50)
cow <- function(x, y)
{
z <- sqrt(x^2+y^2)
sin(z)/z
}
out <- outer(pts, pts, cow)
sur <- persp(x=pts, y=pts, z=out, theta=45, phi=30)

What I exactly wanted is:

a) how to add an arrow pointing the maximum point in the surface, for
example: a short arrow starting on the maximum point, with slope 45º
and finishing near the top-edge of the plot.

b) how to add a typical text at the end of the arrow, as "this is the
maximum point", as described in the above reference.

N.B.: the author used the S function "perspp", but R does not have it.

Could anyone help me? 

Thank you very much in advance.

Arturo De Zan
PhD candidate
UPC-Universitat Politecnica de Catalunya
Barcelona, Spain.