[R] xyplot ontop a contourplot (package: lattice)

[Jay]

Hello,

I have a contourplot plot that shows the data I want. However, I would
like to point a certain amount of points from this plot via a
xyplot().

Example:

x <- seq(pi/4, 5 * pi, length.out = 100)
y <- seq(pi/4, 5 * pi, length.out = 100)
r <- as.vector(sqrt(outer(x^2, y^2, "+")))
grid <- expand.grid(x=x, y=y)
grid$z <- cos(r^2) * exp(-r/(pi^3))
levelplot(z~x*y, grid, cuts = 50, panel.xyplot(x~y))


But the point does not show up. What is the correct way to achieve
this?