Adding stippling to image/contour plot
===

have some data that I would like to add "stippling" to show where it is "important", as they do in the IPCC plots (see http://www.ipcc.ch/graphics/ar4-wg1/jpg/fig-10-18.jpg).

At the moment I am really struggling with trying to do this in R. 

If I make up some test data and plot it:

>> data <- array(runif(12*6), dim=c(12,6) )

>> over <- data

>> over[over>0.6] <- NA

>> image(1:12, 1:6, data)

What I would like to finally do is over-plot some points based on the array "over" on top of the current image.

Any suggestions!??

Thanks!
