[R] Creating smooth color regions with panel.contourplot()

[Waichler, Scott R]

Thank you very much, Deepayan.  There is just one more feature I'd like
to get, the ability to add the contour lines.  My revision to your code
below prints too many lines.  What needs to be changed?  

--Thanks,
Scott Waichler
scott.waichler at pnl.gov

library(gridBase)
library(lattice)
data(volcano)

panel.filledcontour <- function(x, y, z, subscripts, at, col.regions =
cm.colors,
                                col = col.regions(length(at) - 1), ...)
{
  stopifnot(require("gridBase"))
  z <- matrix(z[subscripts],
              nrow = length(unique(x[subscripts])),
              ncol = length(unique(y[subscripts])))
  if (!is.double(z)) storage.mode(z) <- "double"
  opar <- par(no.readonly = TRUE)
  on.exit(par(opar))
  if (panel.number() > 1) par(new = TRUE)
  par(fig = gridFIG(), omi = c(0, 0, 0, 0), mai = c(0, 0, 0, 0))
  cpl <- current.panel.limits()
  plot.window(xlim = cpl$xlim, ylim = cpl$ylim,
              log = "", xaxs = "i", yaxs = "i")
  # paint the color contour regions
  .Internal(filledcontour(as.double(do.breaks(cpl$xlim, nrow(z) - 1)),
                          as.double(do.breaks(cpl$ylim, ncol(z) - 1)),
                          z, as.double(at), col = col))

  # add the contour lines--this prints too many of them.  I really want
just
  # the lines dividing the color regions.
  contour(as.double(do.breaks(cpl$xlim, nrow(z) - 1)),
                            as.double(do.breaks(cpl$ylim, ncol(z) - 1)),
                            z, as.double(at), add=T,
          col = "gray", # color of the lines
          drawlabels=F  # add labels or not
         )
}

pdf("volcano.pdf")
plot.new()

print(levelplot(volcano, panel = panel.filledcontour,
          col.regions = terrain.colors,
          cuts = 10,
          plot.args = list(newpage = FALSE)))
dev.off()