plotting and coloring data on irregular grid

Question

I have data in the form (x, y, z) where x and y are not on a regular grid. I wish to display a 2D colormap of these data, with intensity (say, grey scale) mapped to the z va

Answer 1

Here is a lattice solution using deldir

d <- data.frame(x=runif(1e3, 0, 30), y=runif(1e3, 0, 30))
d$z = (d$x - 15)^2 + (d$y - 15)^2

pal1 <- grey(seq(0,1,leng=500))
library(latticeExtra)

 levelplot(z~x*y, data=d,
           panel = function(...) panel.voronoi(..., points=FALSE),
           interpolate=TRUE,
           col.regions = colorRampPalette(pal1)(1e3), cut=1e3)

Answer 2

Here's a solution based on dirichlet from the maptools package,

d <- data.frame(x=runif(1e3, 0, 30), y=runif(1e3, 0, 30))
d$z = (d$x - 15)^2 + (d$y - 15)^2

library(spatstat) 
library(maptools)

W <- ripras(df, shape="rectangle") 
W <- owin(c(0, 30), c(0, 30)) 
X <- as.ppp(d, W=W) 
Y <- dirichlet(X) 
Z <- as(Y, "SpatialPolygons") 
plot(Z, col=grey(d$z/max(d$z)))

I'm still unsure of the way to extract the polygons from this SpatialPolygons class.

Also if there's an easy way to produce the "correct" colors for the associated delaunay tesselation I'd like to hear it.