The trick is I'm using RColorBrewer, who does not provides this
posibility.
No, but the alpha argument to plot (with a Raster* object) does:
r <- raster(system.file("external/test.grd", package="raster"))
library(RColorBrewer)
col <- brewer.pal(9, 'GnBu')
plot(r, col=col, alpha=0.3)
However, what I'm still stuck at using a variable transparency in
space, eg in the meuse.grid dataset, how to make transparency a
function of the distance to the river (the dist attribute) ?
I do not know; the below is ugly, but perhaps it provides some ideas:
library(raster)
data(meuse.grid)
coordinates(meuse.grid) <- ~x+y
proj4string(meuse.grid) <- CRS("+init=epsg:28992")
gridded(meuse.grid) <- TRUE
data(meuse.riv)
meuse.sr =
SpatialPolygons(list(Polygons(list(Polygon(meuse.riv)),"meuse.riv")))
r <- raster(meuse.grid, 'dist')
riv <- rasterize(meuse.sr, r)
d <- distance(riv)
d[d > 1000] <- 1000
d <- 254 * d/1000
a <- c(0:9, LETTERS[1:6])
bw <- paste("#000000", rep(a, each=16), rep(a, times=16), sep='')
plot(r)
plot(d, col=bw, add=T)
x11()
ter <- paste(substr(terrain.colors(254), 1, 7), rep(a, each=16),
rep(a, times=16), sep='')
plot(r, col=gray(1:255/255))
plot(d, col=ter, add=T)
Best, Robert
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