[R-sig-Geo] Transparency of Raster* objects

[Robert Hijmans]

Pierre,

There are two ways. You can use the alpha argument in plot, or in a function
that generates a vector of colors, see below. But note that this works in
the previous and in the next version of raster, but in the current version
only with 'oldstyle=TRUE'.  

>From ?slopeAspect

library(raster)
dem <- getData('alt', country='CHE')
slas <- slopeAspect(dem)
hill <- hillShade(slas[[1]], slas[[2]], 40, 270)

plot(hill, col=grey(0:100/100), legend=FALSE, main='Switzerland')
plot(dem, col=rainbow(25, alpha=0.35), add=TRUE)

plot(hill, col=grey(0:100/100), legend=FALSE, main='Switzerland')
plot(dem, col=rainbow(25), alpha=0.35, add=TRUE)

# for the current version, use oldstyle=T
plot(hill, col=grey(0:100/100), legend=FALSE, main='Switzerland')
plot(dem, col=rainbow(25, alpha=0.35), add=TRUE, oldstyle=T)

Robert

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