Building a raster with a color ramp diverging around zero

Question

I am trying to build a map with positive and negative values.

All positive values ​​should be red, while negative should be blue and zero should be white, as in this example, with discrete colors

The following is the code I'm using:

library (rasterVis)
ras1 <- raster(nrow=10,ncol=10) 
set.seed(1) 
ras1[] <- rchisq(df=10,n=10*10) 
ras2=ras1*(-1)/2 
s <- stack(ras1,ras2) 
levelplot(s,par.settings=RdBuTheme())

Thanks so much for providing a general solution that can be applied to other mapping exercises.

Answer 1

gist, . trellis, rasterVis::levelplot, , , .

s, :

devtools::source_gist('306e4b7e69c87b1826db')
p <- levelplot(s)
diverge0(p, ramp='RdBu')

ramp RColorBrewer, colorRampPalette.

---

:

diverge0 <- function(p, ramp) {
  # p: a trellis object resulting from rasterVis::levelplot
  # ramp: the name of an RColorBrewer palette (as character), a character 
  #       vector of colour names to interpolate, or a colorRampPalette.
  require(RColorBrewer)
  require(rasterVis)
  if(length(ramp)==1 && is.character(ramp) && ramp %in% 
     row.names(brewer.pal.info)) {
    ramp <- suppressWarnings(colorRampPalette(brewer.pal(11, ramp)))
  } else if(length(ramp) > 1 && is.character(ramp) && all(ramp %in% colors())) {
    ramp <- colorRampPalette(ramp)
  } else if(!is.function(ramp)) 
    stop('ramp should be either the name of a RColorBrewer palette, ', 
         'a vector of colours to be interpolated, or a colorRampPalette.')
  rng <- range(p$legend[[1]]$args$key$at)
  s <- seq(-max(abs(rng)), max(abs(rng)), len=1001)
  i <- findInterval(rng[which.min(abs(rng))], s)
  zlim <- switch(which.min(abs(rng)), `1`=i:(1000+1), `2`=1:(i+1))
  p$legend[[1]]$args$key$at <- s[zlim]
  p$par.settings$regions$col <- ramp(1000)[zlim[-length(zlim)]]
  p
}

, , @LucasFortini post, , , colorkey , : levelplot(s,par.settings=RdBuTheme(), at=seq(-max(abs(cellStats(s, range))), max(abs(cellStats(s, range))), len=100)).

Answer 2

, script :

library(colorRamps)
col5 <- colorRampPalette(c('blue', 'gray96', 'red'))  #create color ramp starting from blue to red
color_levels=20 #the number of colors to use
max_absolute_value=0.4 #what is the maximum absolute value of raster?
plot(img, col=col5(n=color_levels), breaks=seq(-max_absolute_value,max_absolute_value,length.out=color_levels+1) , axes=FALSE)

, script:

library(raster)
library(colorRamps)
mask_data=shapefile("D:/temp/so/Main_Hawaiian_Islands_simple3.shp")
img=raster("D:/temp/so/PPT_wet_minus_dry.tif")
col5 <- colorRampPalette(c('blue', 'gray96', 'red'))  #create color ramp starting from blue to red
color_levels=10 #the number of colors to use
max_absolute_value=max(abs(c(cellStats(img, min), cellStats(img, max)))) #what is the maximum absolute value of raster?
color_sequence=seq(-max_absolute_value,max_absolute_value,length.out=color_levels+1)
plot(img, col=col5(n=color_levels), breaks=color_sequence, axes=FALSE)
plot(mask_data, add=T)

, , ( , ). :

n_in_class=hist(img, breaks=color_sequence, plot=F)$counts>0
col_to_include=min(which(n_in_class==T)):max(which(n_in_class==T))
breaks_to_include=min(which(n_in_class==T)):(max(which(n_in_class==T))+1)
plot(img, col=col5(n=color_levels)[col_to_include], breaks=color_sequence[breaks_to_include] , axes=FALSE)
plot(mask_data, add=T)