如何为rasterStack中的所有栅格图层显示相同的图例

Question

I've looked through all SO but haven't been able to find an answer to this specific question:

I have a rasterStack with several layers whose values span over a quite large range. Knowing the values of each layer and the chosen colour scale I believe I have managed to plot all the rasters with the same colour scale, but I face three problems now:

1. I can't be sure that the values are being plotted with the same colour scale, although it seems like it
2. I can't manage to plot the same scale and scale labels for all layers.
3. One of my cells in ras3, ras3[3,9] , doesn't get coloured, but it is not NA!

Example script follows:

library(raster)
# generate example rasters
set.seed(123)
ras1 <- raster(ncol = 10, nrow= 10)
values(ras1) <- runif(100, 1, 10)

ras2 <- raster(ncol = 10, nrow = 10)
values(ras2) <- runif(100, 5, 50)

ras3 <- raster(ncol = 10, nrow = 10)
values(ras3) <- runif(100, 10, 100)

# stack them 
rasStack <- stack(ras1, ras2, ras3)
# plot normally to check the values
plot(rasStack)

# obtain max and min values 
maxv <- max(maxValue(rasStack))+1
minv <- min(minValue(rasStack))

# set the breaks between min and max values
brks <- seq(minv,maxv,by=0.1)
nbrks <- length(brks)-1
r.range <- c(minv, maxv)

# generate palette
colfunc<-colorRampPalette(c("springgreen", "royalblue", "yellow", "red"))

# plot in a loop with a common legend, using legend.only = T    
for(i in seq_len(nlayers(rasStack))){
  tmp <- rasStack[[i]]
  plot(tmp, breaks=brks,col=colfunc(nbrks), legend = F, zlim=c(minv,maxv), 
  main = names(tmp))
  plot(tmp, legend.only=TRUE, col=colfunc(nbrks),
       legend.width=1, legend.shrink=0.75,
       axis.args=list(at=seq(minv, maxv, 5),
                  labels=round(seq(r.range[1], r.range[2], 5), 2), 
                  cex.axis=0.6),
   legend.args=list(text='value', side=4, font=2, line=2.5, cex=0.8))}

# check that the blank cell has a valid value
ras3[3, 9]
> 99.01704 

Any help will be greatly appreciated!

---

EDIT: as per ycw's answer I've edited the code and now problem no. 3 has disappeared!

Answer 1

I just fixed this problem so I'll post the solution in case someone else stumbles with this.

I might be a bit of a workaround, and it certainly is not very elegant, but it works:

First of all we add up all three raster layers in a new one

rasTot <- ras1 + ras2 + ras3

Now we run the loop from the previous code but in the plot with the legend.only call we use this total raster.

for(i in seq_len(nlayers(rasStack))){
  tmp <- rasStack[[i]]
  plot(tmp, breaks=brks,col=colfunc(nbrks), legend = F, zlim=c(minv,maxv), 
  main = names(tmp))
  plot(rasTot, legend.only=TRUE, col=colfunc(nbrks),
       legend.width=1, legend.shrink=0.75,
       legend.args=list(text='value', side=4, font=2, line=2.5, cex=0.8))
}

I also edited out some of the legend label specifications, as the defaults are OK.

Answer 2

The last break number should be larger than the maximum value of your data ( maxv ) so that the cell with the maximum can be colored based on the last color category. Otherwise, the cell will be blank.

I modified your code by changing maxv <- max(maxValue(rasStack)) + 1 but did not change other parts. The result looks good.