ScatterPlot between two rasters, giving color from a third raster

Question

I'm plotting two rasters data, producing the image below.

I'd like to color each point in the graph with a variable taken from a third raster data (with the same bbox, pixel size etc.). Any ideas from R-Users? This operation is very easy in plotting data from a dataset, but I don’t know about raster…

Here I attach the code (simplified, I think you don't need all the plot parameters e.g. abline, xlab and so on) that produced the image:

plot(mask(raster1, my_mask,maskvalue=0), #first raster, masked by my_mask
      mask(raster2, my_mask,maskvalue=0),  #second raster, masked by my_mask           
      col = alpha('black', 0.1), #the current color scheme     
      )
 raster3 #raster with categorical variable, 
         #that should give the colors to the points in the graph

Thanks a lot!

Answer 1

With the xyplot method defined in rasterVis you can use layers of a RasterStack as if they were columns of a data.frame. Therefore, they can be the components of the formula or the groups argument.

For example,

library(raster)
library(rasterVis)

f <- system.file("external/test.grd", package="raster")
r <- raster(f)
r2 <- r + 500 * init(r, rnorm)
## categorical variable
r3 <- cut(r, 3)

s <- stack(r, r2, r3)
names(s) <- c('r', 'r2', 'r3')

xyplot(r ~ r2, groups = r3, data = s,
       auto.key = list(space = 'right'),
       alpha = 1)