How to save after overlaying a spatial point data frame onto raster

Question

I tried to overlay a SpatialPointsDataFrame (yellow birds) onto a raster data (map). This was successful with the following R codes:

map1 = plot(map)

overlay_map = plot(yellowbirds,add=TRUE,col="blue")

However, when I want to regenerate the map by typing overlay_map , the output produced is Null instead of giving me the map.

How do I save the above correctly as a variable, so that I can generate the map without typing out the code again?

Answer 1

It is difficult to help you without any reproducible example.

However, if you only want to save the plot, you could do something like:

map1 <- plot(map)

overlay_map <- recordPlot()  #To save the next plot into an object

plot(yellowbirds,add=TRUE,col="blue")

Then, simply call the object again:

overlay_map

Answer 2

recordPlot is the right way to go, only that it saves the current plot (see ?recordPlot ) into a variable. I created this reproducible example :

library(raster)
map <- raster(system.file("external/test.grd", package="raster"))
yellowbirds <- SpatialPoints(
  coords = structure(c(179025.023681718, 179606.015156299, 179878.354910009, 
                       180441.19040101, 180913.245974108, 330055.067887591, 330508.967477108, 
                       331398.610672561, 331743.574360594, 332342.721818756), 
                     .Dim = c(5L, 2L), .Dimnames = list(NULL, c("x", "y"))))

plot(map)
map1 <- recordPlot()
plot(yellowbirds, add = TRUE)
overlay_map <- recordPlot()

Now we kill the current devices and reproduce the two plots:

dev.off()
map1
dev.off()
overlay_map

Both the map as well as the overlay_map should be recreated in the empty device. Even if you rm(map1) , overlay_map will plot correctly.

NOTE: Do not call plot(overlay_map) as it produces the following error

Error in xy.coords(x, y, xlabel, ylabel, log) : 'x' is a list, but does not have components 'x' and 'y'