How can I add a subplot within a plot using levelplot in R?

Question

I would like to add a subplot in my main levelplot, something similar to this image . I want lat/lon axis for both my maps but I have not managed to find a way to do this with the levelplot. Also, I've seen this question but has no answer. I am quite confused about the subplot and the new par(), so I would really like some help.

library("raster")
library ("rasterVis")
library("viridis")

r <- raster(system.file("external/test.grd", package="raster"))#subplot
r2<-r/2 #main plot
ckey <- list(labels=list(cex=1.5), height=1,space='top')
levelplot(r2,colorkey=ckey,margin=FALSE,xlab="", ylab="",col.regions=viridis,at=seq(100,500, len=20),
          scales=list(x=list(cex=1.5),y=list(cex=1.5))) #from this point, I do not know how to add a subplot

Answer 1

grid.arrange from the gridExtra package can do that for you

library(raster)
library(rasterVis)
library(viridis)
library(gridExtra)

r <- raster(system.file("external/test.grd", package = "raster")) # subplot
r2 <- r / 2 # main plot
ckey <- list(labels = list(cex = 1.5), height = 1, space = "top")

lv1 <- levelplot(r2,
  colorkey = ckey, margin = FALSE, xlab = "", ylab = "", col.regions = viridis, at = seq(100, 500, len = 20),
  scales = list(x = list(cex = 1.5), y = list(cex = 1.5))) # from this point, I do not know how to add a subplot

lv2 <- levelplot(r2,
  colorkey = ckey, margin = FALSE, xlab = "", ylab = "", col.regions = viridis, at = seq(100, 500, len = 20),
  scales = list(x = list(cex = 1.5), y = list(cex = 1.5)))

lay <- rbind(
  c(1, 1, NA, NA, NA),
  c(1, 1, 2, 2, 2),
  c(NA, NA, 2, 2, 2),
  c(NA, NA, 2, 2, 2)
)

grid.arrange(lv1, lv2, layout_matrix = lay,
             top = "Figure 1.", 
             bottom = "bottom\nlabel")

^{Created on 2019-11-22 by the reprex package (v0.3.0)}