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rplotlegendlatticelevelplot

Add sp.points key to levelplot colorkey

Is it possible to add the key for, e.g., an sp.points layer, to the colorkey generated by levelplot?

Take the following example:

library(rasterVis)
library(latticeExtra)
library(sp)

r <- as.factor(raster(matrix(rbinom(100, 1, 0.5), 10)))
levels(r)[[1]] <- data.frame(ID=0:1, z=c('a', 'b'))
p <- SpatialPoints(matrix(runif(20), 10))

levelplot(r, margin=list(draw=FALSE), scales=list(draw=FALSE),
          col.regions=c('white', 'gray90')) +
  latticeExtra::layer(sp.points(p, pch=20, col=1))

enter image description here

I would like to add a key entry for the points, below the existing colorkey.

A kludgy solution is to add a key to the levelplot call as follows, adjusting the x and y values until it's in the desired location, but (1) finding the right x and y values is a pain, requiring interaction, (2) the right padding doesn't resize to accommodate the key, and (3) the font size is not automatically scaled to be consistent with the colorkey.

k <- list(x = 1.02, y = 0.4, corner = c(0, 0), points=list(pch=20, col=1), 
          text=list('foo', cex=0.9))

levelplot(r, margin=list(draw=FALSE), scales=list(draw=FALSE),
          col.regions=c('white', 'gray90'), key=k) +
  latticeExtra::layer(sp.points(p, pch=20, col=1))

enter image description here

Assuming I need to stick with lattice graphics, what's the best way to overcome the issues I listed above?

Solution

  • Although it does not solve all the issues you raised, maybe the latticeExtra::mergedTrellisLegendGrob function is useful for you:

    p1 <- levelplot(r, scales=list(draw=FALSE),
                col.regions=c('white', 'gray90'))

myPoints <- SpatialPoints(matrix(runif(20), 10))
p2 <- spplot(myPoints, pch=20)

## Merge graphics
p <- p1 + p2

## Merge legends
l1 <- p1$legend$right
l2 <- p2$legend$bottom
ll <- mergedTrellisLegendGrob(l1, l2)
p$legend$right$fun <- ll

p

    mergedLegends