How to add text to a specific/fixed location in rasterVis levelplot

Question

In fact, this question is consist of two questions targeting the same behaviour.

1. How can I add text (varies by each panel) to a fixed location in panel area? I'm aware of panel.text and latticeExtra::layer solution but it adds text using plotting area coordinates. For instance, I want to add text to bottom-right corner of each panel even if their scales are different.

2. How to add text out of levelplot panel area(s)? Method explained here requires that levelplot has a plot_01.legend.top.vp area to add text which I don't have and the trellis object was plotted before. Besides, I want to add text to left of ylab shown in the figure below. I used ylab here to state the meaning of rows but I need a second ylab that represents y-axis values. I found another question for this problem but It does not work.

The plot above is created by raster::stack object and a rasterVis::levelplot method. I consent to a dirty solution even if I prefer an elegant one. Also despite the question above, I'm open to other approaches that use levelplot.

Upanishad

Not sure if it would help but names.attr in levelplot allows you to assign names to each panel. eg. names=c("One","Two","Three") and levelplot(yourstack, names.attr=names) – Fifteenth

Answer 1

A very similar issue is currently being discussed on R-sig-Geo, just have a look at the solution I provided there. Here is the corresponding sample code which lets you add custom text annotations inside or outside the panel regions of a trellis graph using trellis.focus(..., clip.off = TRUE) from lattice.

library(rasterVis)
library(grid)

## sample data
f <- system.file("external/test.grd", package="raster")
r <- raster(f)
s <- stack(r, r+500, r-500, r+200)

p <- levelplot(s, layout = c(2, 2), names.att = rep("", 4), 
               scales = list(y = list(rot = 90)))

## labels
cls <- c("col1", "col2")
rws <- c("row1", "row2")

png("~/rasterVis.png", width = 14, height = 16, units = "cm", res = 300L)
grid.newpage()
print(p, newpage = FALSE)

## loop over panels to be labelled (ie 1:3)
panels  = trellis.currentLayout()
for (i in 1:3) {

  # focus on current panel of interest and disable clipping
  ids <- which(panels == i, arr.ind = TRUE)
  trellis.focus("panel", ids[2], ids[1], clip.off = TRUE)

  # add labels
  if (i %in% c(1, 3)) {
    if (i == 1) {
      grid.text(cls[1], x = .5, y = 1.1)            # add 'col1'
      grid.text(rws[1], x = -.35, y = .5, rot = 90) # add 'row1'
    } else {
      grid.text(rws[2], x = -.35, y = .5, rot = 90) # add 'row2'
    }
  } else {
    grid.text(cls[2], x = .5, y = 1.1)              # add 'col2'
  }

  trellis.unfocus()
}

dev.off()

You may find some further information here:

• https://stat.ethz.ch/pipermail/r-help/2005-June/072745.html
• http://r.789695.n4.nabble.com/How-to-put-text-outside-an-xyplot-td975850.html

Alaniz