[GIS] Adjust text font size in plotting autofitvariogram in R

Question

It should be quite simple to adjust the font size in plotting the outcome ofautofitVariogram using the automap package. The text fonts for the number of pairs are too big; the text fonts for the model, nugget… information are too small and not presentable. I was able to adjust the size of the points, but I failed to adjust the font of the label (or remove them) and the model information.

I've tried:

library(automap)
data(meuse)
coordinates(meuse) <- c("x","y") 
data.auto.variogram <- autofitVariogram(formula = zinc ~1, input_data = meuse)
plot(data.auto.variogram, cex=1, par.settings=list(fontsize=list(text=5),par.main.text=list(cex=3), par.xlab.text=list(cex=2),par.ylab.text=list(cex=2)))

But that also reduces the size of the axis label and the information text.

We can use meuse as a reproducible example.

Can anyone give some solutions or recommendations please?

Answer 1

The text size of bottom-right annotations is hard-coded in autokrige.vgm.panel.r, which runs under the hood of automap's plot() method. The latter function is also responsible for creating point labels that are passed to gstat::vgm.panel.xyplot(), which is hard-coded as well. Now, you might get rid of these point labels through something like

## sample data
library(automap)
data(meuse)
coordinates(meuse) <- ~ x + y
afv <- autofitVariogram(formula = zinc ~ 1, input_data = meuse)
p <- plot(afv, plotit = FALSE)

## discard point labels
library(lattice)
opts <- trellis.par.get()
opts$add.text$col <- "transparent"
update(p, par.settings = opts)

or, similarly, opts$add.text$cex to reduce text size. However, this won't affect the bottom-right text section. In order to overcome this limitation, why not just define your own plotting function for objects of class 'autofitVariogram'? Taking inspiration from the source code of autokrige.vgm.panel.r, this requires little coding efforts and, at the same time, lets you modify the visual appearance of the resulting scatter plot at will.

## create custom text annotation
dgt <- function(x) if (x >= 10) 0 else if (x >= 1) 1 else 2

mdl <- afv$var_model
cls <- as.character(mdl[2, "model"])
ngt <- sum(mdl[1, "psill"])
sll <- sum(mdl[, "psill"])
rng <- sum(mdl[, "range"])
lbl <- paste("Model:", cls,
             "\nNugget:", round(ngt, dgt(ngt)),
             "\nSill:", round(sll, dgt(sll)),
             "\nRange:", round(rng, dgt(rng)))

if (cls %in% c("Mat", "Ste")) {
  kpp <- mdl[2, "kappa"]
  lbl <- paste(lbl, "\nKappa:", round(kpp, dgt(kpp)), "")
}

## create plot
xyplot(gamma ~ dist, data = afv$exp_var,
       main = "Experimental variogram and fitted variogram model", 
       xlab = "Distance", ylab = "Semi-variance",
       panel = function(x, y, ...) {
         gstat::vgm.panel.xyplot(x, y, cex = 1.2, ...)
         ltext(max(x), 0.2 * max(y), lbl, font = 2, cex = .9, adj = c(1, 0), 
               col = "grey30")
       }, 
       # arguments required by gstat::vgm.panel.xyplot()
       labels = NULL, mode = "direct", model = mdl, 
       direction = c(afv$exp_var$dir.hor[1], afv$exp_var$dir.ver[1]))