rggplot2kriginggeography

Transformation and export from R of a ggplot map to raster file (tiff)

In R, and RStudio, I have run his code:

#ordinary kriging

mydata.krig <- krige(Clay~1, train_data, newdata=mask, vgm)

names(mydata.krig)
names(mydata.krig)[1] <- "Clay.pred"
names(mydata.krig)

min(mydata.krig$Clay.pred, na.rm=T); max(mydata.krig$Clay.pred, na.rm=T) 

ggplot() +
geom_stars(data = mydata.krig["Clay.pred"]) +
scale_fill_gradient(low = "yellow", high = "dark blue", limits = c(15.5486,61.41131)) +
geom_sf(data = thessaly_smus, color = "black", fill = NA, size = 1) +
labs(title = "%Clay Predicted Values - Ordinary Kriging, OK")

With ggplot, I have also acquired a map of the predicted values of %Clay. I want to extract this map as a raster file from R in order to open it in a GIS, but only the area of interest (coloured polygons). Can you provide me accurate code for this?

enter image description here

Updated* With the help of @I_O, I wrote the code as you can see in comments, but again this is not my outcome that I want to take.I took the following outcome: enter image description here

But I want to create a raster file like this that will contain the clay predictions: enter image description here

Solution 
  • mydata.krig
#> stars object with 2 dimensions and 2 attributes
#> attribute(s):
#>                Min.  1st Qu.   Median      Mean   3rd Qu.     Max.  NA's
#> Clay.pred  15.80128 30.74017 36.38344  36.62676  43.28872  61.4972 63587
#> var1.var   85.52382 92.99561 96.14868 101.20852 100.43495 193.6164 63587
#> dimension(s):
#>   from  to  offset    delta              refsys x/y
#> x    1 346  267586  487.021 GGRS87 / Greek Grid [x]
#> y    1 248 4442456 -487.271 GGRS87 / Greek Grid [y]

    as mydata.krieg is a stars object, it’s quite easy to convert it to raster

    raster_ext <- sf::st_bbox(mydata.krig)
r <- raster::raster(t(mydata.krig[[1]]), 
       xmn = raster_ext[1], xmx = raster_ext[3],
       ymn = raster_ext[2], ymx=raster_ext[4],
       crs = sf::st_crs(mydata.krig)$proj4string)

terra::plot(r, col = grDevices::gray.colors(40))

    and write it to file

    raster::writeRaster(r, filename = "clay.tiff", overwrite = TRUE)