Building a task with a spatRaster backend...

[h-a-graham]

Hey,

So I've previously been using {mlr3spatiotempcv} and simply building the backend myself before creating a task using for example TaskRegrST$new().
But I really like the ideas presented in {mlr3spatial} of building the the task directly from the
SpatRaster object itself - especially for the prediction benefits - this look awesome.

But I'm struggling to actually build the task - here is a reprex:

suppressMessages({
  library(terra)
  library(mlr3)
  library(mlr3spatial)
})

f <- rast(system.file("ex/elev.tif", package="terra"))

rand <- rnorm(ncell(f), mean = 20, sd = 3)

f$newvar <- f$elevation[]*rand
f <- f*1 # to unite bands in memory (otherwise there is an error below)
plot(f)

be <- DataBackendRaster$new(f)

print(be)
#> <DataBackendRaster> (8550x2)
#>  elevation newvar
#>         NA     NA
#>         NA     NA
#>         NA     NA
#>         NA     NA
#>         NA     NA
#>         NA     NA
#> [...] (8544 rows omitted)
print(be$coordinates())
#>              x        y
#>    1: 6.004167 50.17917
#>    2: 6.012500 50.17917
#>    3: 6.020833 50.17917
#>    4: 6.029167 50.17917
#>    5: 5.970833 50.17083
#>   ---                  
#> 4604: 6.095833 49.46250
#> 4605: 5.979167 49.45417
#> 4606: 5.987500 49.45417
#> 4607: 6.029167 49.45417
#> 4608: 6.037500 49.45417
task = mlr3spatial::TaskRegrST$new(
  id = "elev",
  backend = be, #point_df
  target = "newvar",
  coordinate_names = c("x", "y"),
  coords_as_features = FALSE,
  crs = crs(f))
#> Error in .f(.xi, ...): Assertion on 'x' failed: Must be of type 'numeric', not 'NULL'.

^{Created on 2023-01-16 by the reprex package (v2.0.1)}

As you can see, the backend is created as expected and the coordinates are retained in the coordinates slot. But the coordinate_names argument is required for TaskRegrST but the columns are not present in the backend data table?

Any help would be greatly appreciated - many thanks!