Choosing CRS / PROJ4 string for EURO-Cordex rotated pole projection?

Question

I have to analyze some CORDEX models which have a rotated pole projection. The projection is described in this document, see page 10, Table 1, row "Europe high res".

I have tried to describe the proj4 string like so: +proj=ob_tran +o_proj=longlat +o_lon_p=-162.0 +o_lat_p=39.25 +lon_0=180 +lat_0=0, but it seems that this is not correct, at least using sf in R:

st_crs(rsf) <- "+proj=ob_tran +o_proj=longlat +o_lon_p=-162.0 +o_lat_p=39.25 +lon_0=180 +lat_0=0"
Warning message:
In CPL_crs_from_proj4string(x) :
  Cannot import crs from PROJ.4 string `+proj=ob_tran +o_proj=longlat +o_lon_p=-162.0 +o_lat_p=39.25 +lon_0=180 +lat_0=0', missing crs returned

What is the correct CRS for this projection?

Answer 1

With the help of Edzer and others we conjured a solution that works. See the GitHub issue here. It is a workaround and is not the most beautiful approach, but it works.

Basically using the proj.4 crs "+proj=ob_tran +o_proj=longlat +o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +to_meter=0.01745329" works, with the caveat of using R lwgeom to project instead of sf::st_transform, since GDAL currently does not understand this projection (it will in the next version).

# d is the input dataset saved in an sf object
x <- lwgeom::st_transform_proj(d, c(st_crs(4326)$proj4string, "+proj=ob_tran +o_proj=longlat +o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +to_meter=0.01745329"))
sf:st_crs(x) = NA # ?! This is mandatory for some reason
sf::st_crs(x) = 4326
sf::plot(x, axes = TRUE)

Answer 2

Another simpler approach is to use the "terra" package to open the nc or raster files and then assign the projection.

library(terra)

# Upload data where d is the input dataset in a nc or raster object
     x <- terra::rast("d")

# Define projection    
    crs<-"+proj=ob_tran +o_proj=longlat +o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +to_meter=0.01745329"

# Change projection    
    x <- project(x, crs)