Transform rotated pole long/lat regular grid to unrotated curvilinear grid

Transform rotated long/lat regular grid to unrotated curvilinear grid

Usage

# S3 method for class 'stars'
st_rotate(.x, lon0, lat0, north = TRUE, ...)

# S3 method for class 'sfc'
st_rotate(.x, lon0, lat0, north = TRUE, ...)

# S3 method for class 'sf'
st_rotate(.x, lon0, lat0, north = TRUE, ...)

Arguments

.x: object of class stars
lon0: longitude of the rotated pole in degrees
lat0: latitude of the rotated pole in degrees
north: logical; if TRUE the pole refers to the North pole, otherwise the South pole
...: ignored

Value

curvilinear stars object with coordinates in regular long/lat (North pole at lat=90)

Examples

if (require("starsdata") && require("maps")) {
  # data downloaded from https://esgf-data.dkrz.de/search/cosmo-rea/
  nc = "netcdf/ts_EUR-6km_ECMWF-ERAINT_REA6_r1i1p1f1_COSMO_v1_mon_201801-201812.nc"
  f = system.file(nc, package = "starsdata")
  m = read_mdim(f, "ts")
  print(m)
  # NOTE this function is obsolete when reading m as
  # m = read_mdim(f, "ts", curvilinear = c("longitude", "latitude"))
  if (require(RNetCDF)) {
     x = open.nc(f)
     lon = att.get.nc(x, "rotated_latitude_longitude", "grid_north_pole_longitude")
     lat = att.get.nc(x, "rotated_latitude_longitude", "grid_north_pole_latitude")
     close.nc(x)
     print(c(lon = lon, lat = lat))
  } else {
     lon = -162
     lat = 39.25
  } 
  m1 = st_rotate(m, lon, lat)
  print(m1)
  h = function() maps::map(add = TRUE)
  plot(m1, downsample = c(10, 10, 5), axes = TRUE, hook = h, mfrow = c(1, 2)) 
    # curvilinear grid: downsample for plotting speed
  m2 = st_warp(m1, crs = st_crs("OGC:CRS84"), threshold = .1)
  plot(m2, hook = h, mfrow = c(3, 4)) # regular grid: plots fast
}
#> Loading required package: maps
#> stars object with 3 dimensions and 1 attribute
#> attribute(s), summary of first 1e+05 cells:
#>            Min.  1st Qu.   Median     Mean 3rd Qu.     Max.
#> ts [K] 277.3233 284.7061 286.1046 286.5914 288.003 296.9786
#> dimension(s):
#>      from  to offset delta refsys                    values x/y
#> rlon    1 848 -28.43 0.055     NA                      NULL [x]
#> rlat    1 824 -23.43 0.055     NA                      NULL [y]
#> time    1  12     NA    NA   Date 2018-01-16,...,2018-12-16    
#> Loading required package: RNetCDF
#>     lon     lat 
#> -162.00   39.25 
#> stars object with 3 dimensions and 1 attribute
#> attribute(s), summary of first 1e+05 cells:
#>            Min.  1st Qu.   Median     Mean 3rd Qu.     Max.
#> ts [K] 277.3233 284.7061 286.1046 286.5914 288.003 296.9786
#> dimension(s):
#>      from  to refsys                     values x/y
#> rlon    1 848 WGS 84 [848x824] -44.67,...,65.06 [x]
#> rlat    1 824 WGS 84  [848x824] 21.95,...,72.61 [y]
#> time    1  12   Date  2018-01-16,...,2018-12-16    
#> curvilinear grid

#> Warning: using Euclidean distance measures on geodetic coordinates
#> downsample set to 4