[R-sig-Geo] Strange spatial reference system netCDF

[Edzer Pebesma]

Dear Maurizio,

an attempt to do something along this line is:

f = "tas_rcp85_land-rcm_eur_12km_01_mon_198012-208011.nc"
library(stars)
r = read_ncdf(f, ncsub = cbind(start = c(1, 1, 1, 1), count = c(418,
406, 3, 1)), eps=1e-3)
rx = read_stars(f, proxy = TRUE) # only for the crs!
st_crs(r) = st_crs(rx)
r0 = stars:::st_transform_proj.stars(r, 4326)
png("x.png")
plot(r0[,,,1], border = NA, axes = TRUE, reset = FALSE)
library(rnaturalearth)
plot(ne_coastline(returnclass = "sf"), add = TRUE, col = 'orange')

Note that the output object time stamps respect the 360-day calendar
(using pkg PCICt).

You'll find some discussion, and the output image, here:
https://github.com/r-spatial/stars/issues/175

Feel free to post follow-up questions here, or to github.

On 5/2/19 6:49 PM, Maurizio Marchi wrote:
> Dear list,
> I'm working with large netCDF files from the UK Climate Projections portal (
> https://www.metoffice.gov.uk/research/collaboration/ukcp). More in detail
> I'm reading with the ncdf4 library this
> <http://data.ceda.ac.uk/badc/ukcp18/data/land-rcm/eur/12km/rcp85/01/tas/mon/latest/>
> file. Once loaded O can easily handle it but it is a strange reference
> system as follow:
> rotated_latitude_longitude[]
>             grid_mapping_name: rotated_latitude_longitude
>             longitude_of_prime_meridian: 0
>             earth_radius: *6371229*
>             grid_north_pole_latitude: 39.25
>             grid_north_pole_longitude: 198
>             north_pole_grid_longitude: 0
> If I load the .nc file in QGIS I see that the SR is "+proj=longlat
> +a=6371229 +b=6371229 +no_defs" where the values associated to *a* and
> *b* variables
> are the earth radius. Even if QGIS can read it, the raw file isn't
> projected properly (it seems tha QGIS is not able to handle such
> projection).
> Finally, using the ncdf4+raster libraries, I can easily generate e raster
> image but then I'm not able to understand I could I re project this raster
> in WGS84 reference system.
> Any helps?
> Cheers
> 
> --
> Maurizio Marchi,
> PhD Forest Science - Ecological Mathematics
> Skype ID: maurizioxyz
> linux user 552742
> #EUFGIS national Focal point for Italy
> #Annals of Silvicultural Research Associated Editor
> https://scholar.google.it/citations?hl=en&user=_2X6fu8AAAAJ
> <https://scholar.google.it/citations?hl=en&user=_2X6fu8AAAAJ*>
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics
Heisenbergstrasse 2, 48151 Muenster, Germany
Phone: +49 251 8333081

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