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I'm trying to open a .nc file with terra, but I'm getting the following error:

'' not recognised as a supported file format. (GDAL error 4)

Reproducible example here (16mb nc file):

if (!file.exists("HadISST_ice.nc")) { 
     download.file("https://www.metoffice.gov.uk/hadobs/hadisst/data/HadISST_ice.nc.gz","HadISST_ice.nc.gz")
     R.utils:::gunzip("HadISST_ice.nc.gz")
}
library(terra)
hadISST <- rast('HadISST_ice.nc')

The file opens with raster::brick, but not with terra:rast, which if I understand correctly from @robert-hijmnan answer is because raster uses ncdf4 while terra uses GDAL.

In GDAL the .nc file opens with no issues via terminal:

 % gdalinfo HadISST_ice.nc

Driver: netCDF/Network Common Data Format
Files: HadISST_ice.nc
Size is 512, 512

But I can't read the file with terra without throwing a GDAL error 4. Session info below:

print(sessionInfo())
R version 4.2.0 (2022-04-22)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Monterey 12.4
attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] terra_1.5-34

loaded via a namespace (and not attached):
[1] compiler_4.2.0   tools_4.2.0      Rcpp_1.0.8.3     codetools_0.2-18

and GDAL:

% gdal-config --version
GDAL 3.5.0, released 2022/05/10
marine-ecologist
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2 Answers2

3

edit: the problem seems to be related to be a MacOS specific issue with terra not being installed with netCDF drivers:

R terra gdal version incorrect, cannot read .nc (GDAL error 4)

installing the development version of terra solves the problem:

install.packages('terra', repos='https://rspatial.r-universe.dev’)

marine-ecologist
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    Thanks for posting a solution to your own question. I can confirm that this worked for me as of March, 2023. I am now running terra V1.7-19 on MacOS Ventura 13.0.1 and everything works just fine. – Juan Carlos Villaseñor Derbez Mar 08 '23 at 16:50
1

Another possible cause of the error 4 with terra package which I have just experienced:

If you have downloaded multiple .nc files from the web through R in Windows make sure to use mode = "wb" in the function argument

download.file(url = "https://example/xx.nc", destfile = "/example.nc", mode = "wb")
Eduardo Zanette
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