Unit metadata from aux.json not used when reading SpatRaster

[brownag]

For reading file types where SpatRaster metadata are stored in an aux.json file, it appears units are not always set in the result.

With most recent CRAN (1.8.5) and current development (1.8.7), reading GeoTIFF metadata works fine, but with other file types, e.g. netCDF and GRD, units(x) returns "" rather than the expected value "m". It appears the correct values are written to aux.json file, and that reading fails to load the units into the new SpatRaster object

library(terra)
#> terra 1.8.7

dir.create("metadata_test", showWarnings = FALSE)

x <- rast(system.file("ex", "elev.tif", package = "terra"))
x
#> class       : SpatRaster 
#> dimensions  : 90, 95, 1  (nrow, ncol, nlyr)
#> resolution  : 0.008333333, 0.008333333  (x, y)
#> extent      : 5.741667, 6.533333, 49.44167, 50.19167  (xmin, xmax, ymin, ymax)
#> coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#> source      : elev.tif 
#> name        : elevation 
#> min value   :       141 
#> max value   :       547

time(x) <- as.Date("2024-12-25") 
units(x) <- "m"
x
#> class       : SpatRaster 
#> dimensions  : 90, 95, 1  (nrow, ncol, nlyr)
#> resolution  : 0.008333333, 0.008333333  (x, y)
#> extent      : 5.741667, 6.533333, 49.44167, 50.19167  (xmin, xmax, ymin, ymax)
#> coord. ref. : lon/lat WGS 84 (EPSG:4326) 
#> source      : elev.tif 
#> name        : elevation 
#> min value   :       141 
#> max value   :       547 
#> unit        :         m 
#> time (days) : 2024-12-25

writeRaster(x, "metadata_test/test.tif", overwrite = TRUE)

# works stored internally in TIFF
y <- rast("metadata_test/test.tif")
time(y)
#> [1] "2024-12-25"
units(y)
#> [1] "m"


# does not work, units in aux.json but not result
writeRaster(x, "metadata_test/test2.nc", overwrite=T)
#> Warning: [writeRaster] consider writeCDF to write ncdf files
y <- rast("metadata_test/test2.nc")
cat(readLines("metadata_test/test2.nc.aux.json"), sep = "\n")
#> {
#> "time":["2024-12-25"],
#> "timestep":"days",
#> "unit":["m"]
#> }
time(y)
#> [1] "2024-12-25"
units(y)
#> [1] ""

# does not work, units in aux.json but not result
writeRaster(x, "metadata_test/test3.grd", overwrite=T)
y <- rast("metadata_test/test3.grd")
cat(readLines("metadata_test/test3.grd.aux.json"), sep = "\n")
#> {
#> "time":["2024-12-25"],
#> "timestep":"days",
#> "unit":["m"]
#> }
time(y)
#> [1] "2024-12-25"
units(y)
#> [1] ""

[rhijmans]

Thank you. I now get:

library(terra)
dir.create("metadata_test", showWarnings = FALSE)
x <- rast(system.file("ex", "elev.tif", package = "terra"))
time(x) <- as.Date("2024-12-25") 
units(x) <- "m"

y <- writeRaster(x, "metadata_test/test.tif", overwrite = TRUE)
time(y)
[#1] "2024-12-25"
units(y)
#[1] "m"
 
z <- writeRaster(x, "metadata_test/test2.nc", overwrite=T)
#Warning message:
#[writeRaster] consider writeCDF to write ncdf files 
time(z)
#[1] "2024-12-25"
units(z)
#[1] "m"
 
a <- writeRaster(x, "metadata_test/test3.grd", overwrite=T)
time(a)
#[1] "2024-12-25"
units(a)
#[1] "m"