support for adding a dictionary of layer-specific metadata tags?

[mikoontz-vp]

I'm following up on this StackOverflow answer (https://stackoverflow.com/questions/71367060/write-rasterstack-and-preserve-metadata-in-r) and the request to make a feature request here if this is functionality that we might find useful.

It's my understanding that python's rasterio can write arbitrary metadata to the layers of multiband raster as a dictionary when writing a GTIFF to disk. E.g., to include a "start_date" tag for each layer of a 6-band raster that each represents a new year, we might write:

# need input_raster_array and input_raster_profile
with rasterio.open(
    output_filename, "w", **(input_raster_profile)
) as dst:
    dst.write(input_raster_array)
    for index in range(0, 6):
        year = 2017 + index
        dst.update_tags(index + 1, **{'start_date': f"{year}-01-01"})

I know that we can now write band names on disk (which is great!) and I think the extra tagging functionality would also add to metadata management.

[mikoontz-vp]

I've figured out a workaround to use the {reticulate} interface to Python's {rasterio} package. The following will add a tag called start_date to the first band of the raster in the local file "my_file.tif":

# reticulate::py_install("rasterio")
rasterio = reticulate::import("rasterio")
src = rasterio$open("my_file.tif", mode = "r+")

src$update_tags(1, start_date="2019-01-01")

# Tags will be written when the file is closed for writing
src$close()

# Make sure it works
print(src$tags(1))

# Use {terra} to confirm it works
terra::meta("my_file.tif", layers = TRUE)

[rhijmans]

file level tags can now be set with metags<- but I need to expand that to layer level tags.

[mikoontz-vp]

Awesome, thanks @rhijmans!

[rhijmans]

I took me a while, but with e069502 it is now possible to add user defined layer specific tags and write/read them to/from GTiff. Note that "time" variables are handled automatically so that they are recognized and recovered as such.

library(terra)
#terra 1.8.2

r <- rast(ncol=5, nrow=5, nlyr=2, vals=1)
m <- cbind(c("one", "two", "three"), c("ABC", "123", "hello"))
metags(r) <- m
metags(r, layer=1) <- c(another_tag="44", `one more`="that value")
metags(r, layer=2) <- c(another_tag="55")

x <- writeRaster(r, "test.tif", overwrite=TRUE)
metags(x)
#    one   three     two 
#  "ABC" "hello"   "123" 
metags(x, 1:2)
#  layer        name      value
#1     1 another_tag         44
#2     1    one more that value
#3     2 another_tag         55
 
metags(x, 1, "one more")
#  layer     name      value
#2     1 one more that value

metags(x, 2, "one more")
#[1] layer name  value
#<0 rows> (or 0-length row.names)

Please let me know if this is not flexible enough for you (by opening a new issue).